Surface modification of abaca fiber via radiation-induced graft polymerization for reinforcement of polymer composites

Abaca fibers are known for being one of the strongest fibers in the world and are widely utilized in polymer composites because of their excellent mechanical properties, low density, renewability and low cost. Factors limiting their maximum potential are their inherent hydrophilicity and poor compatibility with polymeric matrices, both of which affects fiber-matrix interaction. Fiber-matrix interaction at the interphase is one very important property in the area of polymer composites that facilitates stress transfer between resin and filler. Here, we present an approach to address this problem through radiation-induced graft polymerization (RIGP). RIGP is a simple, environment-friendly method of surface modification for natural fibers which can introduce compatible groups on the fiber surface without damaging its bulk properties. Glycidyl methacrylate was successfully grafted on the surface of abaca woven fabric by RAFT-mediated RIGP in emulsion. The degree of grafting and molecular weights were varied using different absorbed doses, monomer concentrations and RAFTto-monomer ratios. Grafting was verified by FTIR, SEM, XPS and TGA. Molecular weight analysis using GPC and NMR showed linear increase in the molecular weights with the monomer conversion. There is a good agreement of the measured molecular weights and the theoretical values, while also achieving narrow polydispersity in the grafted polymers. PGMA-grafted abaca fibers showed increased tensile strength, thermal stability and moisture resistance over unmodified fibers. Using the grafted abaca as composite reinforcement material showed improvement in tensile and flexural strength of at least 23 and 59% compared to untreated fibers. The highest improvement was noted for fabrics grafted using RAFT mechanism owing to its uniform coverage which elicits a better compatibilization effect. Shorter grafts were also observed to produce the greatest improvement in mechanical strength, thermal stability and moisture resistance owing to higher graft density which translated to better interfacial adhesion. Further functionalization of the PGMA-grafted abaca fibers in order to introduce covalent linkages between the fiber and the resin was successfully carried out using 1- vinylimidazole. However, the derivatization process ended up making the fiber brittle and resulted in lower tensile strength and thermal stability than its grafted counterpart. This decrease in fiber integrity also affected resulting composites. The results of composite testing showcase the potential of the technique as a surface modification tool for the enhanced utilization of natural fibers in the composite industry

Simple fabrication of gelatin-polyvinyl alcohol bilayer hydrogel with wound dressing and nonadhesive duality

腹部外科手術後における臓器間の癒着は最も一般的で重篤な合併症の一つである。様々なバリア材料が開発されているものの、創傷治癒と癒着防止の両立は困難であった。そこで本研究では、1回のガンマ線照射で細胞接着性が高いゼラチンと細胞接着性の低いポリビニルアルコール（PVA）を架橋・ゲル化させると共に、２層を化学的に結合する技術を開発した。作製した2層ゲルの有効性は、物理化学的な特性に加え、生分解性試験や細胞培養試験で評価した。傷害部位に接するゼラチン側には細部が良好に接着し、組織再生や治癒が促進される。一方、周囲組織に接するPVA側では細胞や組織が癒着しない。そのため、開発した２層ゲルは術後の回復を促進する理想的なバリア材料として、医療分野で役立つことが期待される

Radiation-Induced Controlled Grafting from Lignocellulosic Fiber Towards Compatibilization for Composite Reinforcement

Lignocellulosic natural fibers remain at the forefront of eco-friendly and sustainable reinforcement materials in composites. This work addresses the inherent limitations of lignocellulosic fibers in terms of their hydrophilicity and incompatibility to achieve maximum utilization in most commercial resins using a reversible addition-fragmentation chain transfer radiation-induced graft polymerization (RAFT-RIGP) approach. The one-pot surface modification technique via RAFT-RIGP was shown to efficiently graft poly(glycidyl methacrylate) onto lignocellulosic fibers like abaca. Results from the analyses of the different grafting parameters and polymerization trends reveal that the employed RAFT-mediation improved grafting yield compared to a conventional RIGP despite retardation effects inherent in the RAFT mechanism. Additionally, sufficient control over the molecular weight and dispersity of grafted chains was exhibited. The modified fibers showed improved tensile strength, higher thermal stability and reduced moisture uptake. Overall, we have demonstrated that RAFT-RIGP can be a facile, environment-friendly technique for the surface compatibilization of lignocellulose fibers without the mechanical deterioration of substrate properties, unlike other fiber modification processes. Therefore, this method has a great potential in natural fiber compatibilization for reinforcement in polymer composites

Properties and Potential Applications of Carboxymethyl-kappa-carrageenan Hydrogels Crosslinked by Gamma Radiation

Carboxymethyl derivatives of k-carrageenan(CMkC), with different degrees of substitution, were gamma-irradiated in viscous or paste solutions. Successfully obtained chemically crosslinked hydrogels showed dependence on the degree of substitution(DS), concentration, and radiation dose. The highest gel fraction was 76% exhibited by CMkC-3s hydrogel with a DS of 1.58. The hydrogels showed different swelling degrees in water and saline. Swelling behavior versus time, in both solvents, corresponded to 2nd order kinetics. The CMkC-3s at 20% concentration irradiated at 15 kGy had the highest water absorption of 324 g water/g dry gel. Selected hydrogels were evaluated for applications as wound dressing, as water retainer in sandy soil, and as metal adsorbent. As a wound dressing, CMkC-2s and CMkC-3s hydrogels exhibited considerable tensile strengths, abilities to absorb pseudo extracellular fluid and extractables with pH/conductivity conducive for healing promotion. In addition, the CMkC-3s hydrogel had no cytotoxic potential based on the MTT test. As water retainer in sandy soil, test samples with 0.1, 0.3 and 0.5% CMkC-3s granules retained 25.1%, 32.2%, and 42.6% water, respectively, at day 0 compared to 19.2% of the sandy soil alone. On day 7, the three sandy soil-CMkC groups still had 13.7%, 19.4%, and 29.3% water while the control had only 3.85%. In the batch adsorption studies, the hydrogels adsorbed heavy metals (Cu2+, Zn2+, Cd2+ and Pb2+) in the solution at different capacities, with Cd2+ as the highly adsorbed and Pb2+ as the least. The CMkC-3s hydrogel showed the highest metal uptake and adsorption efficiency, followed by CMkC-2s, then CMkC-1s. The CMkC-3s hydrogel, further tested on pH effect, had optimum metal uptake at neutral pH

RAFT-Mediated Radiation Grafting on Natural Fibers in Aqueous Emulsion

Using aqueous emulsion as the medium in radiation-induced graft polymerization (RIGP) offers an environment-friendly shift from organic solvents while increasing polymerization efficiency through known water radiolysis-based graft initiation. In the present paper, we further extend the applicability of RIGP in emulsion under the influence of reversible addition fragmentation chain transfer (RAFT) mechanisms. Emulsions prepared with Tween 20 showed good colloidal stability for several hours. Subjecting it to simultaneous irradiation with abaca fibers resulted in successful grafting, supported by gravimetric, IR, SEM, and TG analysis. A correlation was drawn between smaller monomer micelles and the enhancement of grafting driven by diffusion and surface area coverage. RAFT mechanisms were also conserved based on molecular weight evolution. RAFT-mediated RIGP in aqueous emulsion shows good potential as a versatile and green surface modification technique for natural fibers for various functional applications

Nanografting of Polymer Brushes on Gold Substrate by RAFT-RIGP

Optical sensors based on surface plasmon resonance (SPR) have made great strides in the detection of various chemical and biological analytes. A surface plasmon is a bound, non-radiative evanescent wave generated as resonant electrons on a metal–dielectric surface to absorb energy from an incident light. As analytes bind to a functionalized metal substrate, the refractometric response generated can be used for quantitation with great selectivity, sensitivity, and capacity for label-free real-time analysis. Polymer nanobrushes are ideal recognition elements because of their greater surface area and their wide range of functional versatility. Here, we introduce a simple “grafting-from” method to covalently attach nanometer-thick polymer chains on a gold surface. Nanografting on gold-coated BK-7 glass was performed in two steps: (1) self-assembly of organosulfur compounds; and (2) RAFT-mediated radiation-induced graft polymerization (RAFT-RIGP) of polyglycidyl methacrylate (PGMA). Surface modification was monitored and verified using FTIR and SPR. Layer-by-layer thickness calculated based on Winspall 3.02 simulation fitted with experimental SPR curves showed successful self-assembly of 1-dodecanethiol (DDT) monolayer with thickness measuring 1.4 nm. These alkane chains of DDT served as the graft initiation sites for RAFT-RIGP. Nanografting was controlled by adjusting the absorbed dose in the presence of chain transfer agent, 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid. The molecular weight of grafted polymers measuring 2.8 and 4.3 kDa corresponded to a thickness increase of 3.6 and 7.9 nm, respectively. These stable nanografted gold substrates may be further functionalized for sensing applications