Stress transfer in microfibrillated cellulose reinforced poly(vinyl alcohol) composites

Copyright © 2014 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Composites Part A: Applied Science and Manufacturing. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Composites Part A: Applied Science and Manufacturing Vol. 65 (2014), DOI: 10.1016/j.compositesa.2014.06.014Combined homogenisation and sonication treatments of micron-sized lyocell fibres were used to generate microfibrillated cellulose (MFC) with fibril diameters of ∼350 nm. No further reduction in fibril diameter was observed after 30 min treatment. Poly(vinyl alcohol) (PVA) composites reinforced with these fibrils were fabricated using solvent casting and physical and mechanical properties were investigated. The presence of MFC in PVA increased the thermal degradation of the polymer. An increase in both the tensile strength and modulus of the composites was observed for up to 3 wt.% of fibrils; beyond this point no significant increases were observed. An estimate of ∼39 GPa is made for the fibril modulus based on this increase. Stress-transfer between the polymer resin and the fibrils was investigated using Raman spectroscopy. Stress transfer in the composite is shown to be greater than that of a pure network of fibres, indicating a good fibre–matrix bond.Royal Thai Governmen

Aligned-porous-structured poly(vinyl alcohol) foams with cellulose nanocrystals

Abstract Poly(vinyl alcohol) (PVA) foams were prepared using a green lyophilization process without the use of foaming agents. PVA solutions with contents of CNCs (1–4 wt%) were prepared at two different freezing temperatures (−20 and −186 °C). With the addition of CNCs, moisture uptake of the CNC-PVA foams prepared at two freezing temperatures was lower than the neat PVA foams. With increasing CNC contents, no significant change of the moisture uptake could be observed for both types of the foams. Similar values of the moisture uptake could be found from both foams frozen at −20 and −186 °C. Scanning electron microscope measurements revealed the aligned-porous-structure of the foams frozen at −186 °C along with the ice growth direction while large and elongated pores were observed from the foams with the lower freezing temperature. These unique features of the foams prepared by a freeze-drying technique could be controlled by changing the freezing temperature, and these foams could be useful for specific applications such as tissue engineering scaffolds, thermal insulators or filters

Cross-linked nanocomposite hydrogels based on cellulose nanocrystals and PVA:mechanical properties and creep recovery

Abstract Cellulose nanocrystal (CNC) reinforced poly(vinyl alcohol) (PVA) hydrogels with a water content of ∼92% were successfully prepared with glutaraldehyde (GA) as a cross-linker. The effects of the CNC content on the thermal stability, swelling ratio and mechanical and viscoelastic properties of the cross-linked hydrogels were investigated. The compressive strength at 60% strain for the hydrogels with 1 wt% CNCs increased by 303%, from 17.5 kPa to 53 kPa. The creep results showed that the addition of CNCs decreased the creep elasticity due to molecular chain restriction. The almost complete strain recovery (∼97%) after fixed load removal for 15 min was observed from the hydrogels with CNCs, compared with 92% strain recovery of the neat cross-linked PVA hydrogels. The incorporation of CNCs did not affect the swelling ratio and thermal stability of the hydrogels. These results suggest the cross-linked CNC-PVA hydrogels have potential for use in biomedical and tissue engineering applications

Preparation of Chitin Nanofibers from Shrimp Shell Waste by Partial Deacetylation and Mechanical Treatment

Chitin is one of the most abundant biopolymers in nature. Herein, we report the successful preparation of chitin nanofibers (ChNFs) from shrimp shell waste using a partial deacetylation process with NaOH and high-speed blending. The effects of the deacetylation reaction with NaOH concentrations (0–40 wt%) on the degree of acetylation (DA), crystallinity, zeta potential, thermal stability, and morphology of the ChNFs were investigated. With the more aggressive deacetylation reaction (higher NaOH concentration), ChNFs had the lower DA, crystallinity degree, and thermal stability, and their widths and lengths became smaller and shorter. The presence of amino groups in the chitin molecule caused by deacetylation generated repulsive forces with aids of acetic acid, efficiently leading to the individualization of ChNFs using high-speed blending. The individualized ChNFs deacetylated with 30 wt% NaOH had an average width of 8.07 ± 1.80 nm and length of less than 500 nm, whereas bundles of aggregated fibers with widths in the range of 30–100 nm and lengths of up to several μm were extracted from chitin without deacetylation. Additionally, the deacetylation with 40 wt% NaOH completely converted chitin to chitosan. The ChNFs could be efficiently used for composites, biomaterials, and packaging applications

Transparency, moisture barrier property, and performance of the alternative solar cell encapsulants based on PU/PVDC blend reinforced with different types of cellulose nanocrystals

Abstract Two different types of cellulose nanocrystals, derived from water hyacinth fibers and microfibrillated cellulose (MFC), were prepared using an acid hydrolysis treatment. These cellulose nanocrystals (CNCs) were further used as barrier enhancing fillers for polyurethane (PU) blended with 25 wt% of poly(vinylidene dichloride) (PVDC). The aim of this study was to investigate the effects of types and concentration of CNCs on mechanical, optical and barrier properties of polymer composite films. The feasibility of applying the obtained composite films as an encapsulating material for enhancing the lifetime of dye sensitized solar cells (DSSC) was also of interest. The acid hydrolysis of the MFC-yielded rod-shaped cellulose nanocrystals (CNCm) while the acid-hydrolyzed water hyacinth led to a formation of spherical-shaped cellulose nanocrystals (CNCw). Regardless of the types of CNCs, the optical transparency of the composite films was maintained well above 60%. According to results in this study, the most efficient film with the lowest water vapor transmission rate of 0.0517 g m−2 day−1 was the PU/PVDC film reinforced with 0.1 wt% of CNCm. The encapsulants made from this composite could prolong the lifetime of the DSSC devices for up to 14 days, with the normalized PCE value of 0.78. Overall, this work showed that the considerations of the barrier properties of the polymer encapsulants alone are insufficient to ensure that the system would be effective. An interfacial adhesion between the encapsulants and the electrodes, as well as some side reactions between polymers and chemicals inside the fabricated cell, should also be taken into account

Enhancement of the mechanical properties and water barrier properties of thermoplastic starch nanocomposite films by chitin nanofibers: Biodegradable coating for extending banana shelf life

Starch-based films have limited applications due to their hydrophilicity and poor mechanical performance. Herein, thermoplastic starch (TPS) nanocomposite films with chitin nanofibers (ChNFs) extracted from shrimp-shell waste were successfully fabricated using a solvent casting method. We investigated the effects of the ChNF loadings on the physical, mechanical, and water vapor barrier properties of the nanocomposite films. The well-dispersed ChNFs within the soft matrix associated with the formation of interfacial bonding between ChNFs and starch facilitated the efficient stress transfer from the soft matrix to the stiff ChNFs. Additionally, the presence of ChNFs created tortuous pathways within the films, which could impede the diffusion of water molecules. This resulted in a significant improvement in the mechanical properties, wettability, water resistance, and water vapor barrier properties of the nanocomposites. Compared to the results obtained from the neat TPS films, the TPS nanocomposites reinforced with ChNFs exhibited a 300% higher tensile stress, a 603% Young's modulus, and a considerable increase in the water contact angle, shifting from 86.2° to 98.6°. Furthermore, the ChNF-reinforced nanocomposite films showed no fragmentation after being soaked in water for 12 h under vigorous stirring, whereas the neat TPS films disintegrated under the same conditions. Interestingly, we found that coating a suspension of TPS and ChNFs on bananas effectively delayed their aging, preventing the color change from green to yellow. This promising result demonstrates the potential of the developed coating to extend the shelf life of fresh food produce, reducing food waste and the reliance on single-use petroleum-based packaging

Microfibrillated cellulose reinforced poly(vinyl alcohol) composites

Microfibrillated cellulose (MFC) was successfully prepared from lyocell fibers using combined homogenization and sonication treatments. MFC fibrils with a mean diameter of ~365 nm were observed, after the lyocell fibers with diameters of ~10 μm were mechanically treated for 60 min. Poly (vinyl alcohol) (PVA) composites reinforced with MFC were then fabricated using a solvent casting method. Physical and mechanical properties of the MFC reinforced PVA composites were investigated. An increase of ~13 and ~34 % of tensile strength and Youngs modulus was observed for the 3 wt% MFC reinforced composites, compared to those of the pure PVA. Raman spectroscopy was also employed to study the deformation micromechanics of the MFC reinforced PVA composites. The position of the Raman peak initially located at 1095 cm-1, corresponding to the C-O ring stretching and C-O-C glycosidic bond stretching modes, was recorded. During tensile deformation, this peak was observed to shift towards a lower wavenumber position, indicating stress-transfer between the resin and the fibrils.</jats:p

Development of chitin nanofiber coatings for prolonging shelf life and inhibiting bacterial growth on fresh cucumbers

Abstract The widespread usage of petroleum-based polymers as single-use packaging has had harmful effects on the environment. Herein, we developed sustainable chitin nanofiber (ChNF) coatings that prolong the shelf life of fresh cucumbers and delay the growth of pathogenic bacteria on their surfaces. ChNFs with varying degrees of acetylation were successfully prepared via deacetylation using NaOH with treatment times of 0–480 min and defibrillated using mechanical blending. With longer deacetylation reaction times, more acetamido groups (–NHCOCH3) in chitin molecules were converted to amino groups (–NH2), which imparted antibacterial properties to the ChNFs. The ChNF morphologies were affected by deacetylation reaction time. ChNFs deacetylated for 240 min had an average width of 9.0 nm and lengths of up to several μm, whereas rod-like structured ChNFs with a mean width of 7.3 nm and an average length of 222.3 nm were obtained with the reaction time of 480 min. Furthermore, we demonstrated a standalone ChNF coating to extend the shelf life of cucumbers. In comparison to the rod-like structured ChNFs, the 120 and 240-min deacetylated ChNFs exhibited a fibril-like structure, which considerably retarded the moisture loss of cucumbers and the growth rate of bacteria on their outer surfaces during storage. Cucumbers coated with these 120 and 240-min deacetylated ChNFs demonstrated a lower weight loss rate of ⁓ 3.9% day−1 compared to the uncoated cucumbers, which exhibited a weight loss rate of 4.6% day−1. This protective effect provided by these renewable ChNFs holds promising potential to reduce food waste and the use of petroleum-based packaging materials