Preparation of silane precursor microencapsulated intumescent flame retardant and its enhancement on the properties of ethylene–vinyl acetate copolymer cable

Silane precursor microencapsulated intumescent flame retardant (IFR) was prepared by sol–gel process and then modified with vinyltrimethoxysilane (A-171) with the goal of that the vinyl group functionalized silica microcapsule could be introduced into EVA matrix through crosslinking, which will enhance the compatibility and dispersion between EVA matrix and microencapsulated IFR. The effects of silane precursor microencapsulation technology on the mechanical, electrical, thermal, interfacial adhesion and flame retardant properties of intumescent flame-retardant EVA cable were investigated by mechanical test, resistance meter, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), limiting oxygen index (LOI) and UL-94 test. The Fourier transform infrared (FTIR) results indicated silane precursor microencapsulated IFR were successfully prepared, and the water contact angle (WCA) results indicated that silane precursor results in the transformation of hydrophilic to hydrophobic of IFR surface. The characterization for the various properties of EVA composites demonstrated that silane precursor microencapsulation technology enhanced the interfacial adhesion, mechanical, electrical, thermal stability and flame retardancy of EVA/MCAPP/MCPER system. Furthermore, the water resistance test results demonstrate that EVA/MCAPP/MCPER composites have good water durability. This investigation provides a formulation for the industrial application as insulated materials of EVA cable with excellent properties.     

Preparation and properties of microfibrillated cellulose polyvinyl alcohol composite materials

This work reports the preparation of MFC–PVA composite films, and the thermal and mechanical properties of these films. Microfibrillated cellulose (MFC), which was separated from kraft pulp by a mechanical process, was used as the reinforcement in polyvinyl alcohol (PVA) matrix. This MFC reinforcement has an interconnected web-like structure with fibrils having a diameter in the range of 10–100 nm, as observed by TEM. MFC–PVA composite films were created by casting from a water suspension to produce a homogeneous dispersion of MFC in the polymer matrix. DMA shows an increase of the storage modulus in the glassy state with increasing MFC content, but a more significant increase in modulus is detectable above the glass transition temperature. There is a steady increase in both the modulus and strength of the composite films until a plateau is reached at 10 wt% MFC. The thermal stability of the PVA composite films is slightly increased with the addition of MFC.

As a result of this research, it has been shown that MFC is an excellent reinforcement comparable to cellulose nanowhiskers. Furthermore, by combining MFC with PVA in addition to good mechanical properties, this composite has good chemical resistance and biodegradability. The water soluble characteristics of PVA combined with a water dispersion of MFC are also easily processable.     

Preparation and properties of hollow glass microsphere-filled epoxy-matrix composites

Hollow glass microsphere (HGM)–filled epoxy composites, with filler content ranging from 0 to 51.3 vol.%, were prepared in order to modify the dielectric properties of the epoxy. The results showed that the dielectric constant (D_k) and dielectric loss (D_f) of the composites decreased simultaneously with increasing HGM content, which was critical for the provision of superior high-frequency device performance. Other properties of the composite, such as the coefficient of thermal expansion (CTE) and the glass transition temperature (T_g), were also improved. The improvement in these properties was related to strong interaction between the HGM and epoxy, which was indicated by the formation of an interphase between the HGM and epoxy-matrix. It was unsatisfactory in this study that the thermal conductivity of the composites also decreased with HGM content. In order to obtain relatively high thermal conductivity and a low dielectric constant simultaneously, this paper suggests further adding other filler.     

Effects of chitosan as biopolymer coupling agent on the thermal and rheological properties of polyvinyl chloride/wood flour composites

Chitosan (CS) was opted as a novel biopolymer coupling agent for wood flour polyvinyl chloride composites (WF/PVC) to improve interfacial adhesion. This study mainly aimed at investigating the effects after adding CS of different addition amounts and particle sizes on the thermal and rheological properties of WF/PVC composites by the analyses of vicat softening temperature test (VST), differential scanning calorimetry (DSC), thermogravimetry (TGA) and torque rheometry. The results indicated that an optimum addition amount (30 phr) with the particle size (180–220 mesh) could elevate heat resistance capacity, glass transition temperature of composites as well as thermal stability at the early stage of degradation more effectively. In the aspect of rheological characteristics, longer fusion time, lower fusion torque and higher fusion temperature were showed as the CS addition amount increased and the particle size declined. In order to obtain sufficient compaction and ensure proper blending to compounds during extrusion, the higher pressure needed to be supplied when the addition amount of CS exceeded 20 phr.     

Electroactive shape memory polymer based on optimized multi-walled carbon nanotubes/polyvinyl alcohol nanocomposites

The development of shape memory polymers (SMPs) has gained remarkable attention due to their wide range of applications, from biomedical to electromechanical. In this work, we have developed and optimized an electroactive SMP based on polyvinyl alcohol/multi-walled carbon nanotubes (PVA/MWNTs) composites. When a constant voltage of 60 V was applied to the optimized sample, the polymer shape could be recovered to the original form within 35 s. Different weight fractions of MWNT/PVA composites were prepared by using a simple solution blending and transitional solution casting method, and their microstructures, electrical conductivities, thermal conductivities, and electroactive shape memory properties were investigated. According to our systematic analysis, the enhanced performance can be attributed to the reinforcement of MWNTs that led to the improved electrical and thermal conductivities of the PVA matrix.     

Water dispersible graphene noncovalently functionalized with tryptophan and its poly(vinyl alcohol) nanocomposite

Graphene sheets functionalized noncovalently with aromatic amino acid, tryptophan (Tryp), were prepared by reducing graphene oxide through hydrazine hydrate. Tryp-functionalized graphene is water dispersible and can be stabilized for several months. Atomic force microscopy (AFM), X-ray diffraction (XRD), UV–vis absorption and Raman spectroscopy were used to investigate the nanostructures and the properties of graphene. Application of the graphene dispersion to poly(vinyl alcohol) (PVA) with the help of tryptophan to prepare nanocomposite was also carried out. And the PVA/graphene nanocomposite was characterized by thermogravimetric analysis (TGA) and tensile testing. A 23% improvement in tensile strength and moderate increases in Young’s modulus and thermal stability for PVA were achieved by adding only 0.2 wt% graphene sheets.     

Bacterial cellulose-based membrane-like biodegradable composites using cross-linked and noncross-linked polyvinyl alcohol

Bacterial cellulose (BC)-based membrane-like biodegradable composites were produced by immersing wet BC pellicles in polyvinyl alcohol (PVA) solution. The BC content in the BC–PVA composites can be adjusted by varying the concentration of PVA solution. Chemical cross-linking of PVA was carried out using glutaraldehyde to increase the mechanical properties of the composites as well as to make the PVA partially to highly water insoluble. Examination by scanning electron microscopy indicated that the PVA not only penetrated the BC network, but also filled the pores within the BC pellicle. Attenuated total reflectance-Fourier transform infrared spectroscopy showed that acetal linkages could be formed in the BC–PVA composites by a cross-linking reaction. Sol–gel results indicated that cross-linking reaction increasingly made PVA insoluble in water resulting in higher gel (cross-linked fraction) content in the PVA. Wide-angle X-ray diffraction results showed decreased crystallinity in cross-linked BC and PVA, as expected. It was also found that crystal size was smaller in PVA after cross-linking. The BC–PVA composites had excellent tensile properties and cross-linking increased these properties further. Thermogravimetric analysis showed higher thermal stability for BC–PVA composites compared to PVA. The cross-linked specimens, especially the highly cross-linked ones, showed even higher thermal stability. The methods developed in this study make it possible to control the PVA content in the composites as well as the cross-linking level of PVA. These composites could be good candidates for replacing traditional non-biodegradable plastics.     

Layered dielectric–magnetic composite structures for Rf-applications

In this paper multilayer magnetic–dielectric composite structures for high frequency applications are introduced. The 0–3 type dielectric and magnetic composites with homogeneously distributed ceramic inclusions were fabricated by mixing extrusion and injection moulding. Magnetic Yttrium Iron Garnet (YIG) and Z-type Hexaferrite (HexaZ) as well as paraelectric Barium Strontium Titanate (BST) powders were used to enhance the permittivity and permeability of the composites. The magnetic–dielectric multilayer composites were constructed by hot-laminating magnetic and dielectric layers in turn to create a solid 2-2 type composite structure. The microstructure, high frequency dielectric and magnetic properties of individual layers and 2-2 composites were investigated and measured. The measurement results indicate that such multimaterial multilayer structures are good candidates for components with reduced dielectric and magnetic losses. Moreover, the observed good frequency stability and the cut-off frequencies above 1 GHz suggested that the composites could be utilized in, e.g., sophisticated functional circuit boards and RF devices.     

Preparation of thermally reduced graphene oxide and the influence of its reduction temperature on the thermal,mechanical, flame retardant performances of PS nanocomposites

In this article, we investigated the influence of thermally reduced graphene oxides (TGOs) at different reduction temperatures on the thermal, mechanical and flame retardant performances of polystyrene (PS). The results indicated that disordered expanded layer structure can be obtained as the reduction temperature increases from 200 to 500 and 800 °C (the resulted composites are named as PS/TGO2, PS/TGO5 and PS/GTO8, respectively), which could lead to better dispersion of TGO sheets in PS matrix. Dynamic mechanical thermal analysis showed that both the storage modulus and T_g of PS/TGO5 and PS/TGO8 nanocomposites are significantly improved compared with that of neat PS. Noticeable improvement in flame retardant performance were achieved with the addition of TGO5 and TGO8, particularly TGO8, due to the removal of the functional oxygen groups from GO and the barrier effect of intumescent and loosely structure of char layers.     

交联剂对玉米淀粉醋酸酯/PVA可降解复合膜性能的影响

制备了低酯化度玉米淀粉醋酸酯(SA)(DS<0.2)/聚乙烯醇(PVA)可降解复合膜,重点讨论了交联剂的种类、用量、交联反应温度及时间对复合膜力学性能和耐水性的影响。并利用扫描电镜(SEM)X射线衍射(XRD)、热重分析(TG),对复合膜的形貌、结晶度、热稳定性进行表征。结果表明:经过交联后的复合膜,致密性提高,结晶度降低,热稳定性有所增强,表现出更好的力学性能和耐水性。     

Thermo-mechanical properties of poly(vinylidene fluoride) modified graphite/poly(methyl methacrylate) nano composites

Poly(methyl methacrylate) (PMMA) nano composites were synthesized by melt compounding technique. Different graphite loadings were investigated, including some treated with poly(vinylidene fluoride) (PVDF). A homogeneous dispersion of graphite throughout the PMMA matrix was observed under microscopic analysis. Thermo-gravimetric analysis showed the incorporation of graphite resulted in improvement of thermal stability of neat PMMA. Dynamic mechanical thermal analysis also showed a significant improvement in the storage modulus over the temperature range of 25–150 °C. Coating the graphite with a small amount of PVDF was found to further extend the improvement in the modulus of the PMMA nano composite at 1 wt.% graphite loading.     

Hierarchical composites reinforced with robust short sisal fibre preforms utilising bacterial cellulose as binder

A novel robust non-woven sisal fibre preform was manufactured using a papermaking process utilising nanosized bacterial cellulose (BC) as binder for the sisal fibres. It was found that BC provides significant mechanical strength to the sisal fibre preforms. This can be attributed to the high stiffness and strength of the BC network. Truly green non-woven fibre preform reinforced hierarchical composites were prepared by infusing the fibre preforms with acrylated epoxidised soybean oil (AESO) using vacuum assisted resin infusion, followed by thermal curing. Both the tensile and flexural properties of the hierarchical composites showed significant improvements over polyAESO and neat sisal fibre preform reinforced polyAESO. These results were corroborated by the thermo-mechanical behaviour of the (hierarchical) composites, which showed an increased storage modulus and enhanced fibre–matrix stress transfer. Micromechanical modelling was also performed on the (hierarchical) composites. By using BC as binder for short sisal fibres, added benefits such as the high Young’s modulus of BC, enhanced fibre–fibre and fibre–matrix stress transfer can be utilised in the resulting hierarchical composites.     

Thermal stability and tensile properties of sol-enhanced nanostructured Ni–TiO2 composites

A highly-dispersed TiO₂ nano-particles reinforced Ni–TiO₂ composite was prepared by sol-enhanced composite electroplating. The microstructure, thermal stability and tensile properties of the sol-enhanced and traditional Ni–TiO₂ composites were explicitly compared. TiO₂ nano-particles agglomerated to large clusters of ∼400 nm in the traditional Ni–TiO₂ composite. In contrast, nano-sized TiO₂ particles (∼15 nm) were distributed at grain boundaries in the sol-enhanced composite. The grain size, higher micro-strain (∼0.31%) and higher microhardness (∼407 HV₅₀) of the sol-enhanced Ni–TiO₂ composite were stabilized up to 250 °C compared to 150 °C of the traditional composite. The sol-enhanced Ni–TiO₂ composite showed a much higher tensile strength of ∼1050 MPa compared to ∼610 MPa of the traditional composite. The lattice diffusion dominated at high temperatures during grain growth for the sol-enhanced composite. The distribution and location of TiO₂ nano-particles played a significant role in determining the thermal stability and tensile behaviors.     

Microstructure and properties of polyurethane nanocomposites reinforced with methylene-bis-ortho-chloroanilline-grafted multi-walled carbon nanotubes

Methylene-bis-ortho-chloroanilline (MOCA), an excellent cross-linker widely used to prepare cured polyurethane (PU) elastomers with high performance, was used to modify a multi-walled carbon nanotube. PU/carbon nanotube (CNT) nanocomposites were prepared by incorporation of the MOCA-grafted CNT into PU matrix. Fourier transform infrared spectra have shown that the modified CNTs have been linked with PU matrix. The microstructure of composites was investigated by Field-Emission Scanning Electron Microscopy. The results of Dynamic Mechanical Thermal Analysis and Differential Scanning Calorimetry have investigated the grafted CNTs as cross-linker in the cured composites. The studies on the thermal and mechanical properties of the composites have indicated that the storage modulus and tensile strength, as well as glass transition temperature and thermal stability are significantly increased with increasing CNT content.     

Thermal conductive and electrical properties of polyurethane/hyperbranched poly(urea-urethane)-grafted multi-walled carbon nanotube composites

Hyperbranched poly(urea-urethane)-grafted multi-walled carbon nanotubes (HPU-MWCNTs) were incorporated in a polyurethane (PU) matrix based on poly(ethylene oxide-tetrahydrofuran) and aliphatic polyisocyanate resin as curing agent. The 9–12 nm thick HPU shell formed on the MWCNTs improved the dispersion of MWCNTs and enhanced the interfacial adhesion between the PU matrix and MWCNTs, leading to improvements in storage modulus and T_g of the composites and enhancement of the thermal stability of PU. Thus, composites with 0.5–1 wt% MWCNTs increased the thermal conductivity by about 60–70% when compared to, and retained the high electrical resistivity of, neat PU.     

Preparation, structure and mechanical properties of all-hemp cellulose biocomposites

All-hemp (Cannabis Sativa L.) cellulose composites were prepared by a mechanical blending technique followed by hot pressing and water–ethanol regeneration. The alkali treated fibres were ground and sieved to a size ranging from 45 μm to 500 μm. Introduction of fibres into 12% w/v cellulose N-methyl-morpholine-N-oxide (NMMO) solution was performed with low solution viscosity at 100 °C. The solid mixtures were cut and heat pressed between heated glass and PTFE plates at 85 °C to obtain a flat smooth-surfaced composite sheet of approximately 0.2 mm thickness. The cellulose was regenerated in a 50:50 water–ethanol mixture that subsequently removed NMMO and stabilizer (Irganox 1010, Ciba) from the composite. FTIR and X-ray diffraction measurements were performed to investigate the structural change of cellulose from fibre into partially regenerated composite. Composition and thermal stability of composites were investigated using thermogravimetry. A broadening of the scattering of the main crystalline plane (0 0 2) and a depression of the maximum degradation temperature of fibre were observed. The observations revealed a structural change in the fibres. The mechanical properties of composites depended on size, surface area, crystallinity and the structural swelling of fibres.     

Thermal mismatch induced disorder of beta-eucryptite and its effect on thermal expansion of beta-eucryptite/Al composites

In this paper, beta-eucryptite/Al composites with different volume fraction of beta-eucryptite particles (Euc/Al) were prepared by spark plasma sintering process. The microstructures of the composites were studied by transmission electron microscope. The phase compositions and thermal physical properties of the composites were analyzed by X-ray diffraction and thermal dilatometer. The change of peaks intensity ratio of beta-eucryptite (2 0 0) to beta-eucryptite (2 0 2) plane after 12 months of aging in room condition and at elevated temperature (40–300 °C) was used to characterize the disorder of beta-eucryptite, which was due to the high thermal mismatch stress in the composite. The results indicate that the disorder of beta-eucryptite can recover when the thermal mismatch stress in beta-eucryptite is released after 12 months of aging or at elevated temperature. Both compressive stress and tensile stress could induce the disorder of eucryptite (2 0 0) plane. The relationships among CTE behavior of the composite, the phase transformation of beta-eucryptite and the thermal mismatch stress were discussed.     

Interfacially reinforced methylphenylsilicone resin composites by chemically grafting multiwall carbon nanotubes onto carbon fibers

Both silane and multiwall carbon nanotubes (CNTs) were grafted successfully onto carbon fibers (CFs) to enhance the interfacial strength of CFs reinforced methylphenylsilicone resin (MPSR) composites. The microstructure, interfacial properties, impact toughness and heat resistance of CFs before and after modification were investigated. Experimental results revealed that CNTs were grafted uniformly onto CFs using 3-aminopropyltriethoxysilane (APS) as the bridging agent. The wettability and surface energy of the obtained hybrid fiber (CF-APS-CNT) were increased obviously in comparison with those of the untreated-CF. The CF-APS-CNT composites showed simultaneously remarkable enhancement in interlaminar shear strength (ILSS) and impact toughness. Moreover, the interfacial reinforcing and toughening mechanisms were also discussed. In addition, Thermogravimetric analysis and thermal oxygen aging experiments indicated a remarkable improvement in the thermal stability and heat oxidation resistance of composites by the introduction of APS and CNTs. We believe the facile and effective method may provide a novel interface design strategy for developing multifunctional fibers.     

Dynamic compressive behavior of unidirectional IM7/5250-4 laminate after thermal oxidation

Fiber reinforced high temperature polymer matrix composites are currently gaining wide usage in aircraft structures, especially in airframe and engine inlet casing. The failure of composites in worst-case operational conditions mandates the extensive investigation of the mechanical behavior, and the durability in long-term performance and service life under thermal oxidation. In this work, unidirectional IM7 carbon fiber reinforced high-temperature BMI resin composite (IM7/5250-4) were isothermally aged in air for 2 months at 195 °C and 245 °C, respectively. The dynamic behavior of thermally aged composites was investigated on a split Hopkinson pressure bar (SHPB) in three principal directions. The results indicate that thermal oxidation leads to significant reduction in both stiffness and strength of the composites. Optical micrographs of fracture surface and failure pattern of composite after SHPB impact reveals oxidation induced debonding along the fiber–matrix interface due to oxygen diffusion under long-term exposure to elevated temperatures.     

Improvement of properties for biobased composites from modified soybean oil and hemp fibers: Dual role of diisocyanate

An environmentally friendly composite was developed from hemp fibers (HFs) and a biobased thermosetting resin that was formulated from the copolymerization of acrylated epoxidized soybean oil (AESO) and N-vinyl-2-pyrrolidone. The properties of the composites were enhanced through the incorporation of isophorone diisocyanate (IPDI). The FTIR and ¹³C NMR spectra reveal that the incorporated IPDI could react with the hydroxyl groups of both HFs and AESO by forming urethane connections; hence, IPDI plays two roles in composites, i.e., as a crosslinker and a coupling agent. The results show that both effects greatly contribute to increasing the tensile and flexural properties, storage modulus, and glass transition temperature of the resulting composites. However, the modification does not significantly influence the impact strength and slightly decreases the thermal stability of the composites. Further, the addition of IPDI into AESO resins results in resins with improved processability due to the lower viscosity and curing temperature.