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  • Journal article
    Mohammed A, Gaduan A, Chaitram P, Pooran A, Lee K-Y, Ward Ket al., 2023,

    Sargassum inspired, optimized calcium alginate bioplastic composites for food packaging

    , Food Hydrocolloids, Vol: 135, Pages: 1-12, ISSN: 0268-005X

    Plastic pollution, more specifically from food packaging and containers which account for the largest share of 36% of current plastic production, is one of the greatest threats to the natural environment and human health. Thus, the development of alternative renewable plastics are needed to complement a circular economy and reduce resource depletion. Seaweeds have been known to possess good film forming properties ideal for bioplastic production, and Sargassum natans-an invasive brown seaweed which has been inundating the shores of the Caribbean, has been shown to be an excellent candidate. This study presents, for the first time, the development of a novel optimized biodegradable alginate composite bioplastic as an alternative to traditional plastic packaging. The optimization process was carried out using Response Surface Methodology (RSM) resulting in a formulation of 6 wt% alginate, 0.263 wt% starch, 0.35 wt% CMC, 0.065 g/g sorbitol and 0.025 g/g PEG 200- with ultra-high oxygen barrier (OP - 0.2 cm3 μm m−2 d−1 kPa−1), good water vapor barrier (WVP - 2.18 × 10−12 g m/m2 s Pa) and high tensile modulus ( - 3.93 GPa)- with no migration of additives into a simulated aqueous food system in 10 days. Furthermore, composite films were found to fully degrade in 14 days and possessed better OP, higher WVP and comparable material properties to HDPE, PET and PLA. Ultimately, our results support alginate composite films as a viable alternative for food packaging best fitted for low moisture environments-encouraging the use of renewable materials for packaging innovation and supporting UNSDGs.

  • Journal article
    Gaduan AN, Li J, Hill G, Wallis C, Burgstaller C, Lee K-Yet al., 2023,

    Simulating the recycling of milk bottles in the UK: Influence of blending virgin and repeatedly melt-extruded high-density polyethylene

    , Resources, Conservation and Recycling, Vol: 189, Pages: 1-8, ISSN: 0921-3449

    The UK Dairy Roadmap has set a target of achieving 50 wt.-% high density polyethylene (HDPE) recyclate in their HDPE milk bottles. Such high recyclate content will lead to the accumulation of HDPE recyclates that have been subjected to different number of melt extrusion cycles in the supply chain. This work investigates the structure-property relationship of blending virgin HDPE (vHDPE) with these different grades of repeatedly melt-extruded HDPE (rHDPE). HDPE was subjected to 10, 20 and 50 melt-extrusion cycles and blended with vHDPE. No significant difference in terms of melt rheology, tensile properties and overall migration in acidic and aqueous environments of the blends of the different rHDPEs with vHDPE was observed when compared to vHDPE. This study demonstrates the feasibility of blending up to 50 wt.-% rHDPE of different grades with vHDPE as set out in the UK Dairy Roadmap.

  • Journal article
    Caro-Astorga J, Lee K, Ellis T, 2022,

    Increasing bacterial cellulose compression resilience with glycerol or PEG400 as a route to more robust engineered living materials

    , Carbohydrate Polymer Technologies and Applications, Vol: 4, Pages: 1-6, ISSN: 2666-8939

    Bacterial cellulose (BC) is one of the current natural materials at the edge of innovation in engineered living materials (ELMs) research due to its ease of growth and outstanding properties as a hydrogel. One of the main limitations of this material, however, is its quick dehydration in open environments as water molecules leave the porous network. Here we show that other solvents with higher evaporation temperatures, namely glycerol and polyethylene glycol (PEG), can play the same role as water within the BC structure interacting with cellulose fibres via hydrogen bonds. We demonstrate that these molecules provide up to a 130-fold improvement in the Young´s Modulus of BC hydrogels to compression forces in a concentration dependent manner. To take advantage of these effects for application in BC-based ELMs produced by Komagataeibacter rhaeticus, we also explored the effect of glycerol and PEG400 on the survival of the BC-producing bacteria in BC pieces. PEG400 at 20% doubled the material resilience to compression forces, still allowing bacteria to survive within the material for weeks. These results open further opportunities to explore new applications and stacked storage conditions.

  • Journal article
    Ketola AE, Song W, Lappalainen T, Salminen K, Viitala J, Turpeinen T, Miettinen A, Lee K-Y, Ketoja JAet al., 2022,

    Changing the structural and mechanical anisotropy of foam-formed cellulose materials by affecting bubble-fiber interaction with surfactant

    , ACS Applied Polymer Materials, Vol: 4, Pages: 7685-7698, ISSN: 2637-6105

    Cellulose fiber materials suitable for filtering, insulation, protective, and hygiene applications can be formed using aqueous foam as a carrier phase. The subtle fiber–bubble interaction provides a tool which can be utilized to alter both structural and mechanical material properties. Earlier model surface studies have only indicated clear surface-bubble adhesion when both the surface hydrophobicity and surface tension of the solution are high enough. In this work, we first show that for silica model surfaces these basic mechanisms are similar for both nonionic polyethylene glycol sorbitan monolaurate (Tween 20) and anionic sodium dodecyl sulfate (SDS) surfactants. In the second step, thick nonwoven materials were foam formed from hydrophilic or hydrophobic viscose fibers using small amounts of cellulose microfibers (CMFs) to form a bonding agent. There was a clear variation in structure and strength properties between the samples made using different fibers and surfactants. The partial alignment and layering of fibers in the wet foam led to anisotropy in the mechanical properties of the formed samples. Using SDS, the fiber alignment was very strong for hydrophilic fibers but was reduced for hydrophobic fibers because of stronger coupling to bubbles during structure forming, impacting the microscale fiber network. For nonionic Tween 20, in addition to surfactant adsorption on the fibers, the ethoxylated surfactant headgroups are suggested to form bridges between CMFs and other fibers, restricting fiber movements during formation. For hydrophilic fibers, this showed up as a lower in-plane compression modulus but higher transverse strength for Tween 20 compared with SDS surfactant. For hydrophobic fibers, the sensitivity of the mechanical properties on surfactant type was even stronger.

  • Journal article
    Titirici M, Baird SG, Sparks TD, Yang SM, Brandt-Talbot A, Hosseinaei O, Harper DP, Parker RM, Vignolini S, Berglund LA, Li Y, Gao H-L, Mao L-B, Yu S-H, Diez N, Ferrero GA, Sevilla M, Szilagyi PA, Stubbs CJ, Worch JC, Huang Y, Luscombe CK, Lee K-Y, Luo H, Platts MJ, Tiwari D, Kovalevskiy D, Fermin DJ, Au H, Alptekin H, Crespo-Ribadeneyra M, Ting VP, Fellinger T-P, Barrio J, Westhead O, Roy C, Stephens IEL, Nicolae SA, Sarma SC, Oates RP, Wang C-G, Li Z, Loh XJ, Myers RJ, Heeren N, Gregoire A, Perisse C, Zhao X, Vodovotz Y, Earley B, Finnveden G, Bjorklund A, Harper GDJ, Walton A, Anderson PAet al., 2022,

    The sustainable materials roadmap

    , Journal of Physics: Materials, Vol: 5, Pages: 1-98, ISSN: 2515-7639

    Over the past 150 years, our ability to produce and transform engineered materials has been responsible for our current high standards of living, especially in developed economies. However, we must carefully think of the effects our addiction to creating and using materials at this fast rate will have on the future generations. The way we currently make and use materials detrimentally affects the planet Earth, creating many severe environmental problems. It affects the next generations by putting in danger the future of the economy, energy, and climate. We are at the point where something must drastically change, and it must change now. We must create more sustainable materials alternatives using natural raw materials and inspiration from nature while making sure not to deplete important resources, i.e. in competition with the food chain supply. We must use less materials, eliminate the use of toxic materials and create a circular materials economy where reuse and recycle are priorities. We must develop sustainable methods for materials recycling and encourage design for disassembly. We must look across the whole materials life cycle from raw resources till end of life and apply thorough life cycle assessments (LCAs) based on reliable and relevant data to quantify sustainability. We need to seriously start thinking of where our future materials will come from and how could we track them, given that we are confronted with resource scarcity and geographical constrains. This is particularly important for the development of new and sustainable energy technologies, key to our transition to net zero. Currently 'critical materials' are central components of sustainable energy systems because they are the best performing. A few examples include the permanent magnets based on rare earth metals (Dy, Nd, Pr) used in wind turbines, Li and Co in Li-ion batteries, Pt and Ir in fuel cells and electrolysers, Si in solar cells just to mention a few. These materials are classified as

  • Journal article
    Herrera N, Li J, Lee K-Y, 2022,

    Tough poly(ethylene glycol)-sized bacterial cellulose sheet for high impact strength laminated acrylic composites

    , Composites Part A: Applied Science and Manufacturing, Vol: 156, Pages: 1-8, ISSN: 1359-835X

    Dried and well-consolidated sheet of bacterial cellulose (BC) nanofibrils is a material structure that possesses high modulus and strength but is also brittle, which limits its potential in various advanced composite applications. Here, we report a simple method of enhancing the toughness of BC sheet by sizing the BC nanofibrils with poly(ethylene glycol) (PEG). This hinders interfibril hornification and facilitates large-scale BC nanofibril debonding, slippage and reorientation upon deformation. The PEG-sized BC sheets show high tensile strain-at-failure and work of fracture compared to neat BC sheet. PEG-sized BC reinforced laminated acrylic composites achieve a flatwise Charpy impact strength of up to 26 kJ m−2. This is a remarkable increase over the impact strength of neat impact-modified acrylic of only 12 kJ m−2, especially when the BC loading required to achieve this radical improvement is only 0.2 wt-%. Our study opens new paradigm in using low BC loading to achieve performance improvements suitable for high value composite applications.

  • Journal article
    Gaduan A, Singkronart K, Bell C, Tierney E, Burgstaller C, Lee K-Yet al., 2022,

    Mechanical upcycling immiscible polyethylene terephthalate-polypropylene blends with carbon fibre reinforcement

    , ACS Applied Polymer Materials, Vol: 4, ISSN: 2637-6105

    Ineffective sorting of post-consumer plastics remains one of the major obstacles in the recycling of plastics. Consequently, these highly heterogeneous, mixed post-consumer plastics will end up in landfill or have to be incinerated as repurposing them directly would lead to a polymer blend with inferior quality for many end-uses. In this work, we demonstrate the use of carbon fibers (CFs) to practically upgrade the mechanical properties of mixed plastics, adding value to them. This will create a stronger demand for mixed plastics to be used in various engineering applications. Using polyethylene terephthalate (PET) and polypropylene (PP) as the model immiscible polymer blend, we showed that the incorporation of CFs increased the tensile, flexural, and single-edge notched fracture toughness of the resulting CF-reinforced PET/PP composite blends. Despite the high environmental burden associated with the production of CFs, cradle-to-grave life-cycle analysis showed that CF-reinforced PET/PP composites have a lower environmental impact than the life-cycle scenarios of “doing nothing” and repurposing immiscible PET/PP blends as it is without CF reinforcement. This can be attributed to the weight saving achieved, a direct result of their higher mechanical performance. Our work opens up opportunities for the use of mixed plastics in various higher value applications such that they can be diverted away from landfill or incineration, in line with the concept of circular economy.

  • Journal article
    Eichhorn SJ, Etale A, Wang J, Berglund LA, Li Y, Cai Y, Chen C, Cranston ED, Johns MA, Fang Z, Li G, Hu L, Khandelwal M, Lee K-Y, Oksman K, Pinitsoontorn S, Quero F, Sebastian A, Titirici MM, Xu Z, Vignolini S, Frka-Petesic Bet al., 2022,

    Current international research into cellulose as a functional nanomaterial for advanced applications

    , Journal of Materials Science, Vol: 57, Pages: 5697-5767, ISSN: 0022-2461

    This review paper provides a recent overview of current international research that is being conducted into the functional properties of cellulose as a nanomaterial. A particular emphasis is placed on fundamental and applied research that is being undertaken to generate applications, which are now becoming a real prospect given the developments in the field over the last 20 years. A short introduction covers the context of the work, and definitions of the different forms of cellulose nanomaterials (CNMs) that are most widely studied. We also address the terminology used for CNMs, suggesting a standard way to classify these materials. The reviews are separated out into theme areas, namely healthcare, water purification, biocomposites, and energy. Each section contains a short review of the field within the theme and summarizes recent work being undertaken by the groups represented. Topics that are covered include cellulose nanocrystals for directed growth of tissues, bacterial cellulose in healthcare, nanocellulose for drug delivery, nanocellulose for water purification, nanocellulose for thermoplastic composites, nanocellulose for structurally colored materials, transparent wood biocomposites, supercapacitors and batteries.

  • Journal article
    Goosens V, Walker K, aragon S, Singh A, Senthivel V, Dekker L, Caro Astorga J, Buat M, Song W, Lee KY, Ellis Tet al., 2021,

    Komagataeibacter tool kit (KTK): a modular cloning system for multigene constructs and programmed protein secretion from cellulose producing bacteria

    , ACS Synthetic Biology, Vol: 10, Pages: 3422-3434, ISSN: 2161-5063

    Bacteria proficient at producing cellulose are an attractive synthetic biology host for the emerging field of Engineered Living Materials (ELMs). Species from the Komagataeibacter genus produce high yields of pure cellulose materials in a short time with minimal resources, and pioneering work has shown that genetic engineering in these strains is possible and can be used to modify the material and its production. To accelerate synthetic biology progress in these bacteria, we introduce here the Komagataeibacter tool kit (KTK), a standardised modular cloning system based on Golden Gate DNA assembly that allows DNA parts to be combined to build complex multigene constructs expressed in bacteria from plasmids. Working in Komagataeibacter rhaeticus, we describe basic parts for this system, including promoters, fusion tags and reporter proteins, before showcasing how the assembly system enables more complex designs. Specifically, we use KTK cloning to reformat the Escherichia coli curli amyloid fibre system for functional expression in K. rhaeticus, and go on to modify it as a system for programming protein secretion from the cellulose producing bacteria. With this toolkit, we aim to accelerate modular synthetic biology in these bacteria, and enable more rapid progress in the emerging ELMs community.

  • Journal article
    Kondor A, Santmarti A, Mautner A, Williams D, Bismarck A, Lee K-Yet al., 2021,

    On the BET surface area of nanocellulose determined using volumetric, gravimetric and chromatographic adsorption methods

    , Frontiers in Chemical Engineering, Vol: 3, Pages: 1-12, ISSN: 2673-2718

    Volumetric N2 adsorption at –196 °C is generally accepted as “gold standard” for estimating the Brunauer-Emmet-Teller (BET) surface area of nanocellulose. It is unclear however, whether the BET surface area of nanocellulose obtained at such low temperatures and pressures is meaningful at an absolute sense, as nanocellulose is used at ambient temperature and pressure. In this work, a systematic evaluation of the BET surface area of nanocellulose using a highly crystalline bacterial cellulose (BC) as model nanocellulose was undertaken to achieve a comprehensive understanding of the limitations of BET method for nanocellulose. BET surface area obtained using volumetric N2 adsorption at –196 °C was compared with the BET surface area acquired from gravimetric experiments using n-octane adsorption measured using dynamic vapour sorption (DVS) and n-octane adsorption determined by inverse gas chromatography (iGC), both at 25 °C. It was found that the BET surface area calculated from volumetric N2 adsorption data was 25% lower than that of n-octane adsorption at 25 °C obtained using DVS and iGC adsorption methods. These results supported the hypothesis that the BET surface area of nanocellulose is both a molecular scale (N2 vs n-octane, molecular cross section of 0.162 nm2 vs 0.646 nm2) and temperature (–196 °C vs 25 °C) dependent property. This study also demonstrates the importance of selecting appropriate BET pressure range based on established criteria and would suggest that the room temperature gravimetric measurement is more relevant for many nanocellulose applications.

  • Journal article
    Yang Y, Wloch D, Lee K-Y, 2021,

    TEMPO-oxidised nanocellulose hydrogels and self-standing films derived from bacterial cellulose nanopaper

    , RSC Advances: an international journal to further the chemical sciences, Vol: 11, Pages: 28352-28360, ISSN: 2046-2069

    Hydrogels derived from TEMPO-oxidised cellulose nanofibrils (TOCNs) are not robust and inherently water unstable if theTOCNs are not crosslinked or coated with a water-swellable polymer. Furthermore, the manufacturing of self-standing TOCNfilms is still a challenge due to the small TOCN diameter and viscosifying effect. Here, we report the TEMPO-mediatedoxidation of bacterial cellulose (BC) nanopaper as a route to produce robust and water stable TOCN hydrogel without theneed for additional additives or crosslinking steps, as well as self-standing TOCN films without the need for vacuum filtrationor slow-drying of TOCN suspension. Pristine BC pellicle was first press-dried into a dried and well-consolidated BC nanopaper,followed by TEMPO-oxidation at various NaClO concentrations. The oxidation reaction introduced carboxylate moieties ontoexposed BC nanofibrils within the nanopaper network structure. This then led to the swelling of the nanopaper into ahydrogel. A swelling ratio of up to 100 times the original thickness of BC nanopaper was observed upon TEMPO-oxidation.The water retention value of the TEMPO-oxidised BC hydrogels was also found to increase with increasing carboxylatecontent. These TEMPO-oxidised BC hydrogels were found to be robust and water-stable, even under prolonged (>1 month)magnetic stirring in water. We further showed that high grammage self-standing TOCN films (100 g m-2) can be fabricatedas simple as press-drying a water stable TEMPO-oxidised BC hydrogels without the need of vacuum-assisted filtration orslow-drying, which is typically the rate-limiting step in the manufacturing of self-standing TOCN films.

  • Journal article
    Caro-Astorga J, Walker KT, Herrera N, Lee K-Y, Ellis Tet al., 2021,

    Bacterial cellulose spheroids as building blocks for 3D and patterned living materials and for regeneration.

    , Nature Communications, Vol: 12, Pages: 1-9, ISSN: 2041-1723

    Engineered living materials (ELMs) based on bacterial cellulose (BC) offer a promising avenue for cheap-to-produce materials that can be programmed with genetically encoded functionalities. Here we explore how ELMs can be fabricated in a modular fashion from millimetre-scale biofilm spheroids grown from shaking cultures of Komagataeibacter rhaeticus. Here we define a reproducible protocol to produce BC spheroids with the high yield bacterial cellulose producer K. rhaeticus and demonstrate for the first time their potential for their use as building blocks to grow ELMs in 3D shapes. Using genetically engineered K. rhaeticus, we produce functionalized BC spheroids and use these to make and grow patterned BC-based ELMs that signal within a material and can sense and report on chemical inputs. We also investigate the use of BC spheroids as a method to regenerate damaged BC materials and as a way to fuse together smaller material sections of cellulose and synthetic materials into a larger piece. This work improves our understanding of BC spheroid formation and showcases their great potential for fabricating, patterning and repairing ELMs based on the promising biomaterial of bacterial cellulose.

  • Journal article
    Kontturi KS, Lee K-Y, Jones MP, Sampson WW, Bismarck A, Kontturi Eet al., 2021,

    Influence of biological origin on the tensile properties of cellulose nanopapers

    , Cellulose, Vol: 28, Pages: 6619-6628, ISSN: 0969-0239

    Cellulose nanopapers provide diverse, strong and lightweight templates prepared entirely from sustainable raw materials, cellulose nanofibers (CNFs). Yet the strength of CNFs has not been fully capitalized in the resulting nanopapers and the relative influence of CNF strength, their bonding, and biological origin to nanopaper strength are unknown. Here, we show that basic principles from paper physics can be applied to CNF nanopapers to illuminate those relationships. Importantly, it appeared that ~ 200 MPa was the theoretical maximum for nanopapers with random fibril orientation. Furthermore, we demonstrate the contrast in tensile strength for nanopapers prepared from bacterial cellulose (BC) and wood-based nanofibrillated cellulose (NFC). Endemic amorphous polysaccharides (hemicelluloses) in NFC act as matrix in NFC nanopapers, strengthening the bonding between CNFs just like it improves the bonding between CNFs in the primary cell wall of plants. The conclusions apply to all composites containing non-woven fiber mats as reinforcement.

  • Journal article
    Gaduan AN, Solhi L, Kontturi E, Lee K-Yet al., 2021,

    From micro to nano: polypropylene composites reinforced with TEMPO-oxidised cellulose of different fibre widths

    , Cellulose, Vol: 28, Pages: 2947-2963, ISSN: 0969-0239

    TEMPO-oxidised cellulose fibres are often explored as nano-reinforcement for polymers. However, it is unclear whether micrometre-sized TEMPO-oxidised cellulose fibres also possess similar reinforcing potential. In this work, we report the mechanical response of polypropylene (PP) composites reinforced with TEMPO-oxidised cellulose (TOC) of different fibre widths. Micrometre-sized TOC fibres (TOCF) containing sodium carboxylate (TOCF-Na) and free hydroxyl (TOCF-H) groups, as well as nano-sized TOC nanofibrils (TOCN) were produced from dissolving pulp and incorporated into PP matrix via melt-extrusion. It was found that model PP composites containing micrometre-sized TOCF-Na and TOCF-H possessed the highest tensile modulus of up to 2.5 GPa; 40% improvement over neat PP and 30% increase over PP/TOCN composite. No significant differences in the tensile strength of PP/TOCF-Na and PP/TOCF-H composites were observed when compared to neat PP. The incorporation of nano-sized TOCN into PP however, led to a 6% decrease in tensile strength. Single-edge notched beam fracture toughness test further showed that PP/TOCN composite possessed the lowest fracture toughness of 2.52 MPa m1/2; a decrease of 18% over PP reinforced with micrometre-sized TOCF-Na and TOCF-H. Our study shows that micrometre-sized TOCFs serve as better reinforcement for polymers compared to nano-sized TOCN. This is attributed to the better dispersion of TOCF in the PP matrix. Furthermore, the presence of surface microfibrillation on TOCFs also enhanced the quality of the TOCF-PP interface through mechanical interlocking and local stiffening of the PP matrix.

  • Journal article
    Santmarti A, Tammelin T, Lee K-Y, 2020,

    Prevention of interfibril hornification by replacing water in nanocellulose gel with low molecular weight liquid poly(ethylene glycol)

    , Carbohydrate Polymers, Vol: 250, Pages: 1-9, ISSN: 0144-8617

    Nanocellulose is typically stored and transported as a gel with a nominal solid content of up to 5 wt.-% to avoid interfibril hornification, i.e. the formation of irreversible hydrogen bonds between adjacent nanocellulose upon drying, which makes nanocellulose not cost-effective. In this work, we report the use of low molecular weight liquid poly(ethylene glycol) (PEG-200) as a replacement for the water phase in nanocellulose aqueous gel. Our results indicated that nanocellulose can be stored in PEG-200 at a solid content of up to 70 wt.-% without interfibril hornification, even when exposed to the ambient environment. This is due to the low vapour pressure and high boiling point of PEG-200. ATR-FTIR and ζ-potential measurements confirmed that PEG-200 can be easily washed out from the nanocellulose as PEG-200 is water miscible. Using PEG-200 as a replacement for the water phase in nanocellulose aqueous gel could improve the cost-efficiency of nanocellulose storage and transportation. The tensile properties of the cellulose nanopaper prepared from the various never-dried and once-dried nanocellulose are also discussed in this work.

  • Journal article
    Vilchez V, Dieckmann E, Tammelin T, Cheeseman C, Lee K-Yet al., 2020,

    Upcycling Poultry Feathers with (Nano)cellulose: Sustainable Composites Derived from Nonwoven Whole Feather Preforms

    , ACS Sustainable Chemistry & Engineering, Vol: 8, Pages: 14263-14267, ISSN: 2168-0485
  • Journal article
    Santmarti A, Liu HW, Herrera N, Lee K-Yet al., 2020,

    Anomalous tensile response of bacterial cellulose nanopaper at intermediate strain rates

    , Scientific Reports, Vol: 10, ISSN: 2045-2322

    Nanocellulose network in the form of cellulose nanopaper is an important material structure and its time-dependent mechanical response is crucial in many of its potential applications. In this work, we report the influences of grammage and strain rate on the tensile response of bacterial cellulose (BC) nanopaper. BC nanopaper with grammages of 20, 40, 60 and 80 g m−2 were tested in tension at strain rates ranging from 0.1% s−1 to 50% s−1. At strain rates ≤ 2.5% s−1, both the tensile modulus and strength of the BC nanopapers stayed constant at ~ 14 GPa and ~ 120 MPa, respectively. At higher strain rates of 25% s−1 and 50% s−1 however, the tensile properties of the BC nanopapers decreased significantly. This observed anomalous tensile response of BC nanopaper is attributed to inertial effect, in which some of the curled BC nanofibres within the nanopaper structure do not have enough time to uncurl before failure at such high strain rates. Our measurements further showed that BC nanopaper showed little deformation under creep, with a secondary creep rate of only ~ 10–6 s−1. This stems from the highly crystalline nature of BC, as well as the large number of contact or physical crosslinking points between adjacent BC nanofibres, further reducing the mobility of the BC nanofibres in the nanopaper structure.

  • Journal article
    Song W, Magid A, Li D, Lee K-Yet al., 2020,

    Application of recycled carbon-fibre-reinforced polymers as reinforcement for epoxy foams

  • Journal article
    Gregory GL, Sulley GS, Carrodeguas LP, Chen TTD, Santmarti A, Terrill NJ, Lee K-Y, Williams CKet al., 2020,

    Triblock polyester thermoplastic elastomers with semi-aromatic polymer end blocks by ring-opening copolymerization

    , Chemical Science, Vol: 11, Pages: 6567-6581, ISSN: 2041-6520

    Thermoplastic elastomers benefit from high elasticity and straightforward (re)processability; they are widely used across a multitude of sectors. Currently, the majority derive from oil, do not degrade or undergo chemical recycling. Here a new series of ABA triblock polyesters are synthesized and show high-performances as degradable thermoplastic elastomers; their composition is poly(cyclohexene-alt-phthalate)-b-poly(ε-decalactone)-b-poly(cyclohexene-alt-phthalate) {PE–PDL–PE}. The synthesis is accomplished using a zinc(II)/magnesium(II) catalyst, in a one-pot procedure where ε-decalactone ring-opening polymerization yielding dihydroxyl telechelic poly(ε-decalatone) (PDL, soft-block) occurs first and, then, addition of phthalic anhydride/cyclohexene oxide ring-opening copolymerization delivers semi-aromatic polyester (PE, hard-block) end-blocks. The block compositions are straightforward to control, from the initial monomer stoichiometry, and conversions are high (85–98%). Two series of polyesters are prepared: (1) TBPE-1 to TBPE-5 feature an equivalent hard-block volume fraction (fhard = 0.4) and variable molar masses 40–100 kg mol−1; (2) TBPE-5 to TBPE-9 feature equivalent molar masses (∼100 kg mol−1) and variable hard-block volume fractions (0.12 < fhard < 0.4). Polymers are characterized using spectroscopies, size-exclusion chromatography (SEC), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). They are amorphous, with two glass transition temperatures (∼−51 °C for PDL; +138 °C for PE), and block phase separation is confirmed using small angle X-ray scattering (SAXS). Tensile mechanical performances reveal thermoplastic elastomers (fhard < 0.4 and N > 1300) with linear stress–strain relationships, high ultimate tensile strengths (σb = 1–5 MPa), very high elongations at break (&ep

  • Journal article
    Nawawi WMFW, Lee K-Y, Kontturi E, Bismarck A, Mautner Aet al., 2020,

    Surface properties of chitin-glucan nanopapers from Agaricus bisporus

    , International Journal of Biological Macromolecules, Vol: 148, Pages: 677-687, ISSN: 0141-8130

    The structural component of fungal cell walls comprises of chitin covalently bonded to glucan; this constitutes a native composite material (chitin-glucan, CG) combining the strength of chitin and the toughness of glucan. It has a native nano-fibrous structure in contrast to nanocellulose, for which further nanofibrillation is required. Nanopapers can be manufactured from fungal chitin nanofibrils (FChNFs). FChNF nanopapers are potentially applicable in packaging films, composites, or membranes for water treatment due to their distinct surface properties inherited from the composition of chitin and glucan. Here, chitin-glucan nanofibrils were extracted from common mushroom (Agaricus bisporus) cell walls utilizing a mild isolation procedure to preserve the native quality of the chitin-glucan complex. These extracts were readily disintegrated into nanofibre dimensions by a low-energy mechanical blending, thus making the extract dispersion directly suitable for nanopaper preparation using a simple vacuum filtration process. Chitin-glucan nanopaper morphology, mechanical, chemical, and surface properties were studied and compared to chitin nanopapers of crustacean (Cancer pagurus) origin. It was found that fungal extract nanopapers had distinct physico-chemical surface properties, being more hydrophobic than crustacean chitin.

  • Journal article
    Mautner A, Nawawi WMFW, Lee K-Y, Bismarck Aet al., 2020,

    High porosity cellulose nanopapers as reinforcement in multi-layer epoxy laminates

    , Composites Part A: Applied Science and Manufacturing, Vol: 131, Pages: 1-9, ISSN: 1359-835X

    Utilizing high-performance cellulose nanopapers as 2D-reinforcement for polymers allows for realizing high-loading-fraction (80 vol-%), high-performance (strength > 150 MPa, modulus > 10 GPa) laminated nanopaper reinforced epoxy composites. Such cellulose nanopapers are inherently dense, which renders them difficult to be impregnated with the epoxy-resin. High-porosity nanopapers facilitate better resin impregnation, truly utilizing the properties of single cellulose nanofibres instead of the nanofibre network. We report the use of high-porosity (74%) but low strength and modulus bacterial cellulose (BC) nanopapers, prepared from BC-in-ethanol dispersion, as reinforcement for epoxy-resin. High-porosity nanopapers allowed for full impregnation of the BC-nanopapers with epoxy-resin. The resulting BC-reinforced epoxy-laminates possessed high tensile modulus (9 GPa) and strength (100 MPa) at a BC loading of 30 vol-%, resulting from very low void-fraction (3 vol-%) of these papregs compared to conventional nanopaper-laminates (10+ vol.-%). Better resin impregnation of less dense nanocellulose networks allowed for maximum utilization of stiffness/strength of cellulose nanofibrils.

  • Journal article
    Sulley GS, Gregory GL, Chen TTD, Carrodeguas LP, Trott G, Santmarti A, Lee K-Y, Terrill NJ, Williams CKet al., 2020,

    Switchable catalysis improves the properties of CO2-derived polymers: poly(cyclohexene carbonate-b-epsilon-decalactone-b-cyclohexene carbonate) adhesives, elastomers, and toughened plastics

    , Journal of the American Chemical Society, Vol: 142, Pages: 4367-4378, ISSN: 0002-7863

    Carbon dioxide/epoxide copolymerization is an efficient way to add value to waste CO2 and to reduce pollution in polymer manufacturing. Using this process to make low molar mass polycarbonate polyols is a commercially relevant route to new thermosets and polyurethanes. In contrast, high molar mass polycarbonates, produced from CO2, generally under-deliver in terms of properties, and one of the most widely investigated, poly(cyclohexene carbonate), is limited by its low elongation at break and high brittleness. Here, a new catalytic polymerization process is reported that selectively and efficiently yields degradable ABA-block polymers, incorporating 6–23 wt % CO2. The polymers are synthesized using a new, highly active organometallic heterodinuclear Zn(II)/Mg(II) catalyst applied in a one-pot procedure together with biobased ε-decalactone, cyclohexene oxide, and carbon dioxide to make a series of poly(cyclohexene carbonate-b-decalactone-b-cyclohexene carbonate) [PCHC-PDL-PCHC]. The process is highly selective (CO2 selectivity >99% of theoretical value), allows for high monomer conversions (>90%), and yields polymers with predictable compositions, molar mass (from 38–71 kg mol–1), and forms dihydroxyl telechelic chains. These new materials improve upon the properties of poly(cyclohexene carbonate) and, specifically, they show good thermal stability (Td,5 ∼ 280 °C), high toughness (112 MJ m–3), and very high elongation at break (>900%). Materials properties are improved by precisely controlling both the quantity and location of carbon dioxide in the polymer chain. Preliminary studies show that polymers are stable in aqueous environments at room temperature over months, but they are rapidly degraded upon gentle heating in an acidic environment (60 °C, toluene, p-toluene sulfonic acid). The process is likely generally applicable to many other lactones, lactides, anhydrides, epoxides, and heterocumulenes and sets the s

  • Journal article
    Santmarti A, Zhang H, Lappalainen T, Lee K-Yet al., 2020,

    Cellulose nanocomposites reinforced with bacterial cellulose sheets prepared from pristine and disintegrated pellicle

    , Composites Part A: Applied Science and Manufacturing, Vol: 130, Pages: 1-9, ISSN: 1359-835X

    BC sheets can be prepared in two forms: direct press-drying of the as-synthesised BC pellicle or disintegrating the BC pellicle to create a homogenous BC-in-water suspension prior to producing the BC sheet. We found that BC sheet prepared from direct press-drying of pristine pellicle was more homogeneous due to its better BC network formation and possessed higher specific surface area (46 g m−2), better resin impregnation and mechanical properties compared to its disintegrated pellicle counterpart (21 g m−2). BC-poly(acrylated epoxidised soybean oil) (polyAESO) nanocomposites consisting of BC sheet prepared from pristine pellicle was optically transparent whilst BC-polyAEO nanocomposites consisting of BC sheet prepared from disintegrated pellicle was opaque. Whilst the tensile properties of BC-polyAESO nanocomposites from pristine pellicle were higher, the fracture toughness of BC-polyAESO composite consisting of BC sheet from disintegrated pellicle was better. The lack of resin impregnation in BC-polyAESO from disintegrated pellicle led to a laminated structure, which utilised the fracture toughness of BC sheet effectively.

  • Journal article
    Nawawi WMFBW, Jones M, Murphy RJ, Lee K-Y, Kontturi E, Bismarck Aet al., 2020,

    Nanomaterials derived from fungal sources-is It the new hype?

    , Biomacromolecules, Vol: 21, Pages: 30-55, ISSN: 1525-7797

    Greener alternatives to synthetic polymers are constantly being investigated and sought after. Chitin is a natural polysaccharide that gives structural support to crustacean shells, insect exoskeletons, and fungal cell walls. Like cellulose, chitin resides in nanosized structural elements that can be isolated as nanofibers and nanocrystals by various top-down approaches, targeted at disintegrating the native construct. Chitin has, however, been largely overshadowed by cellulose when discussing the materials aspects of the nanosized components. This Perspective presents a thorough overview of chitin-related materials research with an analytical focus on nanocomposites and nanopapers. The red line running through the text emphasizes the use of fungal chitin that represents several advantages over the more popular crustacean sources, particularly in terms of nanofiber isolation from the native matrix. In addition, many β-glucans are preserved in chitin upon its isolation from the fungal matrix, enabling new horizons for various engineering solutions.

  • Book chapter
    Jiang Q, Lee K, Bismarck A, 2020,

    Foam templating: A greener route to porous polymers

    , ACS Symposium Series, Pages: 99-118

    A simple kitchen mixer and skills to whip cream can be useful to manufacture highly functional polymer foams with control over their structures. In the 1930s, researchers began to whip or inject gas into monomers or polymer suspensions to produce liquid foams, which served as templates to be solidified to polymer foams. Besides the “simplicity” of the foam templating method, its actual advantage as compared to widely used blown polymer foams is the nonessential need of physical and chemical blowing agents, resulting in a lower raw material cost, less involved chemistry, lower safety and health risk during production and a reduced impact on the environment. Compared to other templating methods, such as emulsion templating, which require sacrificial materials serving as templates, liquid foams with bubbles as templates are superior from a material processing perspective because they require no further materials or energy for template removal. A challenging step in foam templating is to create a stable liquid foam containing building blocks for subsequent solidification; when using air as an internal phase, the choice of materials in the liquid phase to create a stable colloidal system is restricted. In this chapter, we review previous work on foam templating with a focus on porous materials produced therefrom, including macroporous thermoplastic, thermosetting polymers, hydrogels, biobased materials and polymer composites. We aim to show that foam templating is a greener than any other templating methods, such as emulsion templating and particulate leaching, and versatile foaming process and to encourage researchers to conduct both fundamental and applied research to push the boundaries of this technology further.

  • Journal article
    Song W, Konstantellos G, Li D, Lee K-Yet al., 2019,

    Short carbon fibre-reinforced epoxy foams with isotropic cellular structure and anisotropic mechanical response produced from liquid foam templates

    , Composites Science and Technology, Vol: 184, Pages: 1-9, ISSN: 0266-3538

    In this work, we show that mechanically anisotropic short carbon fibre (sCF)-reinforced epoxy foams with an isotropic cellular structure can be fabricated from liquid foam templates. Short carbon fibres were mechanically frothed in an uncured liquid epoxy resin to produce an air-in-resin liquid foam template, followed by subsequent polymerisation. Fracture toughness test showed that the incorporation of short carbon fibres into the epoxy foams led to a significant increase in their critical stress intensity factors. It was also observed that neat epoxy foams failed catastrophically whilst sCF-reinforced epoxy foams failed in a progressive manner. Compression test further showed that the in-plane compressive moduli of the mechanically frothed sCF-reinforced epoxy foams were significantly higher than their out-of-plane compressive moduli, signifying an anisotropic mechanical response. This anisotropic mechanical response stemmed from the radial flow generated by the high intensity mechanical frothing process, facilitating the preferential orientation of the added short carbon fibres in-plane whilst the entrained air bubbles during the mechanical frothing process were in equilibrium with the surrounding uncured liquid epoxy resin, resulting in an epoxy foam with an isotropic (spherical) cellular structure.

  • Journal article
    Mishnaevsky L, Mikkelsen LP, Gaduan AN, Lee KY, Madsen Bet al., 2019,

    Nanocellulose reinforced polymer composites: Computational analysis of structure-mechanical properties relationships

    , Composite Structures, Vol: 224, ISSN: 0263-8223

    Structure-mechanical properties relationships of nanocellulose reinforced polymer composites are studied in computational experiments. A code for the generation of 3D unit cell finite element models of nanocellulose reinforced polymers with “snake”-shaped nanocellulose fibrils is developed. The code allows the generation of pre-defined nanocomposites structures, with varied angles between nanocellulose snakes segments and hydrogen bonds between nanocellulose fibrils. In a series of computational studies, it is demonstrated that the nanocellulose reinforcement leads to higher stiffness of the matrix polymer, but makes it more brittle.

  • Journal article
    Suwan K, Waramit S, Przystal J, Stoneham C, Bentayebi K, Asavarut P, Chongchai A, Pothachareon P, Lee K-Y, Topanurak S, Smith T, Gelovani J, Sidman R, Pasqualini R, Arap W, Hajitou Aet al., 2019,

    Next-generation of targeted AAVP vectors for systemic transgene delivery against cancer

    , Proceedings of the National Academy of Sciences of USA, Vol: 116, Pages: 18571-18577, ISSN: 0027-8424

    Bacteriophage (phage) have attractive advantages as delivery sys-tems compared to mammalian viruses, but have been consideredpoor vectors because they lack evolved strategies to confrontand overcome mammalian cell barriers to infective agents. Wereasoned that improved efficacy of delivery might be achievedthrough structural modification of the viral capsid to avoid pre-and post-internalization barriers to mammalian cell transduction.We generated multifunctional hybrid AAV/phage (AAVP) particlesto enable simultaneous display of targeting ligands on the phage’sminor pIII proteins and also degradation-resistance motifs on thevery numerous pVIII coat proteins. This genetic strategy of directedevolution, bestows a next-generation of AAVP particles that fea-ture resistance to fibrinogen adsorption or neutralizing antibodies,and ability to escape endolysosomal degradation. This results insuperior gene transfer efficacyin vitroand also in preclinicalmouse models of rodent and human solid tumors. Thus, the uniquefunctions of our next-generation AAVP particles enable improvedtargeted gene delivery to tumor cells.

  • Journal article
    Karim Z, Svedberg A, Lee K-Y, Khan MJet al., 2019,

    Processing-atructure-property correlation understanding of microfibrillated cellulose based dimensional structures for ferric ions removal

    , Scientific Reports, Vol: 9, Pages: 1-12, ISSN: 2045-2322

    In this research article, wood based microfibrillated cellulose (MFC) was studied to gain a better understanding of the process of dependent network formation. Networking potential and obtained properties of the produced dimensional structures could be controlled using opted processing routes. The fabricated dimensional structure, using freeze-drying (FD) is a highly open and porous network (98% porosity) compared to slightly tight, dense and less porous network produced after pressing at 200kN (96% porosity), followed by vacuum-filtered (VF) networks (33% porosity). The porosity (17%) was further decreased when the casting (CS) method was used, further producing a highly dense and compressed network. High water flux (180.8 ± 11 L/m2h) of pressed freeze-dried (PFD) followed by vacuum-filtered (VF) (11.4 ± 1.9 L/m2h) and casting CS (0.7 ± 0.01 L/m2h) were calculated using device. Furthermore, increased water flux (1.4 fold) of Experimental Paper Machine (XPM) based structures was reported in comparison with CS structures. Pore-sized distribution and surface area were measured using Hg porosimetry; they showed an average pore size of 16.5 μm for FD, followed by PFD (8.2 μm) structures. A 27-fold decrease in average pore-size was observed for CS structure in comparison with the FD structures. Highest tensile strength (87 ± 21 MPa) was recorded for CS structures, indicating a more highly compacted network formation compared to VF (82 ± 19 MPa) and PFD (1.6 ± 0.06 MPa). Furthermore, an attempt was made to upscale the VF structures using traditional paper making approach on XMP. Improved tensile strength (73 ± 11 MPa) in machine produced structures is due to alignment of fibers towards machine direction compared to cross directional (43 ± 9 MPa)

  • Journal article
    Dieckmann E, Eleftheriou K, Audic T, Lee KY, Sheldrick L, Cheeseman Cet al., 2019,

    New sustainable materials from waste feathers: Properties of hot-pressed feather/cotton/bi-component fibre boards

    , Sustainable Materials and Technologies, Vol: 20, ISSN: 2214-9937

    Feathers from poultry are an abundant, globally available waste. The current beneficial reuse for feathers involves autoclaving them to produce feather meal, an animal feed with low economic value. This paper reports on the production and performance of new feather-derived materials. These have potential to provide a higher value application for waste feathers. Feather fibres, cotton fibres and polyethylene/polypropylene bi-component fibres (blended 55:20:25 by weight) have been air-laid to form 20 mm thick non-woven pre-forms with a density of 0.14 g cm −2 . These were then hot pressed to produce materials with significantly higher density and improved properties. Optimum materials were formed by hot pressing between 150 and 160 °C at 6 MPa for 1 min. Lower temperatures resulted in poor fibre bonding and fibre pull-out during fracture. Higher temperatures caused thermal degradation of the feather fibres. The optimum feather fibre boards with a density of 0.77 g/cm 3 , corresponding to 31.3% porosity, had tensile strengths of 17.9 MPa a tensile modulus of 1.74 GPa and an elongation at fracture of 5.9%. These samples exhibited fibre fracture during tensile testing. Feather fibre boards have similar tensile strength, density and Young's modulus to particleboard, organic resin particleboard and flake board. Quantitative estimates of the economic and environmental benefits from using feather fibres to form feather fibre boards are discussed. The research advances sustainability by providing a new potential circular economy outlet for waste feathers and is part of on-going research to develop novel applications that exploit the unique properties of feathers.

  • Journal article
    Santmarti A, Teh JW, Lee K-Y, 2019,

    Transparent poly(methyl methacrylate) composites based on bacterial cellulose nanofibre networks with improved fracture resistance and impact strength

    , ACS Omega, Vol: 4, Pages: 9896-9903, ISSN: 2470-1343

    Cellulose nanofibers are often explored as biobased reinforcement for the production of high-performance composite materials. In this work, we fabricated transparent poly(methyl methacrylate) (PMMA) composites consisting of two-dimensional and three-dimensional bacterial cellulose (BC) nanofiber networks. Three different composite designs consisting of 1 vol % BC loading were fabricated and studied: (i) composites with a three-dimensional BC nanofiber network embedded uniformly throughout the PMMA matrix; (ii) sandwich-structured construction consisting of three-dimensional BC–PMMA sandwiched between two neat PMMA sheets; and (iii) dried and well-consolidated two-dimensional BC nanofiber network embedded in a PMMA matrix. All fabricated model BC–PMMA composites were found to be optically transparent, but PMMA composites consisting of the two-dimensional BC nanofiber network possessed higher light transmittance (73% @550 nm) compared to the three-dimensional BC nanofiber network counterparts (63% @550 nm). This is due to the higher specific surface area of the three-dimensional BC nanofiber network, which led to more light scattering. Nevertheless, it was found that both two-dimensional and three-dimensional BC nanofiber networks serve as excellent stiffening agents for PMMA matrix, improving the tensile modulus of the resulting composites by up to 30%. However, no improvement in tensile strength was observed. The use of three-dimensional BC nanofiber network led to matrix embrittlement, reducing the tensile strain-at-failure, fracture resistance, and Charpy impact strength of the resulting BC–PMMA composites. When the BC nanofiber network was used as two-dimensional reinforcement, cracks were observed to propagate through the debonding of BC nanofiber network, leading to higher fracture toughness and Charpy impact strength. These novel findings could open up further opportunities in the design of novel optically transparent polymeric composite lami

  • Journal article
    Fazli Wan Nawawi WM, Lee KY, Kontturi E, Murphy RJ, Bismarck Aet al., 2019,

    Chitin nanopaper from mushroom extract: natural composite of nanofibers and glucan from a single biobased source

    , ACS Sustainable Chemistry and Engineering, Vol: 7, Pages: 6492-6496, ISSN: 2168-0485

    An isolation method with mild mechanical agitation and no acidic extraction step from a mushroom substrate resulted in chitin nanofibers (ChNFs) with large shares of retained glucans (50-65%). The subsequent chitin nanopapers exhibited exceptionally high tensile strengths of >200 MPa and moduli of ca. 7 GPa, which were largely attributed to the preserved glucans in the mixture, imparting a composite nature to the nanopapers. The isolation method for ChNFs is notably different from the conventional process with crustacean chitin sources that do not incorporate glucans and where an acidic extraction step for the removal of minerals must always be included.

  • Journal article
    Mohammed C, Mahabir S, Mohammed K, John N, Lee K-Y, Ward Ket al., 2019,

    Calcium Alginate Thin Films Derived from Sargassum natans for the Selective Adsorption of Cd2+, Cu2+, and Pb2+ Ions

    , Industrial & Engineering Chemistry Research, Vol: 58, Pages: 1417-1425, ISSN: 0888-5885

    The Caribbean has seen the influx of Sargassum, affecting the livelihood of communities. Sodium alginate extracted from Sargassum is known for its cross-linking properties, making the seaweed attractive as an adsorbent. Hence, the use of calcium alginate thin films can decrease the mass transfer resistance found in commonly used alginate beads, resulting in increased adsorption efficiency. This Article discusses the potential of calcium alginate thin films for Pb2+, Cu2+, and Cd2+ ion adsorption. Pb2+, Cu2+, and Cd2+ adsorption fitted the Langmuir isotherm well with capacities of 0.80, 0.10, and 0.02 mmol of metal/g, respectively, for Sargassum. Kinetic studies showed that the ions followed the pseudo-second-order model, elucidating that ion exchange governed adsorption. Furthermore, NMR characterization showed that G-block monomers influenced kinetic parameters and selectivity in the following order: Pb2+ > Cu2+ > Cd2+

  • Journal article
    Song W, Tagarielli VL, Lee KY, 2018,

    Enhancing the fracture resistance and impact toughness of mechanically frothed epoxy foams with hollow elastomeric microspheres

    , Macromolecular Materials and Engineering, Vol: 303, ISSN: 1438-7492

    Nonporous elastomeric particles are often employed to improve the toughness of brittle epoxy foams but this also decreases their compressive strength and stiffness. Herein, a novel strategy utilizing hollow elastomeric microspheres as toughening agent for epoxy foams is presented. The addition of 0.5 wt.% hollow elastomeric microspheres into epoxy foam leads to a 15% increase in critical stress intensity factor (K1c) to 0.38 MPa m0.5and 33% increase in Charpy impact strength (acU) to 1.05 kJ m−2, respectively, compared to unfilled epoxy foam (K1c = 0.33 MPa m0.5and acU= 0.79 kJ m−2). However, a further increase in the hollow elastomeric microsphere concentration to 1.0 wt.% leads to microsphere agglomeration, which reduces both K1cand acUto 0.35 MPa m0.5and 0.93 kJ m−2, respectively. Nevertheless, the added hollow elastomeric microspheres do not lead to a reduction in the quasi-static compressive properties of the epoxy foams.

  • Journal article
    Hervy M, Bock F, Lee KY, 2018,

    Thinner and better: (Ultra-)low grammage bacterial cellulose nanopaper-reinforced polylactide composite laminates

    , Composites Science and Technology, Vol: 167, Pages: 126-133, ISSN: 0266-3538

    One of the rate-limiting steps in the large-scale production of cellulose nanopaper-reinforced polymer composites is the time consuming dewatering step to produce the reinforcing cellulose nanopapers. In this work, we show that the dewatering time of bacterial cellulose (BC)-in-water suspension can be reduced by reducing the grammage of BC nanopaper to be produced. The influence of BC nanopaper grammage on the tensile properties of BC nanopaper-reinforced polylactide (PLLA) composites is also investigated in this work. BC nanopaper with grammages of 5, 10, 25 and 50 g m−2 were produced and it was found that reducing the grammage of BC nanopaper from 50 g m−2 to 5 g m−2 led to a three-fold reduction in the dewatering time of BC-in-water suspension. The porosity of the BC nanopapers, however, increased with decreasing BC nanopaper grammage. While the tensile properties of BC nanopapers were found to decrease with decreasing BC nanopaper grammage, no significant difference in the reinforcing ability of BC nanopaper with different grammages for PLLA was observed. All PLLA composite laminates reinforced with BC nanopapers possessed similar tensile modulus of 10.5–11.8 GPa and tensile strength of 95–111 MPa, respectively, at a BC loading fraction  = 39–53 vol.-%, independent of the grammage and tensile properties of the reinforcing BC nanopaper.

  • Journal article
    Mohammed A, Bissoon R, Bajnath E, Mohammed K, Lee T, Bissram M, John N, Jalsa NK, Lee KY, Ward Ket al., 2018,

    Multistage extraction and purification of waste Sargassum natans to produce sodium alginate: an optimization approach

    , Carbohydrate Polymers, Vol: 198, Pages: 109-118, ISSN: 0144-8617

    Sargassum in the Caribbean region has affected the livelihood of several coastal communities due to the influx of large quantities of the seaweed in recent times. This article seeks to explore how waste Sargassum natans can be utilized to produce sodium alginate. The novelty in this research lies in the optimization process, whereby multistage extraction and precipitation were investigated over commonly used single stage processing, in an effort to maximize both yield and purity. The results showed that a maximum yield of 19% was observed after 1 stage, while the purity was 74% after 4 stages. In addition, optimization of the multistage precipitation process using the Global Optimization Toolbox in MATLAB R2017b provided a novel model which indicated that a compromise between the maximum purity and yield can be obtained at 3 stages; 71–74% and 12–16% respectively. Furthermore, characterization was done using FTIR and NMR, with results comparable to a commercial sodium alginate brand, giving absorption bands at 1610 cm−1and 1395 cm-1and an M/G ratio of 0.51 respectively.

  • Journal article
    Narducci F, Lee K, Pinho ST, 2018,

    Realising damage-tolerant nacre-inspired CFRP

    , Journal of the Mechanics and Physics of Solids, Vol: 116, Pages: 391-402, ISSN: 0022-5096

    Inthiswork,anacre-inspiredCarbonFibreReinforcedPolymer(CFRP)compositeis designed,synthesisedandtested. Analyticalandnumericalmodelsareusedtodesign a tiled micro-structure, mimicking the staggered arrangement of ceramic platelets in nacreandexploitinggeometricalinterlocksforcrackdeflectionanddamagediffusion. The designed pattern of tiles is then laser-engraved in the laminate plies. In order to increase the damage-spreading capability of the material, a thin layer of poly(lactic acid) (PLA) is film-cast on the interlaminar region, both as a continuous film and as a pattern of fractal-shaped patches. Three-point bending tests show how the nacre-like micro-structure succeeds in deflecting cracks, with damage diffusion being significantly improved by the addition of PLA at the interface between tiles. It is observed that a texture of discontinuous fractal-shaped PLA patches can increase damage diffusion, by promoting the unlocking of tiles whilst preserving the interface strength.

  • Journal article
    Hervy M, Blaker JJ, Braz AL, Lee KYet al., 2018,

    Mechanical response of multi-layer bacterial cellulose nanopaper reinforced polylactide laminated composites

    , Composites Part A: Applied Science and Manufacturing, Vol: 107, Pages: 155-163, ISSN: 1359-835X

    In this study, we investigated the mechanical response of polylactide (PLLA) reinforced with multiple layers of BC nanopaper. Laminated composites consisting of 1, 3, 6 and 12 sheet(s) of BC nanopaper were produced. It was observed that increasing the number of BC nanopaper led to an increase in the porosity of the resulting BC nanopaper-reinforced PLLA laminated composites. The tensile moduli of the laminated composites were found to be ∼12.5 – 13.5 GPa, insensitive to the number of sheets of BC nanopaper in the composites. However, the tensile strength of the laminated composites decreased by 21% (from 121 MPa to 95 MPa) when the number of reinforcing BC nanopaper sheets increased from 1 to 12 sheets. This was attributed to the presence and severity of the scale-induced defects increased with increasing BC nanopaper sheets in the PLLA laminated composites.

  • Journal article
    Narducci F, Lee KY, Pinho ST, 2018,

    Interface micro-texturing for interlaminar toughness tailoring: a film-casting technique

    , Composites Science and Technology, Vol: 156, Pages: 203-214, ISSN: 0266-3538

    In this work, we developed a film-casting technique to deposit thin (13 μm) layers of poly(lactic acid) (PLA) on the interface of carbon/epoxy prepregs, with the aim of increasing the interlaminar toughness. PLA patches with fractal shape were explored, based on preliminary results showing that the toughening effect increases when PLA is deposited at multiple scales simultaneously. Double Cantilever Beam (DCB) and 4-point End-Notched Flexure (4ENF) tests showed an increase in interlaminar toughness of, respectively, up to 80% for Mode I and 12% for Mode II. This is specially remarkable because the interface thickness is only 13 μm. Moreover, it was demonstrated that this technique can promote interaction between neighbouring layers where PLA has been cast, thus triggering fibre bridging and leading to a further enhancement of toughness.

  • Book chapter
    Santmarti A, Lee K, 2018,

    Crystallinity and Thermal Stability of Nanocellulose

    , Nanocellulose and Sustainability Production, Properties, Applications, and Case Studies, Editors: Lee, Publisher: Taylor and Francis / CRC Press, Pages: 67-86, ISBN: 9781498761031
  • Book
    Lee K-Y, 2018,

    Nanocellulose and Sustainability: Production, Properties, Applications, and Case Studies

    , Publisher: CRC Press/Taylor Francis, ISBN: 9781498761031
  • Journal article
    Mautner A, Mayer F, Hervy M, Lee K-Y, Bismarck Aet al., 2017,

    Better together: synergy in nanocellulose blends

    , Philosophical Transactions of the Royal Society A. Mathematical, Physical and Engineering Sciences, Vol: 376, ISSN: 1364-503X

    Cellulose nanopapers have gained significantattention in recent years as large-scale reinforcementfor high-loading cellulose nanocomposites, substratesfor printed electronics and filter nanopapers forwater treatment. The mechanical properties ofnanopapers are of fundamental importance forall these applications. Cellulose nanopapers cansimply be prepared by filtering a suspension ofnanocellulose, followed by heat consolidation. It wasalready demonstrated that the mechanical propertiesof cellulose nanopapers can be tailored by the finenessof the fibrils used or by modifying nanocellulosefibrils for instance by polymer adsorption, butnanocellulose blends remain underexplored. In thiswork, we show that the mechanical and physicalproperties of cellulose nanopapers can be tuned bycreating nanopapers from blends of various gradesof nanocellulose, i.e. (mechanically refined) bacterialcellulose or cellulose nanofibrils extracted fromnever-dried bleached softwood pulp by chemical andmechanical pre-treatments. We found that nanopapersmade from blends of two or three nanocellulosegrades show synergistic effects resulting in improvedstiffness, strength, ductility, toughness and physicalproperties.This article is part of a discussion meeting issue‘New horizons for cellulose nanotechnology’.

  • Journal article
    Kontturi KS, Biegaj K, Mautner A, Woodward RT, Wilson BP, Johansson L-S, Lee K-Y, Heng JYY, Bismarck A, Kontturi Eet al., 2017,

    Noncovalent Surface Modification of Cellulose Nanopapers by Adsorption of Polymers from Aprotic Solvents

    , LANGMUIR, Vol: 33, Pages: 5707-5712, ISSN: 0743-7463

    Basic adsorption of hydrophobic polymers from aprotic solvents was introduced as a platform technology to modify exclusively the surfaces of cellulose nanopapers. Dynamic vapor sorption demonstrated that the water vapor uptake ability of the nanopapers remained unperturbed, despite strong repellency to liquid water caused by the adsorbed hydrophobic polymer on the surface. This was enabled by the fact that the aprotic solvents used for adsorption did not swell the nanopaper unlike water that is generally applied as the adsorption medium in such systems. As case examples, the adsorptions of polystyrene (PS) and poly(trifluoroethylene) (PF3E) were followed by X-ray photoelectron spectroscopy and water contact angle measurements, backed up with morphological analysis by atomic force microscopy. The resulting nanopapers are useful in applications like moisture buffers where repellence to liquid water and ability for moisture sorption are desired qualities.

  • Book chapter
    Lee K, Daud NJ, 2017,

    Surface Modification of Nanocellulose

    , Handbook of Nanocellulose and Cellulose Nanocomposites, 2 Volume Set, Editors: Kargarzadeh, Ahmad, Thomas, Dufresne, Publisher: John Wiley & Sons, Pages: 101-122, ISBN: 9783527338665

    With its coverage of a wide variety of materials, important characterization tools and resulting applications, this is an essential reference for beginners as well as experienced researchers.

  • Journal article
    Hervy M, Santmarti A, Lahtinen P, Tammelin T, Lee Ket al., 2017,

    Sample geometry dependency on the measured tensile properties of cellulose nanopapers

    , Materials & Design, Vol: 121, Pages: 421-429, ISSN: 0261-3069

    Miniaturised test specimens are often used for the tensile testing of cellulose nanopapers as there are currently no standardised test geometries to evaluate their tensile properties. In this work, we report the influence of test specimen geometries on the measured tensile properties of plant-derived cellulose nanofibres (CNF) and microbially synthesised bacterial cellulose (BC) nanopapers. Four test specimen geometries were studied: (i) miniaturised dog bone specimen with 2 mm width, (ii) miniaturised rectangular specimen with 5 mm width, (iii) standard dog bone specimen with 5 mm width and (iv) standard rectangular specimen with 15 mm width. It was found that the tensile moduli of both CNF and BC nanopapers were not significantly influenced by the test specimen geometries if an independent strain measurement system (video extensometer) was employed. The average tensile strength of the cellulose nanopapers is also influenced by test specimen geometries. It was observed that the smaller the test specimen width, the higher the average tensile strength of the cellulose nanopapers. This can be described by the weakest link theory, whereby the probability of defects present in the cellulose nanopapers increases with increasing test specimen width. The Poisson's ratio and fracture resistance of CNF and BC nanopapers are also discussed.

  • Journal article
    Song W, Barber K, Lee KY, 2017,

    Heat-induced bubble expansion as a route to increase the porosity of foam-templated bio-based macroporous polymers

    , Polymer, Vol: 118, Pages: 97-106, ISSN: 0032-3861

    Macroporous polymers were prepared by mechanically frothing a bio-based epoxy resin and hardener mixture to first create air-in-resin liquid foams, followed by curing of these liquid foams. It was found that heating the air-in-resin liquid foams prior to their gelation decreased the viscosity of the resin mixture and increased the pressure of the air bubbles, leading to an isotropic expansion of the air bubbles. This resulted in an increase in the porosity of the resulting foam-templated macroporous polymers from 71% to 85%. Correspondingly, the compressive moduli (E) and strengths (σ) of the foam-templated macroporous polymers decreased from 231 MPa and 5.9 MPa, respectively, to 58 MPa and 1.9 MPa, respectively. This decrease is attributed to an increase in the porosity and pore throat frequency of the foam-templated macroporous polymers when heat was applied to the liquid foams. The deformation of the pores based on in situ SEM micro-compression test of the fabricated foam-templated macroporous polymers is also discussed.

  • Journal article
    Tagarielli V, song Y, li Y, song W, yee K, lee KYet al., 2017,

    Measurements of the mechanical response of unidirectional 3D-printed PLA

    , Materials & Design, Vol: 123, Pages: 154-164, ISSN: 0261-3069

    Fully dense PLA blocks were manufactured by 3D-printing, depositing a polymer filament in a single direction via the fusion deposition method (FDM). Specimens were cut from printed blocks using conventional machining and were used to perform tension, compression and fracture experiments along different material directions. The elasto-plastic material response was found to be orthotropic and characterised by a strong tension-compression asymmetry; the material was tougher when loaded in the extrusion direction than in the transverse direction. The response of the unidirectional, 3D-printed material was compared to that of homogeneous injection-moulded PLA, showing that manufacturing by 3D-printing improves toughness; the effects of an annealing thermal cycle on the molecular structure and the mechanical response of the material were assessed.

  • Journal article
    Fortea-Verdejo M, Bumbaris E, Burgstaller C, Bismarck A, Lee Ket al., 2017,

    Plant fibre reinforced polymers: where do we stand in terms of tensile properties?

    , International Materials Reviews, Vol: 62, Pages: 441-464, ISSN: 1743-2804

    Plant fibres have a unique set of properties ranging from being stiff and brittle, such as hemp and flax, to more ductile, such as coir, combining these properties with their cost and availability makes them attractive alternative reinforcements for the production of greener composites. This article reviews the tensileproperties ofvarious plant fibreor plant based natural fibre-reinforced polymersreported in the literature. We critically discuss the use of plant fibres as reinforcement for the production of bio-based,renewable or green polymer composites, showing the evolution of the properties of plant fibre composites. The reported tensile properties of plant fibre-reinforced polymer composites arecompared against various renewable and non-renewableengineering/commoditypolymers as well as the tensile propertiesof commercially available randomly oriented glass fibre-reinforced polymers (GFRP). Green composites containing random short plant fibres dohave similar properties to randomly oriented GFRP at a lower overall part weight. Unidirectional plant fibre-reinforced polymers offer better performance than randomly oriented GFRP and could have the potential to be adapted in applications requiring even higher mechanical performance, especially in areas where the useof costly synthetic fibres might be less attractive. Furthermore, plant fibres can also be regarded as effective fillers to replace more expensive polymersand improve the green credentialsof final composite parts. These features may motivate the industry to introduce more plant fibre-based products to the market.

  • Journal article
    Shamsuddin SR, Lee KY, Bismarck A, 2016,

    Ductile unidirectional continuous rayon fibre-reinforced hierarchical composites

    , Composites Part A: Applied Science and Manufacturing, Vol: 90, Pages: 633-641, ISSN: 1359-835X

    Endless rayon fibres (Cordenka®) were used to reinforce polyhydroxybutyrate (PHB) nanocomposites containing 2.5 wt.% nanofibrillated cellulose (NFC) to create truly green hierarchical composites. Unidirectional (UD) composites with 50–55% fibre volume fraction were produced using a solvent-free continuous wet powder impregnation method. The composites exhibit ductile failure behaviour with a strain-to-failure of more than 10% albeit using a very brittle matrix. Improvements at a model composite level were translated into higher mechanical properties of UD hierarchical composites. The Young’s moduli of rayon fibre-reinforced (NFC-reinforced) PHB composites were about 15 GPa. The tensile and flexural strength of hierarchical PHB composites increased by 15% and 33% as compared to the rayon fibre-reinforced neat PHB composites. This suggests that incorporation of NFC into the PHB matrix binds the rayon fibres, which does affect the load transfer between the constituents resulting in composites with better mechanical properties.

  • Journal article
    Ferguson A, Khan U, Walsh M, Lee KY, Bismarck A, Shaffer MS, Coleman JN, Bergin SDet al., 2016,

    Understanding the dispersion and assembly of bacterial cellulose in organic solvents

    , Biomacromolecules, Vol: 17, Pages: 1845-1853, ISSN: 1526-4602

    The constituent nanofibrils of bacterial cellulose are of interest to many researchers because of their purity and excellent mechanical properties. Mechanisms to disrupt the network structure of bacterial cellulose (BC) to isolate bacterial cellulose nanofibrils (BCN) are limited. This work focuses on liquid-phase dispersions of BCN in a range of organic solvents. It builds on work to disperse similarly intractable nanomaterials, such as single-walled carbon nanotubes, where optimum dispersion is seen for solvents whose surface energies are close to the surface energy of the nanomaterial; bacterial cellulose is shown to disperse in a similar fashion. Inverse gas chromatography was used to determine the surface energy of bacterial cellulose, under relevant conditions, by quantifying the surface heterogeneity of the material as a function of coverage. Films of pure BCN were prepared from dispersions in a range of solvents; the extent of BCN exfoliation is shown to have a strong effect on the mechanical properties of BC films and to fit models based on the volumetric density of nanofibril junctions. Such control offers new routes to producing robust cellulose films of bacterial cellulose nanofibrils.

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