Heat treated wood–nylon 6 composites

Heat treatment is a relatively benign modification method that is growing as an industrial process to improve hygroscopicity, dimensional stability and biological resistance of lignocellulosic fillers. There also has been increased interest in the use of lignocellulosic fillers in numerous automotive applications. This study investigated the influence of untreated and heat treated wood fillers on the mechanical and rheological properties of wood filled nylon 6 composites for possible under-the-hood applications in the automobile industry where conditions are too severe for commodity plastics to withstand. In this study, exposure of wood to high temperatures (212 °C for 8 h) improved the thermal stability and crystallinity of wood. Heat treated pine and maple filled nylon 6 composites (at 20 wt.% loading) had higher tensile strengths among all formulations and increased tensile strength by 109% and 106% compared to neat nylon 6, respectively. Flexural modulus of elasticity (FMOE) of the neat nylon 6 was 2.34 GPa. The FMOE increased by 101% and 82% with the addition of 30 wt.% heat treated pine and 20 wt.% heat treated maple, where it reached maximum values of 4.71 GPa and 4.27 GPa, respectively. The rheological properties of the composites correlated with the crystallinity of wood fillers after the heat treatment. Wood fillers with high crystallinity after heat treatment contributed to a higher storage modulus, complex viscosity and steady shear viscosity and low loss factor in the composites. This result suggests that heat treatment substantially affects the mechanical and rheological properties of wood filled nylon 6 composites. The mechanical properties and thermogravimetric analysis indicated that the heat treated wood did not show significant thermal degradation under 250 °C, suggesting that the wood-filled nylon composites could be especially relevant in thermally challenging areas such as the manufacture of under-the-hood automobile components.     

Development of a biocomposite based on green epoxy polymer and natural cellulose fabric (bark cloth) for automotive instrument panel applications

Natural fiber reinforced composites have attracted interest due to their numerous advantages such as biodegradability, dermal non-toxicity and with promising mechanical strength. The desire to mitigate climate change due to greenhouse gas emissions, biodegradable resins are explored as the best forms of polymers for composites apart from their synthetic counterparts which are non-renewable. In this study biodegradable bark cloth reinforced green epoxy composites are developed with view of application to automotive instrument panels. The optimum curing temperature of green epoxy was shown to be 120 °C. The static properties showed a tensile strength of 33 MPa and flexural strength of 207 MPa. The dynamic mechanical properties, frequency sweep showed excellent fiber-matrix bonding of the alkali treated fabric with the green epoxy polymer with glass transition temperature in the range of 160 °C–180 °C. Treatment of the fabric with alkali positively influenced the mechanical properties of the fabric reinforced biocomposites.     

Effects of alkali treatment and elevated temperature on the mechanical properties of bamboo fibre–polyester composites

Bamboo fibre reinforced composites are not fully utilised due to the limited understanding on their mechanical characteristics. In this paper, the effects of alkali treatment and elevated temperature on the mechanical properties of bamboo fibre reinforced polyester composites were investigated. Laminates were fabricated using untreated and sodium hydroxide (NaOH) treated (4–8% by weight) randomly oriented bamboo fibres and tested at room and elevated temperature (40, 80 and 120 °C). An improvement in the mechanical properties of the composites was achieved with treatment of the bamboo fibres. An NaOH concentration of 6% was found optimum and resulted in the best mechanical properties. The bending, tensile and compressive strength as well as the stiffness of this composite are 7, 10, 81, and 25%, respectively higher than the untreated composites. When tested up to 80 °C, the flexural and tensile strength are enhanced but the bending stiffness and compressive strength decreased as these latter properties are governed by the behaviour of resin. At 40 and 80 °C, the bond between the untreated fibres and polyester is comparable to that of treated fibres and polyester which resulted in almost same mechanical properties. However, a significant decrease in all mechanical properties was observed for composites tested at 120 °C.     

Synthesis and properties of sandwiched films of epoxy resin and graphene/cellulose nanowhiskers paper

Graphene (GN)-based composite paper containing 10 wt.% cellulose nanowhiskers (CNWs) exhibiting a tensile strength of 31.3 MPa and electrical conductivity of 16 800 S/m was prepared by ultrasonicating commercial GN powders in aqueous CNWs suspension. GN/CNWs freestanding paper was applied to prepare the sandwiched films by dip coating method. The sandwiched films showed enhanced tensile strength by over two times higher than the neat resins. The moduli of the sandwiched films were around 300 times of the pure resins due to the high content of GN/CNWs paper. The glass transition temperature of the sandwiched films increased from 51.2 °C to 57.1 °C for pure epoxy (E888) and SF (E888), and 49.8 °C to 64.8 °C for pure epoxy (650) and SF (650), respectively. The bare conductive GN/CNWs paper was well protected by the epoxy resin coating, which is promising in the application as anti-static materials, electromagnetic interference (EMI) shielding materials.     

Experimental investigation of high-strain rate properties of 3-D braided composite material in cryogenic field

This paper reports the high-strain rate properties of 3-D braided basalt/epoxy composite materials at 26 °C, −50 °C, −100 °C and −140 °C with strain-rate range from 1300 s⁻¹ to 2100 s⁻¹ by experimental study. A simple and effective cryogenic device was applied to the SHPB system to create the low-temperature field of the samples. It was found that the compression modulus, peak stress, failure strain and specific energy absorption of the 3-D braided basalt/epoxy composite materials had different sensitivity to temperatures and strain rates. In the out-of-plane impact, there were two failure modes, namely, compression-failure mode and shear-failure mode. Fracture of fiber tows was irregular with abundant pull-out of fiber and much finely-divided fragmentation of resin among fibers at room temperature. In cryogenic field, the fracture of fiber tows was neat and tidy with few pull-out of fiber and few finely-divided fragmentation of resin. However, in the in-plane impact, there was only compression failure mode. And there was no fracture of fiber tows and no big difference among samples tested under different gas pressures. Because of the function of squeezing and buckling, split-off separation of the composite could be blocked by the tangled fiber tows. As a whole, the reinforcement could still keep its structural integrity.     

Effects of the high temperature plasma immersion ion implantation (PIII) of nitrogen in AISI H13 steel

In this paper we report the effect of high temperature PIII of nitrogen on the chemical and physical properties of AISI H13 steel. The implantation of H13 steels was carried out at different temperatures ranging between 300 °C and 720 °C. After the treatment, the surface morphology was drastically changed as observed by SEM analysis. Nitrogen penetration depth reaching up to 12 μm was achieved at 620 °C and 720 °C. The maximum hardness of about 592 HV was obtained for the sample treated at 470 °C that is 17% higher than for untreated specimen. There was a decrease of the hardness values for temperatures above 470 °C. The same hardness behavior with the temperature was confirmed by nanoindentation testing. Although an enriched nitrogen layer was obtained, no evidence of nitride compounds was detected by XRD analyses. On the other hand, improvements of the H13 steel tribological properties and corrosion resistance were obtained. The wear tests were conducted by pin-on-disk tribometer (rotating mode). The wear volume decreased by factor of 4.5 compared to the standard tempered and annealed H13 steel and 2.6 times reduction of the coefficient of friction was achieved. The electrochemical measurements were performed in 3.5% NaCl solution, pH = 6. Open circuit potential curves showed that the potentials are nobler for the PIII treated samples than for untreated specimen. In addition, the corrosion current density of the samples treated at 620 °C and 720 °C diminished to 3 × 10⁻⁸ A/cm².     

Graphitization behavior of iodine-treated <Emphasis Type="Italic">Bombyx mori</Emphasis> silk fibroin fiber

In order to investigate the graphitization behavior of Bombyx mori silk fibroin (SF) fibers, structural inspection of carbonized SF fibers treated with iodine vapor was studied at different temperatures, from 800 to 1400 °C. Wide angle X-ray diffraction measurement suggested that both untreated and iodinated SF fibers exhibited amorphous structure carbonized to 1200 °C. After carbonization at 1400 °C for 12 h, a graphite-like structure was obtained. Raman spectroscopy and transmission electron microscopic observation showed that the graphite layers of SF fibers became more ordered after iodine treatment. The carbon yield obtained at higher temperature (1400 °C) after iodine treatment was higher, ca. 28 wt%, than that of untreated SF.     

Fabrication and characterization of n-type aluminum-boron co-doped ZnO on p-type silicon (n-AZB/p-Si) heterojunction diodes

In this paper, the growth of n-type aluminum boron co-doped ZnO (n-AZB) on a p-type silicon (p-Si) substrate by sol–gel method using spin coating technique is reported. The n-AZB/p-Si heterojunctions were annealed at different temperatures ranging from 400 to 800 °C. The crystallite size of the AZB nanostructures was found to vary from 28 to 38 nm with the variation in annealing temperature. The band gap of the AZB decreased from 3.29 to 3.27 eV, with increasing annealing temperature from 400 to 700 °C and increased to 3.30 eV at 800 °C probably due to the formation of Zn₂SiO₄ at the interface. The band gap variation is explained in terms of annealing induced stress in the AZB. The n-AZB/p-Si heterojunction exhibited diode behavior. The best rectifying behavior was exhibited at 700 °C.     

Fabrication and characterization of three-dimensional PMR polyimide composites reinforced with woven basalt fabric

A PMR polyimide composite reinforced with three-dimensional (3D) woven basalt fabric is fabricated for medium high temperature applications. The PMR polyimide matrix resin is derived from 4,4′-methylenediamine (MDA), diethyl ester of 3,3′,4,4′-oxydiphthalic (ODPE) and monoethyl ester of Cis-5-norbornene-endo-2,3-dicarboxylic acid (NE). The rheological properties of the PMR polyimide matrix resin are investigated. Based on the curing reaction of the PMR type polyimide and the rheological properties, an optimum two-step fabrication method is proposed. The three dimensional fabric preforms are impregnated with the polyimide resin in a vacuum oven at 70 °C for 1 h followed by removing the solvent and pre-imidization. The composites are then consolidated by an optimized molding procedure. Scanning electron microscopy analysis shows that needle shaped voids are generated in yarns and the void volume fraction is 4.27%. The decomposition temperature and the temperature at 5% weight loss of the composite post-cured at 320 °C for 24 h are 440 °C and 577 °C, respectively. The dielectric constant and the dielectric loss of the composite are measured by circular cavity method at 7–12 GHz. The tensile strength and the modulus in the warp direction of the composite are 436 MPa and 22.7 GPa. The composite shows a layer-by-layer fracture mode in three-point bending test. The flexure strength and modulus in the warp direction of the composite are 673 MPa and 27.1 GPa, respectively.     

Enhanced thermal conductivity and retained electrical insulation for polyimide composites with SiC nanowires grown on graphene hybrid fillers

Polyimide (PI) composites containing one-dimensional SiC nanowires grown on two-dimensional graphene sheets (1D–2D SiC_NWs-GSs) hybrid fillers were successfully prepared. The PI/SiC_NWs-GSs composites synchronously exhibited high thermal conductivity and retained electrical insulation. Moreover, the heat conducting properties of PI/SiC_NWs-GSs films present well reproducibility within the temperature range from 25 to 175 °C. The maximum value of thermal conductivity of PI composite is 0.577 W/mK with 7 wt% fillers loading, increased by 138% in comparison with that of the neat PI. The 1D SiC nanowires grown on the GSs surface prevent the GSs contacting with each other in the PI matrix to retain electrical insulation of PI composites. In addition, the storage modulus and Young’s modulus of PI composites are remarkably improved in comparison with that of the neat PI.     

Thermo-mechanical behaviour and structure of novel bitumen/nanoclay/MDI composites

Novel ternary bituminous composites have been prepared by mixing neat bitumen with an organically modified montmorillonite (Cloisite 20A^®) and polymeric MDI (diphenylmethane diisocyanate). Rheological measurements (flow curves and temperature sweeps in oscillatory shear), X-Ray diffraction, Atomic Force Microscopy (AFM) and Fourier Transform Infrared Spectroscopy (FTIR) were used to analyse the individual and joint effects of both modifiers. The results obtained show that the addition of 10 wt.% nanoclay provokes a very remarkable enhancement in the bitumen rheological response. The addition of 2 wt.% MDI and subsequent curing at 150 °C, resulting from the chemical interaction between the bitumen/clay composite and MDI, improves the composite properties at low-to-intermediate temperatures but deteriorates them when temperature is further increased.     

Tri-Layered Bicomponent Microfilament Composite Fabric for Highly Efficient Cold Protection

Functional thin fabric with highly efficient cold protection properties are attracting the great attention of long-term dressing in a cold environment. Herein, a tri-layered bicomponent microfilament composite fabric comprised of a hydrophobic layer of PET/PA@C₆F₁₃ bicomponent microfilament webs, an adhesive layer of LPET/PET fibrous web, and a fluffy-soft layer of PET/Cellulous fibrous web is designed and also successfully been fabricated through a facile process of dipping, combined with thermal belt bonding. The prepared samples exhibit a large resistance to wetting of alcohol, a high hydrostatic pressure of 5530 Pa, and brilliant water slipping properties, owing to the presence of dense micropores ranging from 25.1 to 70.3 µm, as well as to the smooth surface with an arithmetic mean deviation of surface roughness (Sa) ranging from 5.112 to 4.369 µm. Besides, the prepared samples exhibited good water vapor permeability, and a tunable CLO value ranging from 0.569 to 0.920, in addition to the fact that it exhibited a very suitable working temperature range of −5 °C to 15 °C. Additionally, it also showed excellent clothing tailorability including high mechanical strength with a remarkably soft texture and lightweight foldability that suitable for cold outdoor clothing applications.     

Preparation and properties of self-reinforced poly(lactic acid) composites based on oriented tapes

The inherent brittleness and poor thermal resistance of poly(lactic acid) (PLA) are two main challenges toward a wider industrial application of this bioplastic. In the present work, through the development of self-reinforced PLA (SR-PLA) or “all-PLA” composites, the high brittleness and low heat deflection temperature (HDT) of PLA have been overcome, while simultaneously improving the tensile strength and modulus of SR-PLA. The obtained composites are fully biobased, recyclable and under the right conditions compostable. For the creation of SR-PLA composites, first a tape extrusion process was optimized to ensure superior mechanical properties. The results show that SR-PLA composites exhibited enhanced moduli (2.5 times) and tensile strengths (2 times) and showed 14 times increase in impact energy compared to neat PLA. Finally, the HDT of SR-PLA was also increased by about 26 °C compared to neat PLA, mainly as a result of an increase in modulus and crystallinity.     

Effect of hygrothermal ageing on morphology and indentation modulus of injection moulded nylon 6/organoclay nanocomposites

The effect of water immersion on the morphology and indentation modulus of injection moulded nylon 6 and its organoclay nanocomposites was investigated. XRD analysis showed that at 70 °C water promoted further crystallization in the nylon matrix and aided the γ- to α-crystal phase transition in the skin region. However, the presence of organoclay deterred this transformation. The combined actions of water and heat (70 °C) did not further degrade nylon 6 and its nanocomposites compared to water ageing at room temperature (25 °C). In fact, there was relative enhancement of the indentation moduli owing to the beneficial morphological changes induced in the nylon matrix. The largest improvements were found in the skin region of the injection moulded bars.     

Cure path dependency of mode I fracture toughness in thermoplastic particle interleaf toughened prepreg laminates

The effect of cure cycle on fracture behaviour of a commercial thermoplastic particle interleaved prepreg system was investigated. Laminates were manufactured at 700 kPa in an autoclave using eight different thermal cycles that included both raising the cure temperature above the standard 180 °C cure cycle and incorporating an intermediate dwell stage between 150 and 170 °C prior to reaching the 180 °C cure temperature. Double cantilever beam tests were conducted on specimens from the cured laminates. The stick–slip crack behaviour, observed in samples manufactured using the standard cure cycle, changed to stable crack growth when processing deviated by 10 °C. The mode I fracture toughness values were reduced by 11–22% when incorporating an intermediate dwell stage before the final cure temperature. Scanning electron microscopy inspection of the fracture surfaces showed differences between samples made by standard cure cycles and those made using process deviations.     

Multiscale fiber reinforced composites based on a carbon nanofiber/epoxy nanophased polymer matrix: Synthesis, mechanical, and thermomechanical behavior

Vacuum assisted resin infusion molding (VARIM) was used to produce multiscale fiber reinforced composites (M-FRCs) based on carbon nanofibers dispersed in an epoxy resin. Flexural, interlaminar shear strength (ILSS) and thermomechanical tests are presented for the 0.1 wt% and 1 wt% M-FRCs and compared with the neat fiber reinforced composites (FRCs). Flexural strength and modulus increased (16–20%) and (23–26%), respectively for the 0.1 wt% and 1 wt% M-FRCs when compared to the neat FRCs. ILSS properties increased (6% and 25%) for the 0.1 wt% and 1 wt% M-FRCs, respectively when compared to neat FRCs. The glass transition temperatures (T_g) of both M-FRC samples were 25 °C higher than the neat FRC. Coefficients of thermal expansion (CTE) of the M-FRC samples improved compared to the neat FRC. The improved T_g and CTE properties in the M-FRC samples are attributed to synergistic interactions between the CNF/PNC matrix and glass fibers.     

Effects of temperature and clay content on water absorption characteristics of modified MMT clay/cyclic olefin copolymer nanocomposite films: Permeability,dynamic mechanical properties and the encapsulated organic device performance

In the present study, amino-silane modified layered organosilicates were used to reinforce cyclic olefin copolymer to enhance the thermal, mechanical and moisture impermeable barrier properties. The optimum clay loading (4%) in the nanocomposite increases the thermal stability of the film while further loading decreases film stability. Water absorption behavior at 62 °C was carried out and compared with the behavior at room temperature and 48 °C. The stiffness of the matrix increases with clay content and the recorded strain to failure for the composite films was lower than the neat film. Dynamic mechanical analysis show higher storage modulus and low loss modulus for 2.5–4 wt% clay loading. Calcium degradation test and device encapsulation also show the evidence of optimum clay loading of 4 wt% for improved low water vapor transmission rates compared to other nanocomposite films.     

Enhanced stress transfer and thermal properties of polyimide composites with covalent functionalized reduced graphene oxide

This work prepares (3-aminopropyl) trimethoxysilane (APTMS)-functionalized reduced graphene oxide (APTMS-rGO)/polyimide (PI) composite (APTMS-rGO/PI) through in-situ polymerization. NH₂-functionalized rGO coupled by APTMS demonstrates the good reinforced efficiency in mechanical and thermal properties, which is ascribed to the covalent-functionalized PI matrix by APTMS-rGO sheets. The uniform dispersion of APTMS-rGO increases the glass transition temperature (Tg) and the thermal decomposition temperature (Td), exhibiting 21.7 °C and 44 °C improvements, respectively. The tensile strength of the composites with 0.3 wt% APTMS-rGO is 31% higher than that of neat PI, and Young’s modulus is 35% higher than that of neat PI. Raman spectroscopy show the obvious G band shift, and also clearly demonstrates the enhanced interfacial interaction between rGO nanofillers and PI matrix. The high mechanical property of the APTMS-rGO/PI composites is attributed to the covalent functionalized GO by NH₂ groups and its good dispersion in comparison with GO.     

The effect of processing temperature and placement rate on the short beam strength of carbon fibre–PEEK manufactured using a laser tape placement process

The ability of a modern near infra-red laser tape placement system to produce high-quality laminates is investigated by performing short beam strength tests on samples manufactured at different process temperatures from 400 °C to 600 °C at placement rates of 100 mm/s and 400 mm/s. The temperature history in tape placement is highly dynamic and the correlation between the process control temperature, laser power and the consolidation temperature is not well understood. The complete temperature history was therefore estimated with a previously developed optical-thermal model and validated using long wave infra-red imaging. Short beam strengths equivalent to conventional manufacturing methods were found for placement rates of 400 mm/s. Failure modes of the samples were elucidated by scanning electron microscopy of the fracture surfaces. Signs of degradation were observed on samples prepared with a 600 °C process temperature at 100 mm/s, however none was evidenced at 400 mm/s for the same process temperature.     

Graphite-like carbon nitride and functionalized layered double hydroxide filled polypropylene-grafted maleic anhydride nanocomposites: Comparison in flame retardancy,and thermal,mechanical and UV-shielding properties

Graphite-like carbon nitride (g-C₃N₄) and borate modified layered double hydroxides (LDH-B) were successfully fabricated by thermal pyrolysis and modified aqueous miscible organic solvent treatment methods, respectively. Then these nano-additives were introduced to prepare polypropylene-grafted maleic anhydride (PP-g-MA)/g-C₃N₄ and PP-g-MA/LDH-B nanocomposites using a modified solvent mixing strategy. Several important parameters of the nanocomposites including thermal, mechanical and UV-blocking properties were investigated. Results indicated that pure g-C₃N₄ exhibited 347.6 and 427.2 °C increase in onset decomposition temperature under air and nitrogen conditions, respectively, compared with LDH-B. In case of PP-g-MA nanocomposites, both T_-10 and T_-50 (the temperature at 10% and 50% weight loss, respectively) were improved by 14.6 and 27.7 °C, respectively, by the addition of g-C₃N₄ while those only increased by 2.3 and 17.8 °C upon introducing LDH-B. Furthermore, PP-g-MA/g-C₃N₄ system showed a remarkable increment (9.8 °C) in crystallization temperature while an increase of 4.2 °C for PP-g-MA/LDH-B nanocomposite. Introducing g-C₃N₄ and LDH-B into PP-g-MA led to a reduction of 28% and 19% in pHRR, respectively. It was noted that the incorporation of g-C₃N₄ caused significant improvement in storage modulus from 2445.0 MPa for neat PP-g-MA to 2783.5 MPa for PP-g-MA/g-C₃N₄ while that of PP-g-MA/LDH-B was dramatically decreased by 27.3%. Optical results indicated that PP-g-MA/g-C₃N₄ was rendered fascinating UV adsorption ability relative to PP-g-MA/LDH-B. It is expected that the novel two-dimensional nanomaterial could bring new creativity into polymer composites.