The effect of cellulose nanowhiskers on the flexural properties of self-reinforced polylactic acid composites

Self-reinforced polylactic acid (SR PLA) composites incorporating cellulose nanowhiskers (CNWs) were produced by coating orientated PLA fibres with a polyvinyl acetate (PVAc)–CNW mixture as a binder prior to hot compaction at 95 °C. PLA fibres were produced with an average diameter of 11 (±0.9) μm via a melt-drawing process at 180 °C. Scanning electron microscopy (SEM) images revealed that the CNWs imparted roughness to the PLA fibre surface. Cross-sectional examination of the SR PLA composites after hot-pressing confirmed that the PLA fibres had maintained their morphology. Incorporation of 8 wt% CNWs within the SR-PLA composites revealed an increase in their flexural strength (48%) and modulus (39%) compared to the control composite (flexural strength ∼82 MPa and modulus ∼3.9 GPa). In addition, whilst the control SR-PLA composite revealed quite brittle characteristics, the addition of CNWs and PVAc gave the self-reinforced composite a more ductile behaviour.     

Direct transformation of cellulose fibres into self-reinforced composites by partial oxypropylation

Bulk oxypropylation limited to the outer layer of cellulose fibres constitutes a straightforward approach to the preparation of a novel type of composite material made up of a thermoplastic sleeve (matrix) surrounding the unreacted core of the fibres (reinforcing elements).     

Biodegradable fibre reinforced composites composed of polylactic acid and polybutylene succinate

Abstract

Recent concern over the harmful effects on the ecology of long lasting plastics has led to heightened interest in the development of more environmentally sustainable materials. Attention has been paid to biodegradable thermoplastic polymers, polylactic acid (PLA) and polybutylene succinate (PBS). However, although these materials have been widely used as matrix in a composite, the potential of biopolymers as reinforcement in a composite structural system has been examined less. Two types of unidirectional biodegradable composites, PLA self-reinforced and PLA reinforced PBS matrix composites, were produced. The composites were tested for Young’s modulus, tensile strength and strain at break. Cross-section and fracture surface characteristics of the composites were also examined by scanning electron microscopy to identify damage modes. It is found that the tensile strength of both PLA self-reinforced and PLA–PBS composites is increased by 10–40%, while their initial modulus is 2–6 times higher than that measured for PLA and PBS films.     

具有PTC效应的聚合物基复合材料发展概况

本文对具有PTC效应的聚合物基复合材料的导电机理进行概述,并对该类材料的发展概况及研究展望作详细论述。     

Foam-gelcasting preparation of high-strength self-reinforced porous mullite ceramics

High-strength self-reinforced porous mullite ceramics were prepared via foam-gelcasting using mullite powder as a main raw material, AlF₃·3H₂O (0–8 wt%) as an additive, Isobam-104 as a dispersing and gelling agent, sodium carboxymethyl cellulose as a foam stabilizing agent, and triethanolamine lauryl sulfate as a foaming agent. The effects of AlF₃·3H₂O content on rheological and gelling behaviors of the slurries, and porosity and mechanical properties of self-reinforced porous mullite samples were examined. Addition of AlF₃·3H₂O promoted the in-situ formation of elongated mullite in the fired porous samples, which improved considerably their mechanical properties. Compressive strength and flexural strength of 67.0% porous mullite ceramics prepared with addition of 6 wt% AlF₃·3H₂O was as high as 41.3 and 13.9 MPa, respectively. Its hot modulus rupture (HMOR) increased initially with the testing temperature, and peaked (with a maximum value of 16.6 MPa) at 800 °C above which it started to decrease with the testing temperature. Nevertheless, it was still retained as high as 6.7 and 2.8 MPa at 1200 and 1400 °C, respectively.     

Preparation of elongated mullite self-reinforced porous ceramics

Elongated mullite was synthesized using mullite powder as a raw material and AlF₃·3H₂O as an additive, and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The effects of AlF₃·3H₂O content and reaction temperature on the formation of elongated mullite were investigated, and the relevant growth mechanism was discussed based on the experimental results and density functional theory (DFT) calculations. When the optimal amount of AlF₃·3H₂O (4?wt% in the present work) was used, the length and diameter of elongated mullite increased with increasing the reaction temperature, and elongated mullite of 22.3?µm in average length and 4.6?µm in average diameter was formed after 5?h at 1873?K. Based on the results, elongated mullite self-reinforced porous ceramics were prepared by a combined foam-gelcasting and solid-reaction method, and their mechanical properties were examined. Elongated mullite in-situ formed in the porous samples evidently enhanced their mechanical strength. The flexural strength of the elongated mullite self-reinforced porous sample with 67.0% porosity (prepared using 6?wt% AlF₃·3H₂O) was as high as 13.9?MPa, which was about 26.4% higher than that of a porous sample (11.0?MPa) prepared without AlF₃·3H₂O.     

Effects of V2O5 addition on the synthesis of columnar self-reinforced mullite porous ceramics

Spearhead columnar mullite was synthesized by in-situ reaction with V₂O₅ as additive. When the content of V₂O₅ was 7 wt%, the length of the spearhead columnar mullite was the longest with an aspect ratio of about 3.5. Furthermore, columnar self-reinforced mullite porous ceramics were prepared by a foam-gelcasting method, and the effects of V₂O₅ content on the rheological and gelling properties of mullite slurries as well as the microstructure, physical property and thermal insulation property of the prepared mullite porous ceramics were studied. The results showed that the flexural strength and compressive strength of the porous ceramics with 63% porosity prepared by using 2 wt% V₂O₅ additive were respectively as high as 13.9 and 41.3 MPa, and the thermal conductivity was about 1.04 W m^?1 K^?1.     

Effect of PyC interface phase on the cyclic ablation resistance and flexural properties of two-dimensional Cf/HfC composites

Composites based on hafnium carbide and reinforced with continuous naked carbon fiber with and without PyC interface were prepared at low temperature by precursor infiltration and pyrolysis and chemical vapor deposition method. The microstructure, mechanical property, cyclic ablation and fiber bundle push-in tests of the composites were investigated. The results show that after three times ablation cycles, the bending strength of samples without PyC interface decreased by 63.6 %; the bending strength of samples with PyC interface only decreased by 37.8 %. The force displacement curve of the samples with PyC interface presented a well pseudoplastic deformation state. The mechanical behavior difference of two kinds of composites was due to crucial function of PyC interface phase including protection of fiber and weakening of fiber/matrix interface.     

磷酸铝表面修饰及增强双马来酰亚胺复合材料性能

界面行为是决定聚合物基复合材料性能的重要因素之一。首先采用硅烷偶联剂和顺丁烯二酸酐对层状磷酸铝（LAP）逐步修饰制备出表面修饰LAP（m-LAP）；其次利用2，2''-二烯丙基双酚A（DABPA）扩链改性4，4''-双马来酰亚胺基二苯甲烷（BDM）得到双马来酰亚胺（BMI）树脂预聚体；最终利用机械共混法和热固化工艺制备了m-LAP/BMI复合材料。研究发现，m-LAP与BMI基体之间形成了连续、紧密、低缺陷的界面结合。与纯BMI相比，m-LAP/BMI-3.5复合材料的常温弯曲强度为173.37MPa，提高了15.14%；经300℃热处理6h后，m-LAP/BMI-3.5复合材料弯曲强度仍能保持常温强度的71.22%，远高于热处理后的纯BMI树脂及LAP/BMI复合材料；m-LAP/BMI复合材料的玻璃化转变温度（Tg）提高至234~240℃；m-LAP/BMI-3.5复合材料的介电常数达到4.46，介电损耗为0.05。因此，两步表面修饰法能够显著改善LAP/BMI复合材料的综合性能。     

Structural description of self-reinforced polypropylene composites

Self-reinforced polypropylene composites (SR-PP) possess an exceptional property spectrum and are predestined for use in a multitude of structural or semi-structural applications. However, the underlying macromolecular orientation can only be transferred into the layered composites consolidated out of highly stretched fibres and tapes of semi-finished textile products. Specific preservation of the self-reinforcement throughout processing and beyond is necessary and creates special challenges for processing technology. Depending on the processing temperatures and pressures selected, the highly oriented fibres and tapes are influenced by their own degree of self-reinforcement, which, in turn, affects the microstructure and remaining composite properties. In this publication, three different semi-finished textile products are introduced as basic materials. Exemplary selected test samples, which display a low degree of compaction on the one hand and a high degree of compaction on the other, were subject to wet chemical etching to enable confocal laser scanning microscopic images to be created. These images were then used to compare the microstructures of the semi-finished textile products that were used.     

单聚合物复合材料研究进展

综述了单聚合物复合材料的种类、制备方法及其研究现状,着重分析了各种制备方法的优缺点,最后就单聚合物复合材料的前景进行了展望。指出聚砜酰胺基单聚合物复合材料玻璃化转变温度高于300℃,热分解温度超过420℃,热稳定性和阻燃性能均优异,有望成为新一代航空材料;借助静电纺丝技术使材料纳米或微米化,其制备的单聚复合材料力学性能有大幅提高;单聚合物复合材料在航空航天、汽车工业等领域的应用是今后的研究重点;单聚合物复合材料在生物领域有很大的应用前景。     

Decoration of multi-walled carbon nanotubes by polymer wrapping and its application in MWCNT/polyethylene composites

ABSTRACT: We dispersed the non-covalent functionalization of multi-walled carbon nanotubes (CNTs) with a polymer dispersant and obtained a powder of polymer-wrapped CNTs. The UV-vis absorption spectrum was used to investigate the optimal weight ratio of the CNTs and polymer dispersant. The powder of polymer-wrapped CNTs had improved the drawbacks of CNTs of being lightweight and difficult to process, and it can re-disperse in a solvent. Then, we blended the polymer-wrapped CNTs and polyethylene (PE) by melt-mixing and produced a conductive masterbatch and CNT/PE composites. The polymer-wrapped CNTs showed lower surface resistivity in composites than the raw CNTs. The scanning electron microscopy images also showed that the polymer-wrapped CNTs can disperse well in composites than the raw CNTs.     

Surface treatment of wood polymer composites for adhesive bonding

An experimental study was undertaken to evaluate different surface treatment techniques for adhesive bonding of a Wood Polymer Composite (WPC) material. The surface treatment methods were flame, corona discharge treatment (CDT), mechanical abrasion (MA) and combination treatment of MA followed by the CDT. Surface analytical techniques used were contact angle analysis, Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Atomic Force Microscopy (AFM) and 2 dimensional profilometry. Adhesion pull-off test was used to assess the effects of surface treatments. The combination surface treatment, i.e. MA+CDT, was particularly effective in improving bonded joint strength. The adhesion pull-off strengths increased from 0.2 MPa for untreated substrate to 3.4 MPa for MA+CDT treated substrates. The carbonyl, hyroxyl and wood indices obtained from the ATR-FTIR spectra were valuable indicators for studying the nature of WPC substrates.     

Synthesis and characterization of ceramic - polymer composites containing bioactive synthetic hydroxyapatite for biomedical applications

Presented research involved preparation of hydroxyapatite and synthesis of composites based on gelatin, albumin and polyvinylpyrrolidone (PVP) modified with the obtained compound. Hydroxyapatite was attained as a product of two-stage processing of pig bones. Applied procedure involved hydrolysis of the raw material in acidic environment and double calcination. Molar ratio Ca/P of hydroxyapatite has been determined and its chemical structure has been characterized using X-ray diffraction and FT-IR spectroscopy. Ratio Ca/P calculated on the basis of conducted research was 1.50?±?0.05. Thus prepared material met the ISO requirements, which assume that the Ca/P ratio should be in the range 1.5–2.0, which qualifies the material for further studies. Next, series of polymer matrix on the basis of gelatin, albumin and polyvinylpyrrolidone (PVP) has been synthesized and subjected to some analyzes. On the basis of the conducted studies, matrixes with the most favorable features such as desirable strength, flexibility and crosslinking degree were modified with previously prepared hydroxyapatite. Surface morphology and elemental composition of the composites have been analyzed using SEM-EDS method. Additionally, sorption capacity of modified composites and their behavior in simulated body fluids have been determined. Based on the conducted research it can be concluded that pig bones represent a good material for preparation of hydroxyapatite. Furthermore, composites based on proteins of natural origin modified with attained hydroxyapatite constitute a promising material that can be used for biomedical purposes.     

Fabrication of in-situ self-reinforced Si3N4 ceramic foams for high-temperature thermal insulation by protein foaming method

To meet demand for lightweight and high-strength ceramic foams, in-situ self-reinforced Si₃N₄ ceramic foams, with compressive strength of 13.2–45.9 MPa, were fabricated by protein foaming method combined with sintered reaction-bonded method. For comparison, ordinary protein foamed ceramics with irregular block microstructure were fabricated via reaction-bonded method, which had compressive strength of 3.6–20.5 MPa. Physical properties of these two types of samples were systematically compared. When open porosity was about 80%, both types of Si₃N₄ ceramic foams had excellent thermal insulation properties (<0.15 W m^?1 K^?1), while compressive strength of in-situ self-reinforced samples increased by more than 158% compared with ordinary samples. Under high-temperature oxidation conditions, microstructures of both types of samples were deformed with increase in oxidation temperature. Moreover, after oxidation temperature was increased to 1400 °C, oxidation weight gain decreased from 18.07% for ordinary samples to only 2.18% for self-reinforced samples. Thus, high-temperature oxidation resistance of Si₃N₄ ceramic foams was greatly improved.     

Improvement of thermo-electrical properties of polymer composites filled with multiwall carbon nanotubes decorated carbon fillers

To enhance the thermo-electrical properties of liquid silicone rubber (LSR) in applications, the carbon fibres (CFs) modified by multiwall carbon nanotubes (MWCNT) on the surfaces were used as the fillers. The MWCNT-modified CFs (MPCFs) were analysed by Fourier transform infrared spectra, thermogravimetric analysis, scanning electron micrograph and energy dispersive X-ray spectroscopy. It was found that MWCNT were successfully adsorbed onto the surface of CFs. The MPCFs functioned as conductive fillers in LSR for thermal and electrical conductivity application and exhibited significant enhancement. The effects of MPCFs loading on thermal conductivity and volume resistivity of LSR composites were investigated in detail. Results of this work revealed that the MPCFs/LSR composites possessed a thermal conductivity of 0.73?W?m^?1?K^?1 with 14?vol.-% filler loading, approximately 3.48-fold higher than that of pure LSR substrate. And with the increase of MPCFs loading, the least volume resistivity of MPCFs/LSR composites is 10?Ω?cm. Besides, compared with that of neat LSR, the tensile strength of MPCFs/LSR composites increased 0.913?MPa.     

Microwave dielectric properties of PTFE/CaTiO3 polymer ceramic composites

CaTiO₃ ceramic powder filled polytetrafluoroethylene (PTFE) composites with various filler volume fractions up to 60 vol.% were prepared. The effects of volume fraction of the ceramic filler on the microstructure and microwave dielectric properties of the composites were investigated in detail. As the volume fraction of the ceramic filler increases, the dielectric constant (?_r) and the temperature coefficient of resonant frequency (τ_f) of composites increase, while the product of quality factor and frequency (Q × f) decreases. Composites with 40 vol.% CaTiO₃ exhibited good microwave dielectric properties: ?_r = 13 at ∼5 GHz, Q × f = 930 GHz, and τ_f = 260 ppm/°C. Different mixing rules were used to predict the dielectric constant of composites, and it was found that the dielectric constants predicted by Effective Medium Theory (EMT) were in good agreement with experimental data.     

The effect of four methods of surface activation for improved adhesion of wood polymer composites (WPCs)

Wood Polymer Composites (WPCs) have attracted a lot of interest in recent years as materials with a high renewable content. However the adhesion between WPC components is problematic because of low surface energy and the hydrophobic nature of the most widely used polymer matrices, i.e. polyolefins. Thus this paper has looked at four surface activation pretreatment methods to improve adhesion properties for bonding using epoxy adhesives, namely: hydrogen peroxide solution; hot air; a gas flame; and halogen heating lamps. The treatments were applied to WPC materials made from 60% wood flour in a polypropylene matrix, and lap joint shear strength was measured.Shear strength values showed that all treatments except the halogen heating lamps increased the bond strength and the best results were achieved with hydrogen peroxide treatment at a pH of 7.5 (37% improvement); a two pass hot air treatment at a pass speed of 75 mm s⁻¹ (44% improvement); and a gas flame treatment at a pass speed of 175 mm s⁻¹(41% improvement).The bond strength was increased to values that caused failure within the material, rather than at the interfaces of the bond line.     

Synthesis and characterization of chemically and electrochemically prepared conducting polymer/iron oxalate composites

Poly(3-octyl-thiophene) (POT) and polypyrrole (PPy) iron oxalate composites were synthesized through a post-polymerization oxidative treatment. The composite of the latter has been prepared also by electrochemical polymerization. The samples have been characterized by X-ray diffraction (XRD), impedance spectroscopy, scanning electron microscope (SEM) combined with energy dispersive X-ray (EDX) spectroscopy, Mössbauer spectroscopy, cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). In case of PPy, two peaks in the XRD spectra show the presence of iron containing composite, while with POT only the layered structure originating from the octyl side-chain interactions was modified by the composite formation. The assumption of the weakening of short- and long-range interactions was proven by the decrease in conductivity of the composite. The successful electrochemical synthesis resulted a composite of ∼5% iron content, determined by EDX. Mössbauer spectroscopy measurements evidenced a composite containing mixed valence iron oxalate doping ions, which supports the indirect EQCM data.     

Preparation of a novel bi-layer modified alumina-based hybrid material and its effect on the thermal conductivity enhancement of polymer composites

In this work, a new kind of double layers modified alumina-based hybrid (silver@copper@alumina (Ag@Cu@Al₂O₃) hybrid) was successfully synthesized through the two-step layer-by-layer process. First, copper (Cu) nanoparticles were assembled onto alumina (Al₂O₃) particles by reduction of Cu²⁺. Second, Ag@Cu@Al₂O₃ hybrids were assembled via Ag deposition on the surface of Cu@Al₂O₃ particles. The obtained Ag@Cu@Al₂O₃ hybrids served as thermally conductive fillers to greatly boost the thermal conductivity of poly (dimethylsiloxane) (PDMS). The thermal conductivity reached 1.465 W m^?1 K^?1 at 85 wt% filler loading. The thermal conductivity of PDMS matrix was increased more than 7 times by the addition of Ag@Cu@Al₂O₃ hybrid, which was much higher than single layer modified alumina-based hybrids (Ag@Al₂O₃ and Cu@Al₂O₃ hybrids) and virgin Al₂O₃ particle. The effect of double layers modified filler, single layer modified filler and virgin filler on the thermal conductivity of PDMS matrix was discussed in detail and the mechanism of these fillers for improving thermal conductivity was studied through Foygel's thermal conduction model. Otherwise, electric, mechanical and thermal properties of Ag@Cu@Al₂O₃/PDMS composites were also further tested and analyzed.