Preparation of multiple-reactive-site and flexible crosslinking agent with transaconitic acid and acrylic acid and its application for three-dimensional crosslinking of cellulose

A novel multiple-reactive-site crosslinking agent, P(TAA‒AA), was developed from transaconitic acid and acrylic acid in this study. Cotton fabrics with durable wrinkle-resistant properties were obtained by crosslinking with P(TAA‒AA), which benefited from the multifunctional carboxyl groups of crosslinking agents and the three-dimensional crosslinking inside cotton fibers. The wrinkle-resistant properties of P(TAA‒AA)-modified fabrics were evaluated and compared with those of other polycarboxylic acid-treated fabrics, and the P(TAA‒AA)-modified fabrics showed a wrinkle recovery angle of 262° as high as the 1,2,3,4-butanetetracarboxylic acid-modified fabrics while maintaining nearly two-fold higher tearing strength retention (62.9%), and they showed a much higher value of whiteness index than the citric acid-modified fabrics. This demonstrated that the obtained P(TAA‒AA) is an ideal polycarboxylic acid already known to date simultaneously to realize the high wrinkle recovery angle and high tearing strength retention for treated cotton fabrics. The Raman depth mapping images and the scanning electron microscope images of P(TAA‒AA)-modified samples indicated that P(TAA‒AA) molecules can diffuse into the amorphous regions of the cellulose fibers and form crosslinking bridges between cellulose chains. The multiple reactive carboxyl groups in P(TAA‒AA) may form three or more ester bonds between the P(TAA‒AA) molecule and different cellulose chains, which were regarded as the main contribution to the high crosslinking effectiveness of the P(TAA‒AA)-modified fabrics.

Relationship between Anti-Wrinkle Property of Cotton Fabrics and Crosslinking Properties of Glycosyl Polyaldehydes and Polyuronic Acids Finishing Agents: A Molecular Simulation Study

In this paper, monosaccharide (glucose and fructose), disaccharide (sucrose and trehalose), trisaccharide (raffinose) and tetrasaccharide (stachyose) were selected as the research objects and the glycosyl polyaldehydes and glycosyl polyuronic acid anti-wrinkle finishing agents were prepared via selective oxidation. The anti-wrinkle properties of their finished fabrics were analyzed, the molecular radius, the number of reactive groups, the number of reaction sites and the number of rotatable bonds of the finishing agent were calculated to evaluate its diffusion rate and crosslinking characteristics inside the cellulose. Through molecular simulation, the number of possible conformations of the anti-wrinkle finishing agent with the single cross-linked state was calculated, and the distance between different cross-linking points was measured, and the relationship between the effective cross-linking radius and the anti-wrinkle performance was studied. The results showed that trehalose polyaldehydes, raffinose polyaldehydes, trehalose polyuronic acid, and raffinose polyuronic acid finished fabrics had an excellent anti-wrinkle property, the strength retention rates of the fabrics were all above 68%, and the whiteness index was above 70. The smaller the molecular radius was, the easier the finishing agent was to diffuse into the cellulose. The most suitable crosslinking radius of glycosyl finishing agent was 3.5–6.0 Å.

Effect of Angle Ply On The Mechanical Performance of Jute Fibre Woven Mat /Epoxy Composites With Varying Ageing Conditions

The present work investigates the mechanical strengths retention and prediction of maximum service life of sets of laminated composites by analyzing their diffusion coefficients and activation energies, using Fick’s law and Arrhenius principle. Jute fiber woven mat reinforced epoxy laminated composites (JFMRLCs) were prepared by simple hand lay-up and compression molding methods. The layering patterns of 0º balanced laminate of [0º/0º/0º/0º/0º], 30º angle-ply laminate of [0º/+30º/0º/-30º/0º] and 45° angle-ply laminate of [0°/+45°/0°/-45°/0°] were used to prepare the composite samples, according to classical laminated plate theory (CLPT). The composites were immersed in water at different periods of 10, 20, 30 and 40 days aging. The effects of the various periods of aging on their mechanical properties were studied. The results showed that the weights of the composite samples increased by increasing the aging periods. The mechanical properties of aged (wet) composites were compared with the unaged (dry) counterparts to predict their strengths retention. The composite with 45° layering pattern exhibited the maximum strength retention. Also, the same composite sample with layering pattern of 45° produced the maximum activation energy, based on Arrhenius principle. The tensile fractured surfaces were analyzed to investigate into their fiber-matrix interfacial bonds through images obtained from scanning electron microscopy (SEM). Summarily, it was evident that optimum JFMRLCs with layering pattern of 45° exhibited best mechanical properties. Hence, they can act as suitable, sustainable, low cost and environmentally friendly composite materials for structural marine and other related engineering applications.

Environmental Resistance and Fatigue Behaviors of Epoxy/Nano-Boron Nitride Thermally Conductive Structural Film Adhesive Toughened by Polyphenoxy

The thermally conductive structural film adhesive not only carries large loads but also exhibits excellent heat-transfer performance, which has huge application prospects. Herein, a novel epoxy (Ep) thermally conductive structural film adhesive was prepared using polyphenoxy (PHO) as the toughening agent and film former, boron nitride (BN) nanosheets as the thermally conductive filler, and polyester fabric as the carrier. When the amount of PHO in the epoxy matrix was 30 phr and the content of nano-BN was 30 wt.% (Ep/PHO30/nBN30), the adhesive resin system showed good film-forming properties, thermal stability, and thermal conductivity. The glass transition temperature of Ep/PHO30/nBN30 was 215 °C, and the thermal conductivity was 209.5% higher than that of the pure epoxy resin. The Ep/PHO30/nBN30 film adhesive possessed excellent adhesion and peeling properties, and the double-lap shear strength at room temperature reached 36.69 MPa, which was 21.3% higher than that of pure epoxy resin. The double-lap shear strength reached 15.41 MPa at 150 °C, demonstrating excellent high temperature resistance. In addition, the Ep/PHO30/nBN30 film adhesive exhibited excellent heat-aging resistance, humidity, and medium resistance, and the shear strength retention rate after exposure to the complicated environment reached more than 90%. The structural film adhesive prepared showed excellent fatigue resistance in the dynamic load fatigue test, the double-lap shear strength still reached 35.55 MPa after 1,000,000 fatigue cycles, and the strength retention rate was 96.9%, showing excellent durability and fatigue resistance.

Strength can be controlled by edge dislocations in refractory high-entropy alloys

Energy efficiency is motivating the search for new high-temperature (high-T) metals. Some new body-centered-cubic (BCC) random multicomponent “high-entropy alloys (HEAs)” based on refractory elements (Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr) possess exceptional strengths at high temperatures but the physical origins of this outstanding behavior are not known. Here we show, using integrated in-situ neutron-diffraction (ND), high-resolution transmission electron microscopy (HRTEM), and recent theory, that the high strength and strength retention of a NbTaTiV alloy and a high-strength/low-density CrMoNbV alloy are attributable to edge dislocations. This finding is surprising because plastic flows in BCC elemental metals and dilute alloys are generally controlled by screw dislocations. We use the insight and theory to perform a computationally-guided search over 107 BCC HEAs and identify over 106 possible ultra-strong high-T alloy compositions for future exploration.

Investigation on the Durability of E-Glass/Epoxy Composite Exposed to Seawater at Elevated Temperature

In this manuscript, the durability of the E-glass/epoxy composite was determined under a seawater environment. The effect of harsh environment was investigated in terms of seawater absorption, microstructure and degradation in mechanical properties. E-glass epoxy composite specimens were conditioned in gulf seawater at 23 °C, 65 °C and 90 °C for the period of 12 months. It was observed that the mass of the samples increased after the immersion of 12 months at 23 °C and 65 °C whereas it reduced at 90 °C. The salt deposition was observed at the surface of specimens without any crack for the seawater conditioning at 23 °C and 65 °C. The swelling and crack formation were significantly visible on the surface of the specimen immersed for 12 months at 90 °C. It indicates that the degradation mechanism accelerated at elevated temperature results fiber/matrix debonding. The tensile test indicates slight variation in the elastic modulus and reduction in strength of E-glass epoxy composite by 1% and 9% for specimens immersed at 23 °C and 65 °C respectively. However, at 90 °C, the tensile strength sharply decreased to 7% and elastic modulus significantly increased in the exposure of 12 months. A prediction approach based on a time-shift factor (TSF) was used. This model predicted that the strength retention of E-glass/Epoxy composite will be reduced to 7% in 450 years after immersion in seawater at 23 °C. Lastly, the activation energy for the degradation of the composite was calculated.

Effect of preset interfacial ZrB2 particles on the microstructure and properties of C/C-AlSi composites

ZrB2 particles were preset to the C-AlSi interface to improve oxidation resistance of C/C preform and adjust the microstructure of the interpenetrated C/C-AlSi composite prepared through pressure infiltration of eutectic AlSi into a fiber fabric based porous C/C skeleton. Micro-morphology investigations suggested that the AlSi textures were changed from dendritic to petals-like state, and the nano to micro-scale ZrB2 particles were dispersed into AlSi and affected the distribution of Al and Si nearby carbon. Tests demonstrated that C/C-AlSi have slight lower density and thermal expansion coefficient, and higher original compressive strength, while C/C-ZrB2-AlSi composites presented an outstanding strength retention rate after thermal shock. Fracture and micro-morphology indicated that the influence of the preset ZrB2 to the interface of carbon and alloy greatly affected the generation and propagation of cracks, which determined the diverse compression behaviors of the composites before and after thermal shock.