Mechanical properties of phenol/formaldehyde resin composites reinforced by cellulose microcrystal with different aspect ratio extracted from sisal fiber

Sisal cellulose fiber (SCF) and sisal fiber cellulose microcrystal (SFCM), produced with sulfate pulping method and ball‐milling approach separately, were in‐situ polymerized and dispersed into phenol/formaldehyde (PF) resin, to manufacture SCF/PF and SFCM/PF composites via rolling and molding method and investigate the effect of SCF and SFCM on the impact, flexural, and dynamic mechanical properties of the SCF/PF and SFCM/PF composites. As a result, under the condition of same content, SFCM could preferably enhance these properties maybe resulting from the better dispersion in resin matrix than SCF. In particular, when SFCM content was 7%, the impact strength and equilibrium relaxation modulus of the SFCM/PF composite were increased by 26.5% and 37.7%, while the creep deformation was decreased by 26.5%. In addition, when SFCM content was 5%, the flexural strength, initial storage modulus and glass transition temperature of SFCM/PF composite were increased by 8.5%, 22.6%, and 13°C. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of Layering Pattern on the Mechanical Properties of Bark Cloth (Ficus natalensis) Epoxy Composites

The quest for sustainable materials as a consequence of a global drive to mitigate climate change has led to a focus on natural fiber–reinforced composite materials. In this study, skillful ply angle arrangement of bark cloth–reinforced laminar epoxy composites was carried out for the first time using vacuum-assisted resin transfer molding, and the composites fabricated were characterized for the effect of the layering pattern on their static and dynamic mechanical properties. Tensile strength and flexural strength were shown to be dependent on the ply angle arrangement. Dynamic mechanical analysis of the composites showed a glass transition temperature of 70°C, and the storage modulus and mechanical damping properties showed that the developed composites can withstand considerable loads and have excellent fiber-to-matrix adhesion.     

耐高温可溶性聚酰亚胺树脂及其复合材料

制备了2种耐高温可溶型聚酰亚胺树脂(PI-1, PI-2)及其复合材料, 系统研究了树脂的工艺性, 纯树脂固化物的热性能及其复合材料的界面形貌、 介电性能和力学性能. 研究结果表明, 树脂低聚物在极性非质子溶剂中具有良好的溶解性, 且熔体黏度较低, 表明其具有优异的加工性能. 两种树脂固化物在空气中的5%热失重温度均高于550 ℃, PI-1树脂的玻璃化转变温度(T_g)为430 ℃, PI-2树脂的T_g为380 ℃. 石英纤维/PI-1和石英纤维/PI-2复合材料具有较低的介电常数和介电损耗. 碳纤维/PI-1复合材料在420 ℃下的弯曲强度保持率可达62%, 层间剪切强度保持率可达48%, 具有较优异的高温力学性能. 采用普通模压工艺制备了厚度高达45 mm的复合材料制件, 进一步证明这2种树脂具有优异的工艺性.     

Development of continuous process enabling nanofibrillation of pulp and melt compounding

Microfibrillated cellulose (MFC), a mechanically fibrillated pulp mostly consisting of nanofibrils, is a very attractive material because of its high elastic modulus and strength. Although much research has been done on composites of MFC and polypropylene (PP), it has been difficult to produce such composites at an industrial level because of the difficulties in using MFC in such composites are not only connected to the polarity (that can be improved with compatibilizers), but also with the challenge to make a homogeneous blend of the components, and also the low temperature stability of cellulose that could cause problems during processing. We developed a new processing method which enables continuous microfibrillation of pulp and its melt compounding with PP. Never-dried kraft pulp and powdered PP were used as raw materials to obtain MFC by kneading via a twin-screw extruder. Scanning electron microscopy showed nano to submicron wide fibers entangled in the powdered PP. MFC did not aggregate during the melt compounding process, during which the water content was evaporated. Maleic anhydride polypropylene (MAPP) was used as a compatibilizer to reinforce interfacial adhesion between the polar hydroxyl groups of MFC and non-polar PP. We investigated the effect of MAPP content on the mechanical properties of the composite, which were drastically improved by MAPP addition. Needle-leaf unbleached kraft pulp (NUKP)-derived MFC composites had better mechanical properties than needle-leaf bleached kraft pulp (NBKP)-derived MFC composites. Injection molded NUKP-derived MFC composites had good mechanical and thermal properties. The tensile modulus of 50 wt% MFC composite was two times, and the tensile strength 1.5 times higher than that of neat PP. The heat distortion temperature of 50 wt% MFC content composite under 1.82 MPa flexural load was increased by 53 °C, from 69 to 122 °C. This newly developed continuous process using powder resin has the potential for application at an industrial level.     

Transfer molding imide resins based on 2,3,3′,4′-biphenyltetracarboxylic dianhydride

Phenylethynyl containing imide oligomers have been under investigation as part of an effort to develop resins for non-autoclave composite fabrication processes such as resin transfer molding (RTM). These high performance/high temperature composites are potentially useful on advanced aerospace vehicles such as reusable launch vehicles (RLVs). New phenylethynyl terminated imide oligomers (PETI) based upon 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) were prepared and characterized primarily by rheological behavior and cured glass transition temperature (Tg). In comparison to resins from the symmetrical isomer (3,3′,4,4′-biphenyltetracarboxylic dianhydride, s-BPDA), a-BPDA afforded corresponding resins with lower melt viscosities and upon curing, higher Tgs. Several resins exhibited an attractive combination of properties such as low and stable melt viscosities required for RTM composite fabrication, high cured Tgs, and moderate toughness. One resin (P10) was used to fabricate flat, void free laminates by RTM. The laminates exhibited high mechanical properties at temperatures to 288°C. The chemistry and physical properties of these new PETIs and the laminate properties of one composition are discussed.     

High performance toughened cyanate ester resin with low injection temperature for RTM process

A high‐performance modified cyanate resin system with low injection temperature for fabricating advanced composites via resin transfer molding (RTM) was developed, which was made of bisphenol A dicyanate ester (BADCy) and diallyl phthalate (DAP). The processing characteristics, mechanical, and thermal properties of the resin were studied, and the effect of the content of DAP on the processing and performance parameters was discussed. The results show that the processing properties of the modified cyanate system are dependent on the content of DAP. All the formulations studied in this paper have good processing characteristics; their injection temperatures are between 30 and 40°C and the pot life is about 20 hr at 50°C. The cured resins exhibited good thermal stability, excellent toughness, and good hot–wet resistance, suggesting that the toughened cyanate resin is a potential high‐performance RTM matrix for advanced composites. Copyright © 2008 John Wiley & Sons, Ltd.     

Lignocellulose - polymer composites

Water hyacinth and its mechanical pulps were used as lignocellulose to produce composites together with polystyrene or urea-formaldehyde resins. The bending strength of the composites increased with increasing concentration of the resin. The temperatures of the treatment of water hyacinth to obtain the pulps affect the strength and densities of the composites. This may be attributed to the behavior of lignin at temperatures higher than 135°C. The composites produced using urea-formaldehyde resins showed slight increase in bending strengths compared with those produced using polystyrene, which may be attributed to the ability of formaldehyde to make crosslinks with the free OH groups of cellulose and hemicellulose. Contrary to water hyacinth, the use of ground palm leaves together with 10% urea-formaldehyde resin produced composite with high density and low bending strength, while the ground water hyacinth failed. The pulp from palm leaves when processed into composites using 10% urea-formaldehyde resin show bending and densities affected by its preparation and by the amount of the composite mixture to be pressed. Hence the type of the substrate defined the type of the polymers or resin used to obtain composites with proper mechanical properties. The effect of the pressure used to produce composites from ground palm leaves or their pulp together with polystyrene was investigated. Linear relationships between the bending strength and pressure were obtained, the bending strength and densities increasing with increasing pressure. Thus, the increased pressures enhance mechanical properties of the composites.     

Mechanical Properties,Water Absorption,and Chemical Resistance of Napier Grass Fiber Strand–Reinforced Epoxy Resin Composites

Napier grass fiber strands were used as reinforcement to obtain composites with epoxy resin as matrix. To improve the surface, these fiber strands were treated with alkali solution. The composites were prepared by means of hand lay-up molding, then the effects of Napier grass fiber strand loading on mechanical properties such as tensile, flexural and impact, interfacial bonding, and chemical resistance were investigated. The composite with 20 wt.% Napier grass fiber strands gives excellent mechanical properties and chemical resistance, showing that it has the best bonding and adhesion of the composites. SEM micrographs of fractured and worn surfaces clearly demonstrate the interfacial adhesion between fiber and matrix. Alkali-treated Napier grass fiber strand–reinforced composites have better resistance to water and chemicals than the untreated fiber strand composites.     

纳米SiO_2对高抗冲聚丙烯树脂相结构与性能的影响

提出一种使高抗冲聚丙烯树脂的韧性和刚性同时得到提高的新方法.以亲油性纳米SiO_2改性高抗冲聚丙烯树脂,发现少量纳米SiO_2可显著降低高抗冲聚丙烯树脂中乙丙橡胶相的粒径和聚丙烯相的球晶尺寸,进而使高抗冲聚丙烯的常温韧性、低温韧性、刚性和耐热性同时得到提高.研究还发现,结晶成核剂和纳米SiO_2有协同效应,可使高抗冲聚丙烯的综合性能进一步得到提高.     

纳米花状MnO_2/PPS功能复合滤料的制备及其NH_3-SCR脱硝性能研究

首先采用表面活性剂十二烷基硫酸钠(SDS)对聚苯硫醚(PPS)滤料进行表面活化,由于SDS亲水基团(SO_4~–)与溶液中的H~+发生静电吸附作用,使得之后高锰酸钾在PPS滤料表面原位生成纳米花状二氧化锰,制得nf-MnO_2/PPS复合滤料;并通过探讨高锰酸钾与滤料的质量比、反应时间对nf-MnO_2/PPS复合滤料结构及性能的影响,从而得到最佳制备条件.并利用场发扫描电子显微镜(FESEM)、透射电子显微镜(TEM)、X-射线光电子能谱(XPS)、脱硝活性测试等分析手段对该复合滤料的结构和性能进行了研究;在其基础上利用原位聚合法,在复合滤料表面形成聚吡咯包覆层,制得nf-MnO_2/PPy@PPS复合滤料,并通过多种测试分析手段对改性滤料的结构和性能进行了研究.最后,脱硝测试结果显示,由最佳条件制备出的nf-MnO_2/PPS表现出了最优异的脱硝活性,其在80~180℃时的NO转化率达到36%~100%,nf-MnO_2/PPy@PPS表现出了更好的结合强度和催化稳定性能,但脱硝活性有所下降.     

Investigation of microwave energy to cure carbon fiber reinforced phenylethynyl-terminated polyimide composites,PETI-5/IM7

The application of microwave energy to the processing of carbon fiber reinforced phenylethynyl-terminated polyimide composites (PETI-5/IM7) was investigated and evaluated with a variable-frequency microwave furnace. The thermal and physical properties of the composites were measured by dynamic mechanical thermal analysis, thermogravimetric analysis, thermomechanical analysis, and density and composition tests. The mechanical properties were determined by 3-point-bending and short-beam-shear tests at both room temperature and 177 °C. The shear failure surfaces of both microwave- and thermally cured composites were detected with environmental scanning electron microscopy. A comparison of the thermal and microwave processes was conducted to evaluate the advantage of the microwave process. Microwave-cured composites, fabricated under various pressures at the fixed process temperatures, also were investigated. From these studies, it was concluded that microwave energy successfully was used to fabricate PETI-5/IM7 composites with higher glass-transition temperatures (by 11–16 °C) and higher retention in flexural strength, flexural modulus, and shear strength at 177 °C than those fabricated by the thermal process. Furthermore, the microwave processes required only half the time used for the standard thermal process. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4616–4628, 1999     

Alkoxysilane functionalized polycaprolactone/polysiloxane modified epoxy resin through sol-gel process

Incorporating elastic polysiloxane and/or an inorganic silica network in epoxy resin could result in the enhancement of physico-chemical properties due to the existence of Si-O bonds. To improve the compatibility between polysiloxane and epoxy matrices and intensively strengthen the properties of the modified system, here polysiloxane was introduced into epoxy resin through compatibilizing epoxy-immiscible polysiloxane with epoxy-miscible polycaprolactone segments via a sol-gel process. To fulfill the process, a blend containing alkoxysilane-functionalized polycaprolactone/polydimethylsiloxane (PCS-2Si) was firstly synthesized using direct nucleophilic addition between -OH groups of polydiol and -NCO of a silane. And then a series of modified epoxy resins were prepared in different epoxy/PCS-2Si weight ratios. All the modified composites were characterized by conventional methods, and their morphological, thermal degradation and surface properties were studied. The results showed that increasing the PCS-2Si content caused the changes of miscibility between epoxy and polysiloxane. Also, the thermal stability of the modified composites was greatly improved. As for the temperature value at 5% weight loss, it reached to 308.5 °C for the composite containing 50-60% (wt%) PCS-2Si, over 150 °C higher than that for neat amine-cured epoxy resin. Similarly, the modified composites showed good hydrophobicity. The improvement of these properties came from the improved interaction between PCS-2Si and epoxy, the forming of Si-O-Si network and the enrichment of siloxane chains on the surface of films. Therefore, it is believed that this modified epoxy appears promising as new high performance and highly functional materials.     

碳纳米管及碳纤维增强环氧树脂复合材料研究进展

碳纳米管与碳纤维具有优异的力学、电学等性能,广泛用做复合材料增强体,但目前碳纳米管/碳纤维/环氧树脂复合材料的研究具有一定的局限性,只考虑了两相材料间的作用,即仅对单一相进行处理而忽略了另一相的改性。本文从碳纳米管/碳纤维协同增强环氧树脂基体复合材料的思路入手,结合自己的研究成果,综述了国内外相关研究进展。从研究结果可以看出,将三相材料之间完全有效地联系起来,发挥三者间的协同效应,复合材料的性能可以发生质的飞跃。     

Thermal and mechanical evaluation of cyanate ester resin modified with bismaleimide and diallyl phthalate

Cyanate ester resins have excellent dielectric, mechanical, and thermal properties; however, their major drawback is their brittleness. A high performance matrix blend was developed using bisphenol A dicyanate (BADCy), bismaleimide (BMI) and diallyl phthalate (DAP), and Cobalt (III) acetylacetonate dissolved in nonyl phenol (NP) as a complex catalyst system for BADCy. The properties of the BADCy/BMI/DAP blends, such as thermal and mechanical properties, were investigated in detail by dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and mechanical measurement. The results show that the addition of the appropriate amount of DAP and BMI can improve the impact strength and the flexural strength and this possibly comes from forming an interpenetrating polymer network in the systems. However, the thermal stability of the blends was found to be lower than that of the unmodified BADCy resin. Copyright © 2009 John Wiley & Sons, Ltd.     

Glass fibre sizing effect on dynamic mechanical properties of cyanate ester composites I. Single frequency investigations

In order to investigate sizing effect in composite materials, we studied three types of composites, with different sizings. Dynamic mechanical analysis appeared to be a good way to characterize the α relaxation process of composites and their interphases. Results showed that α relaxation temperature shifted to higher temperatures for composites without sizing. Study of sizing extract/resin blend showed too that interphase was a mixture of polyvinyl acetate and cyanate resin. The results allow us to deduce that a plastification effect of resin by sizing could occur, with modification of crosslink density. Moreover, we can think that all resin is affected by sizing and the conversion rate in interphase is not total.     

High temperature properties of MDF composite based on calcium aluminate cement and polyvinyl alcohol

The macro-defect-free composites belong to the well-known group of promising materials consisting of inorganic binder and organic polymer. MDF composites exhibit unusual mechanical properties, especially the flexural strength that can reach over 200 MPa. Moreover, the MDF composites based on calcium aluminate cement have a good temperature resistance because of the Al₂O₃ content in the cement. This paper deals with the preparation and high temperature characterization of MDF composite based on calcium aluminate cement combined with polyvinyl alcohol that could enable its utilization as a refractory material in industrial kilns. The composition of the MDF mixture has been optimized for an easy high-shear processing and flexural strength of the resulting 7-days cured material has been studied under laboratory condition and after heating at 240, 300, 600, 1,000, and 1,500 °C. The structure changes during the heating have been observed by SEM and the course of processes during the heating has been investigated by TG–DTA–EGA, TMA and heating microscopy.     

Synthesis and characterization of novel phenolic resins containing aryl‐boron backbone and their utilization in polymeric composites with improved thermal and mechanical properties

In the present study, a novel aryl‐boron‐containing phenolic resin named as PBPR has been synthesized from phenol and formaldehyde in the presence of phenylboronic acid. The chemical structure of the PBPR was confirmed by Fourier transform infrared, nuclear magnetic resonance and X‐ray photoelectron spectroscopy. The molecular weight, viscosity and curing behavior were examined to demonstrate that PBPRs have better processability than common boric acid‐modified phenolic resin. The thermal stability and fracture toughness of the cured PBPRs were greatly enhanced, where the char yield at 1000°C (nitrogen atmosphere) and the glass transition temperature reached 70.0% and 218°C, respectively. The excellent mechanical and ablative properties of the PBPR composites may have benefited from the good interfacial adhesion between the resin matrix and the reinforced fiber. The flexural strength and the linear ablative rate are 436.8 ± 5.2 MPa and 0.010 mm/sec, respectively. This study opens a new window for the preparation of high‐performance ablative composites by designing a resin matrix containing an aryl‐boron backbone. Copyright © 2013 John Wiley & Sons, Ltd.     

Mechanical properties and fracture behaviors of C/C composites with PyC/TaC/PyC,PyC/SiC/TaC/PyC multi-interlayers

Carbon/carbon (C/C) composites with PyC/TaC/PyC or PyC/SiC/TaC/PyC multi-interlayers were prepared by isothermal chemical vapor infiltration, followed by Furan resin impregnation and carbonization. Microstructures, mechanical properties including flexural strength, ductile displacement, and fracture behaviors of composites were studied. Furthermore, composites were heat treated at 2000 °C to study the effects of heat treatment on mechanical properties and fracture behaviors. PyC/TaC/PyC and PyC/SiC/TaC/PyC multi-interlayers have been deposited uniformly in C/C composites. With the introduction of PyC/TaC/PyC multi-interlayers in C/C composites, the flexural strength decreases; however, the ductile displacement increases. The fracture behavior changes from brittleness (0% TaC) to pseudo-ductility (5% TaC) and high toughness (10% TaC). When PyC/SiC/TaC/PyC multi-interlayers are introduced in C/C composites, the flexural strength is improved remarkably from 270 MPa to 522 MPa, but the ductile displacement decreases obviously from 0.49 mm to 0.24 mm, and the fracture behavior becomes brittle again. After heat treatment at 2000 °C, the flexural strength decreases, but the ductile displacement increases and pseudo-ductility or high toughness can be obtained.     

Preparation of Low-dielectric Permittivity Polyimide Resins with High Surface Activity from Chemically Bonded Hyperbranched Polysiloxane

Thermosetting resin matrix is the key component of advanced wave-transparent composites,where low dielectric constant,excellent processability,high thermal stability,as well as good bonding ability are required for resins.Herein,we prepared a series of phenylethynyl terminated polyimide(PI)resins by grafting amine-functionalized hyperbranched polysiloxane(HBPSi)to PI chains during the in situ polymerization.The effects of HBPSi on the processability of oligomers,molecular packing,thermal stability,dielectric property and bonding ability to reinforce Kevlar fibers of the cured PI/HBPSi composite resins have been examined in detail.The dielectric constants of the cured composite resins were greatly reduced from 3.29 to 2.19 without compromising its processability and thermal stability.Meanwhile,the 10 wt％HBPSi-containing PI resin demonstrated better bonding ability to reinforce fibers with the interfacial shear strength(IFSS)of 37.64 MPa,compared with that of neat PI-6 matrix(27.34 MPa),and better adhesion to metal with the lap shear strength of 10.48 MPa,50％higher than that of neat resin PI-6(6.98 MPa).These resultant PI/HBPSi composite resins exhibit excellent comprehensive properties,indicating their great potential as low-dielectric constant resin matrix in radar radome.     

Thermomechanical and shape memory properties of SCF/SBS/LLDPE composites

A thermally triggered shape memory polymer composite was prepared by blending short carbon fiber (SCF) into a blend of poly(styrene-b-butadiene-b-styrene) triblock copolymer (SBS)/linear low density polyethylene (LLDPE) prior to curing. These composites have excellent processability compared with other thermosets. The dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) were investigated to assess the thermomechanical properties of the SCF/SBS/LLDPE composite. Scanning electron microscope (SEM) imaging of the samples was performed to show the distribution of the SCF in the composite. The study specifically focused on the effect of SCF on the shape memory behavior of the SCF/SBS/LLDPE composite. The results indicated that the large amount of SCF significantly improved the mechanical property of the polymer composites while not damaging the shape memory performance. The SCF/SBS/LLDPE composites exhibited excellent shape memory behavior when the SCF content was less than 15.0 wt%. Moreover, the shape fixity ratio and shape recovery time of the SCF/SBS/LLDPE composites increased with the SCF content.