Fabrication and characterization of wheat gliadin hydrogels with high strength and toughness

Fabricating a hydrogel with high strength and toughness is still a challenge in many fields. Here, we prepared gliadin-based hydrogels by chemical cross-linking gliadin in acetic acid solution (GS) with glutaraldehyde (GA). Subsequently, the overall properties of the fabricated hydrogels were systematically investigated in terms of their mechanical properties, swelling ratio, weight loss, thermal stability, and the chemical/physical interactions in hydrogels. Results showed that the gliadin-based chemically cross-linked hydrogels exhibited excellent mechanical properties. The optimized hydrogel exhibited the compressive stress of 1.8 MPa at a strain of 70%, and an excellent self-recovery property after 30 cycles of loading-unloading treatments. The strength and toughness of the hydrogels could be tailored by adjusting the ratio of GS/GA. The chemical cross-linking (aldehyde-ammonia reaction) was the main molecular interaction in the hydrogels, including single-/multi-site crosslinking, and the hydrogen bond was the only physical cross-linking in the hydrogels. Moreover, the swelling ratio of the fabricated hydrogels performed a concentration negative-dependency in GA or GS concentration. And a higher GS concentration (40%) with an appropriate GA content (3.0%) could resist the degradation of hydrogels. In addition, the thermodynamic properties of hydrogels also improved by the GA addition. Overall, these findings suggested that gliadin can be applied for fabricating hydrogels with tunable mechanical properties, which will unlock the high-utilization of gliadin as biopolymer and biocompatible materials.     

Thermal,swelling and stability kinetics of chitosan based semi-interpenetrating network hydrogels

The present study is focused on studying the swelling kinetics, thermal and aqueous stabilities, and determination of various forms of water in the chitosan (CS) and polyacrylonitrile (PAN) blend and semi-interpenetrating polymer network (sIPN). CS/PAN blend hydrogel films were prepared by solution casting technique. The blend film with optimum swelling properties was selected for the synthesis of sIPN. CS in the blend was crosslinked with the vapors of Glutaraldehyde (GTA) to prepare sIPN. The fabricated CS/PAN blend and sIPN hydrogels films were characterized with Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA) and field emission scanning electron microscope (FESEM). The kinetics of swelling, bound and unbound waters and aqueous stability were determined experimentally. FESEM showed good miscibility between CS and PAN, FTIR showed no chemical interaction between CS and PAN; however, it did show a doublet for the sIPN, TGA showed improved thermal stability and swelling kinetic followed second order kinetics. The degree of swelling of the sIPN hydrogels samples at room temperature varied from ~2200 % (with a fair degree of stability (~30 %)) to ~1000 % (with high degree of aqueous stability (43 %)) with increase in the crosslinking time. The calculated unbound water (W_UB) max., for the blend was 52.3 % whereas for the bound (W_B) the max., was 41.9 %. However, for sIPN hydrogel films, the W_UB water decreased (max. 21.0 %) where as the W_B increased (max. 52.0 %). The decrease in W_UB and increase in the W_B is attributed to the formation of a compact structure and increase in the contact area between the water and polymers in sIPN hydrogels due to the induction of new water contacting point in these hydrogel films, respectively.     

High water content silk protein-based hydrogels with tunable elasticity fabricated via a Ru(II) mediated photochemical cross-linking method

Silk is very promising in the field of biomaterials as a natural biomacromolecule. Silk protein can be made into various forms of materials, including hydrogels. However, silk protein-based hydrogels have not attracted much attention due to its weak mechanical properties. Here, we report high water content silk protein-based hydrogels with tunable elasticity which were fabricated through Ru(II) mediated photochemically cross-linking tyrosine residues in regenerated silk protein. The regenerated silk protein was characterized by Fourier transform infrared spectroscopy (FTIR). The gelation kinetics of the silk protein was studied by rheology measurements. The compressive mechanical properties of the silk protein-based hydrogels was investigated using compressive tests and dynamic mechanical analysis (DMA). Compressive modulus of the hydrogels reached 349±64 MPa at 15 % strain. The fabricated silk protein-based hydrogels were also characterized by Scanning electron microscopy (SEM), revealing an interconnected porous network structure, typical of hydrogels, with an average pore size of approximately 130 μm. Finally, biocompatibility of the silk protein-based hydrogels was demonstrated through cell culture studies using a human fibroblast cell line, HFL1. The reported silk protein-based hydrogels represent a promising candidate for biomaterial applications.     

Investigation of a-PVA/s-PVA hydrogels prepared by freezing-thawing method

The hydrogels of atactic poly (vinyl alcohol) (a-PVA) and syndiotactic poly (vinyl alcohol) (s-PVA) with different blend ratios were prepared by freezing-thawing processes. The effect of s-PVA on gelation behavior of the blend was investigated in terms of gelation temperature (T _gel) and hydrogel melting temperature (T _gm). And swelling behavior, crystallization, thermal properties, morphology of the blend hydrogels were also studied. With the increase of s-PVA, T _gel of the blend solution and T _gm of the blend hydrogels increase. Both crystallinity and crystallite dimensions based on the XRD profiles are nearly monotonically increasing functions of s-PVA content. FTIR results indicate the number of hydrogen bonds raises with s-PVA increasing. DSC results demonstrate s-PVA favors improvement of hydrogels thermal stability. According to SEM images of hydrogels, the increase of cross-linking caused by s-PVA in the blend hydrogels results in denser structure, which in turn leads to increased gel fraction (G) and Hardness. 50/50 (a-PVA/s-PVA) blend hydrogel has a denser structure with EWC of 73.6 %, hardness of 22.8 HA and T _m of 236.15 °C. The result indicates blending a-PVA and s-PVA is a useful method to form the hydrogel having good thermal stability and relative high degree of swelling.     

Optimum heat treatment conditions for PAN-based oxidized electrospun nonwovens

In this study, the polyacrylonitrile (PAN)-based precursor was produced by electrospinning for the fabrication of oxidized nanofiber nonwovens. The parameters adopted for the oxidation process were chosen from the thermal analysis results obtained using DSC and TGA. The oxidation temperatures of 270, 300, and 330 oC were selected for heating times of 30, 50, and 70 min at three levels of tension. The variations in yield rate, breaking strength, shrinkage and stiffness of the oxidized PAN-based electrospun nonwovens were examined in this article. The results indicate that the physical properties of electrospun nonwovens were affected by the oxidation conditions. In addition, the limit oxygen index (LOI) was found to increase with increasing heat treatment temperature and time. In addition, the optimum oxidation condition was found to be heating temperature of 300 °C for a duration of 70 min. Under this condition, high-quality PAN-based oxidized electrospun nonwovens were produced with aromatization index (AI) of 62 % and LOI of 44 %.     

Influence of natural clinoptilolite nanoparticles on thermal stability,scratch resistance and adherence properties of Acrylonitrile butadiene styrene (ABS)

In order to improve thermal stability of Acrylonitrile-butadiene-styrene (ABS) polymer, ABS/natural clinoptilolite (Clino) nanocomposite was produced using solvent/non-solvent method. The influence of natural clinoptilolite nanoparticles on scratch resistance and adherence properties of ABS coating on steel coupons was investigated. In order to study the scratch resistance and adherence properties, thin (20 µm) coatings of ABS and ABS/Clino nanocomposites, were prepared by solution casting method. The formation of ABS/Clino nanocomposite was characterized using FTIR spectroscopy, X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM). Results showed that there is a strong interaction such as hydrogen bonding between ABS and clinoptilolite nanoparticles. The thermal stability of the nanocomposite was examined using thermogravimetric analysis (TGA). TGA results showed an increase in the thermal degradation temperature of the nanocomposite. TGA results indicated that the thermal stability of ABS increases by increasing the Clino content of nanocomposite up to 5 % w/w. Scratch resistance and adherence properties of ABS/Clino nanocomposite coatings were also evaluated. Results showed that the scratch resistance and adherence strength of ABS/Clino nanocomposite coatings are higher than that of pure ABS coatings.     

Some of the mechanical and thermal properties of wheat straw filled-PP composites

The objective of this investigation was to evaluate the mechanical, thermal stability and viscoelastic behaviors of experimental PP composites made from wheat straw and PP-g-MA coupling agent. Four levels of wheat straw, 10, 20, 25 and 30 wt % and two levels of coupling agent, 0 and 3 % wt were mixed with PP in rotary type mixer and injection molding process, respectively. Tensile characteristics and impact strength, thermal gravity and dynamic mechanical and thermal analysis of the samples were evaluated. Based on the results, it was observed that the tensile properties increased and impact strength decreased with the increase in the fiber loading from 10 % to 30 %. Further, the composites treated with PP-g-MA exhibited improved mechanical properties which confirmed efficient fiber-matrix adhesion. DMT analysis showed that the PP composites made of 30 % wheat straw containing 3 % PP-g-MA showed the highest E’ and lowest tan δ than the untreated ones. Also, the thermal stability of wheat straw was lower than PP and as filler content in the composites increased, the thermal stability decreased and the ash content increased.     

Mechanical behavior of composites reinforced with fibers caroa

Composites were prepared with 13, 23 30 and 40 % fiber and evaluated the mechanical performance in tensile, flexural and impact. The mechanical properties of these composites were also evaluated function of time at 110 °C thermal exposure. Caroa fibers were characterized by techniques such as thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the best mechanical properties were achieved for composites containing 23 to 30 % fiber. The incorporation of 23 % fiber caroa increased both the modulus of elasticity in the tensile test as the flexural strength and impact, the composite with 30 % fiber caroa showed higher tensile strength. The results show that the tensile and flexural strength of the composite decreased with time of thermal exposure. The thermal aging at 110 °C caused a decrease in tensile properties of the composites.     

Electrospinning of <Emphasis Type="Italic">Bombyx mori</Emphasis> silk fibroin nanofiber mats reinforced by cellulose nanowhiskers

Cellulose nanowhisker (CNW) reinforced electrospun Bombyx mori silk fibroin (SF) nanofibers were fabricated. The morphology, structure, and mechanical properties of nanofibers were investigated by FE-SEM, TEM, FTIR, and tensile testing. It was found that the nanofiber size decreased obviously from 250 nm in the unreinforced mat to 77–160 nm in the CNW reinforced mats depending on the CNW content due to the increased conductivity of spinning dope. In the reinforced mats, the CNWs were embedded in the SF matrix separated from each other, and aligned along the fiber axis. There was a positive correlation between the CNW content and the tensile strength and Young’s modulus of reinforced mats. However the strain at break dropped gradually with the increase of CNW. When the CNW content was 2 w/w%, the tensile strength and Young’s modulus of reinforced SF nanofiber mats were about 2 times higher than those of unreinforced mat.     

Preparation process and antimicrobial properties of cross-linking chitosan onto periodate-oxidized bamboo pulp fabric

Chitosan cross-linked bamboo pulp fabric (CCBPF) was prepared by treating the oxidized bamboo pulp fabric with the chitosan aqueous acetic acid solution. FTIR spectroscopy was used to examine the chemical bonding between chitosan and oxidized bamboo pulp fabrics, X-ray diffraction and thermogravimetry were used to detect the cellulose structure. The impact of the periodate oxidation and chitosan treatment on the physical properties of bamboo pulp fabrics was evaluated by determining the aldehyde content, weight loss, mechanical strength, wrinkle recovery angle, and moisture regain of fabrics as well as chitosan content in the composite chitosan-bamboo pulp fabrics. Antibacterial activity of the CCBPF against Staphylococcus aureus and Escherichia coli was investigated in vitro experiments. The results indicated that the aldehyde groups in the periodate oxidized bamboo pulp cellulose were reacted with the amino groups of chitosan to form Schiff base, and the resultant CCBPF displayed good wrinkle recovery angle and moisture regain. In comparison with those of the oxidized bamboo pulp fabric, the CCBPF exhibited a lower thermal stability, the crystallinity decreased from 42.73 % to 39.15 %, the mechanical strength of CCBPF had no significant change, and the CCBPF showed excellent antibacterial activity against both types of bacteria which was durable till 50 washes.     

Preparation and characterization of fibers of waste and fresh polyethylene terephtalate and mixtures of them

Textile fibers were obtained from secondary polyethylene terephtalate (PET) and its mixtures with primary PET at initial orientation of 18000–33000 %, rate of additional orientation drawing 3.5–6.5 times and temperature of thermal fixation 363–413 K. The fibers’ tensile strength was found to decrease and elongation at break to increase with the decrease of their linear density under the conditions of fibers formation. For the fibers based on polymer mixtures, the presence of oxidized fragments in the secondary PET limited the compatibility of the two polymers which resulted in deteriorated tensile properties. The linear density (4–16 dtex), tensile strength (30–50 cN/tex) and elongation at break (20–60 %) of the PET fibers obtained were close to these for the industrially produced polymer fibers. The values of the average diameter of the fibers formed and oriented under laboratory conditions allows classifying them between the fine and the coarse textile fibers which makes them suitable for the textile industry.     

Effect of mercerization on mechanical, thermal and degradation characteristics of jute fabric-reinforced polypropylene composites

Jute fabric reinforced polypropylene composites were fabricated by compression molding technique. Fiber content in the composites was optimized at 45 % by weight of fiber by evaluating the mechanical parameters such as tensile strength, tensile modulus, bending strength, bending modulus. Surface treatment of jute fabrics was carried out by mercerizing jute fabrics with aqueous solutions of NaOH (5, 10 and 20 %) at different soaking times (30, 60 and 90 mins) and temperatures (0, 30 and 70 °C). The effect of mercerization on weight and dimension of jute fabrics was studied. Mechanical properties of mercerized jute-PP composites were measured and found highest at 20 % NaOH at 0 °C for 60 min soaking time. Thermal analytical data from thermogravimetric and differential thermal analysis showed that mercerized jute-PP composite achieved higher thermal stability compared to PP, jute fabrics and control composite. Degradation characteristics of the composites were studied in soil, water and simulated weathering conditions. Water uptake of the composites was also investigated.     

Effect of coir fiber content and compatibilizer on the properties of unidirectional coir fiber/polypropylene composites

The main objective of this research was to study the effect of fiber content variation and stearic acid (SA) treatment on the fundamental properties of unidirectional coir fiber (CF) reinforced polypropylene (PP) composites. Several percentages of filler contents were used (10–40 wt %) in order to gain insights into the effect of filler content on the properties of the composites. Coir/PP composites were fabricated by compression molding, and the properties of composites were studied by physico-mechanical and thermal properties. The results from mechanical properties such as tensile strength (TS), tensile modulus (TM) and impact strength (IS) of the CF/PP composites were found to be increased with increasing fiber content, reached an optimum and thereafter decreased with further increase in fiber content. Treatment of the coir with SA as the coupling agent enhanced the mechanical properties, crystallization temperature and crystallinity of virgin PP and water desorption of the resulting composites, resulting from the improved adhesion between the CF and PP matrix. Scanning electron micrographs (SEM) of the tensile fractured samples showed improved adhesion between fiber and matrix upon treatment with SA. Interfacial shear strength (IFSS) of the composites was measured by single fiber fragmentation test (SFFT).     

Chitosan-filled polypropylene composites: The effect of filler loading and organosolv lignin on mechanical,morphological and thermal properties

In this work, the effect of organosolv lignin on properties of polypropylene (PP)/chitosan composites was investigated. Mechanical and thermal properties of the composites were analyzed by means of ASTM D 638-91, ASTM D 256, thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Tensile strength and elongation at break of the PP composites decreased upon the presence of chitosan filler, but Young’s modulus improved. Impact strength was found to increase with the maximum value at 30 php of filler loading. At a similar loading, treated PP/chitosan composites were found to have higher tensile strength, elongation at break, Young’s modulus as well as impact strength than untreated composites. Furthermore, the presence of organosolv lignin imparted a plasticizing effect. Thermal properties of the treated PP/chitosan composites were better as compared with the untreated PP/chitosan composites; although the chemical treatment did not alter the thermal degradation mechanism. In addition, the obtained results were comparable to results from previous studies. This finding implied that the organosolv lignin could be a potential reagent to replace its synthetic counterpart.     

Wheat gluten films cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide

Wheat gluten films were cast from aqueous dispersions containing 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as cross-linking reagents and glycerol as a plasticizer. Cross-linking was carried out to improve film properties such as water sensitivity and tensile strength. Films were characterized by measuring protein and water content, amount of amino groups, swelling of the films in water, and mechanical properties such as tensile strength (σ_max) and strain at maximum stress ( at σ_max). The use of different ratios of EDC to COOH resulted in different tensile properties and different percentage of swelling, which was attributed to the degree of cross-linking in the film. At a ratio of EDC/NHS/COOH=0.5/0.5/1, films had a water content of 10–11.5% and showed the highest σ_max (2.8±0.9 MPa), the lowest at σ_max (142±67%), and the lowest swelling (46%) compared to σ_max=1.7±0.4 MPa, at σ_max=257±63%, and swelling=68% for native gluten films.     

Nanocellulose reinforced PVA composite films: Effects of acid treatment and filler loading

Nanocellulose was prepared by acid hydrolysis of microcrystalline cellulose (MCC) at different hydrobromic acid (HBr) concentrations. Polyvinyl alcohol (PVA) composite films were prepared by the reinforcement of nanocellulose into a PVA matrix at different filler loading levels and subsequent film casting. Chemical characterization of nanocelluloses was performed for the analysis of crystallinity (X_c), degree of polymerization (DP), and molecular weight (M_w). The mechanical and thermal properties of the nanocellulose reinforced PVA films were also measured for tensile strength and thermogravimetric analysis (TGA). The acid hydrolysis decreased steadily the DP and M_w of MCC. The crystallinity of MCC with 1.5 M and 2.5 M HBr showed a significant increase due to the degradation of amorphous domains in cellulose. Higher crystalline cellulose showed the higher thermal stability than MCC. From X-ray diffraction (XRD) analysis, nanocellulose samples showed the higher peak intensity than MCC cases. Reduction of MCC particle by acid hydrolysis was clearly observed from scanning electron microscope (SEM) images. The tensile and thermal properties of PVA composite films were significantly improved with the increase of the nanocellulose loading.     

Preparation and properties of alkaline functionalized carbon nanotubes reinforced polyurethane composites

Composites consisting of polyurethane (PU)/carbon nanotubes (CNTs) have been successfully prepared by solution mixing method. CNTs were modified through mechano-chemical reaction to increase the compatibility with PU via hydrogen bondings. SEM microphotographs proved that modified CNTs (M-CNTs) became shorter and FTIR spectra showed that hydroxyl groups had been introduced to the surface of M-CNTs. SEM images of PU/M-CNTs composites also proved that M-CNTs were effectively dispersed in PU matrix. Mechanical property tests showed that addition of M-CNTs could significantly improve the tensile properties of PU/M-CNTs composite (breaking strength enhancement ratio for composite with 5.0 wt% M-CNTs was 103.81 %). The thermal stability of composites with M-CNTs was also improved. The initial degradation temperature enhancement was 19.9 oC for the composite with 0.5 wt% M-CNTs. Electrical property tests showed that the electrical properties were improved by adding M-CNTs. The volume conductivities increased 3 and 5 orders of magnitude for the composites with 5.0 wt% and 10 wt% M-CNTs, respectively. The addition of M-CNTs had little effect on the elastic properties of the composites.     

Facilitation of α-polylysine in TGase-mediated crosslinking modification for gluten and its effect on properties of gluten films

In this study, α-polylysine was used to enhance the cross-linking effect of TGase on gluten and its effects on properties of gluten films were investigated. The amount of free ammonia released from the cross-linking reaction of gluten induced by TGase at the presence of α-polylysine obviously increased, and more polymers with higher molecular weight were formed from the SDS-PAGE results, which indicated that the TGase-mediated cross-linking reaction ability of gluten was strengthened with the incorporation of α-polylysine. The tensile strength of the films from gluten modified with TGase (20 units/g wheat gluten) and 2% α-polylysine (g/g gluten) for 3 h increased from 4.02 ± 0.09 MPa to 5.28 ± 0.14 MPa, which was more effective than that treated with TGase alone (in which the tensile strength of the films was 4.49 ± 0.10 MPa). The TGase treatment with α-polylysine of gluten improved the water stability of the films much more than that treated with TGase alone. A rougher surface and a more compact cross-section structure were observed by SEM for the films from TGase-α-polylysine treated gluten. The contact angles between the gluten films surface and a water droplet increased because of TGase-mediated cross-linking modification.     

Studies on composite filaments from nanoclay reinforced polypropylene

The development of high tenacity, high modulus monofilaments from Polypropylene/Clay nanocomposite has been investigated. Pure sodium montmorillonite nanoclay was modified using hexadecyl trimethyl ammonium bromide (HTAB) via an ion exchange reaction. Pure and modified clay were characterized through X-ray diffraction, FTIR and TGA. The modified clay was melt blended with polypropylene (PP) in presence of a swelling agent. Composite filaments from PP/Clay nanocomposite were prepared at different weight percentages of nanoclay and the spinning and drawing conditions were optimized. The filaments were characterized for their mechanical, morphological and thermal properties. The composite PP filaments with modified clay showed improved tensile strength, modulus and reduced elongation at break. The composite filaments with unmodified clay did not show any improvement in tensile strength but the modulus improved. The sharp and narrow X-ray diffraction peaks of PP/nanoclay composite filaments indicate increase in crystallinity in presence of modified clay at small loadings (0.5%). The improved thermal stability was observed in filaments with modified as well as unmodified clays.     

Preparation of poly(vinyl alcohol)/silver-zeolite composite hydrogels by UV-irradiation

Poly(vinyl alcohol) (PVA)/Ag-zeolite nanocomposite hydrogels were prepared by UV irradiation using PVA solution mixed with Ag-zeolite nanoparticles. Physical properties and changes in morphology of the PVA/Ag-zeolite hydrogels were investigated. The PVA/Ag-zeolite hydrogels were prepared at a PVA concentration of 9 wt% with a UV irradiation distance of 15 cm, where gel fraction and swelling ratio were optimized. Hardness of the PVA/Ag-zeolite hydrogels decreased with increasing amounts of Ag-zeolite, reaching that of soft elastomer when the amount of Ag-zeolite was 5 % by weight. The PVA/Ag-zeolite hydrogels showed strong antimicrobial activities against Staphylococcus aureus and Klebsiella pneumoniae, inducing a reduction of bacteria of over 99.9 % at a Ag-zeolite content of 3 wt%.