MFC-structured biodegradable poly(l-lactide)/poly(butylene adipate-co-terephatalate) blends with improved mechanical and barrier properties

Both polylactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) are biodegradable polymers. They are thermoplastics which can be processed using conventional polymer processing methods. In this study, microfibrillar-reinforced composites (MFC) based on PLA/PBAT (PLA/Ecoflex^®) blends in different weight ratios were prepared under industry-relevant conditions by melt extrusion followed by continuous cold drawing of the extrudates. Strip-like specimens (films) and plates (laminates) of the drawn blends were prepared by compression molding (CM) at processing temperature above the melting temperature (T _m) of PBAT, but below T _m of PLA. SEM and WAXS observations show that the extruded blend components are isotropic, but become highly oriented after drawing, and they are converted into MFC-structured polymer–polymer composites after CM. An effect of PLA microfibrils on the non-isothermal crystallization of the Ecoflex during cooling from the melt, associated with the formation of crystalline regions of the matrix around the fibrils, was observed. Depending on the blend composition, the compression-molded samples possess a 3- to 7-time higher tensile strength as well as a 15–30 higher modulus than the neat Ecoflex. In addition, the MFC-structured plates exhibited superior barrier properties compared to the neat Ecoflex, e.g., the oxygen permeability decreased by up to 5 times.     

微观结构对中间相沥青基炭/炭复合材料力学性能的影响

借助偏光显微镜、扫描电镜、透射电镜以及力学性能测试研究了微观结构对中间相沥青基炭/炭复合材料力学性能的影响. 结果表明: 基体炭在偏光显微镜下呈现出光学各向异性, 在SEM和TEM下呈片层条带状结构. 基体炭与纤维之间的界面不连续, 为“裂纹型”界面. 材料受载破坏时裂纹通过改变扩展路径而延缓其扩展速度, 在纤维-基体界面处以及基体炭层片之间引起滑移, 在断口形貌上体现出断裂台阶适中且与纤维拔出交替进行, 表现出韧性破坏的断裂特征. 材料具有较高的力学性能, 抗弯强度达到257MPa, 断裂韧性达到11.4MPa·m ^1/2.     

Microfibril reinforced polymer–polymer composites: Application of Tsai-Hill equation to PP/PET composites

In this paper an attempt has been made to check the extent of validity of the Tsai-Hill equation applied to polymer–polymer microfibril reinforced composites (MFCs), in which the reinforcing elements represent microfibrils with diameters around 1 μm and aspect ratios of approximately 100. For this purpose compression moulded plates of polypropylene/poly(ethylene terephthalate: 70/30 by wt%) composites have been prepared and their structures are established by wide angle X-ray scattering and scanning electron microscope (SEM) analysis. The tensile tests of cut specimens at various angles ( with respect to the uniaxially aligned microfibrils) show the degree of agreement with Tsai-Hill predictions. The measured values are slightly higher than the calculated ones and this finding is explained by the higher aspect ratios of microfibrils, their more homogenous distribution and most importantly, by the better matrix/reinforcement adhesion in the case of MFCs as compared to the common composites. The fracture mechanism as determined from the SEM observations on the fracture surfaces is also discussed and a good agreement with the mechanical behaviour is found.     

Investigation of the effect of addition of calcium stearate on the properties of low-density polyethylene/poly(ε-caprolactone) blends

Low-density polyethylene (LDPE) was blended with poly(ε-caprolactone) (PCL), prepared in proportions of 75/25, 50/50, and 25/75 (LDPE/PCL, wt/wt%). The effect of the addition of calcium stearate (CaSt) of these polymers was assessed by melting flow index, differential scanning calorimetry, tensile test, scanning electron microscopy (SEM), biodegradation in simulated soil with calcium determination, and enzymatic degradation. The addition of CaSt reduced the MFI of the PCL and of the 75/25 blend. The incorporation of 25 % of PCL slightly increased the T _m of LDPE. The tensile strength had no significant changes with the addition of CaSt and the polymers showed that they are incompatible according to this property. SEM showed poor interfacial interaction between PCL and LDPE, as well as that they are immiscible, and showed no significant changes on the morphology of the materials with the addition of CaSt. The results show that polymer samples after biodegradation in simulated soil present more calcium content than initial samples polymer. The soil analysis shows that the soil that contains the polymers submitted to thermal aging show smaller calcium content than the samples that were not aged. Lipase enzyme reinforced its specificity over PCL, and the addition of CaSt reduced the degradation of PCL and the 75/25 PCL/LDPE blend, however, it increased the rate of degradation of 50/50 and 25/75 blends.     

Interfacial adhesion improvement of plain woven carbon fiber reinforced epoxy filled with micro-fibrillated cellulose by addition liquid rubber

In certain application of fiber reinforced polymer composites fracture resistance is required. The aim of this study was to improve the interfacial adhesion between plain woven carbon fiber (CF) and epoxy matrix filled with microfibrillated cellulose (MFC) modified with carboxyl-terminated butadiene acrylonitrile (CTBN) as liquid rubber. CF/Epoxy/MFC/CTBN composite was characterized by different techniques, namely, tensile, bending, fracture toughness (mode I) test, and scanning electron microscope (SEM). The results reveal that at a fiber content 1% of MFC and 10% CTBN, initiation and propagation interlaminar fracture toughness in mode I improved significantly by 96 and 127%, respectively, which could be attribute to strong adhesion between filled epoxy, CF, and rubber. This can be explained by SEM at given weight as well; SEM images showed that in front of the tip, fiber breakage during initiation delimination as well as the extensive matrix deformation between fibers accounting for increase fracture toughness.     

Evolution of morphology in high molecular weight polyethylene during die drawing

Deformed high molecular weight polyethylene (HMWPE) rod, formed by die drawing at 115C, was cleaved longitudinally at liquid nitrogen temperature and the cleaved surface was etched by the permanganic etching technique, A series of etched surfaces of HMWPE sections of variable draw ratio (1–13) was analysed by scanning electron microscopy (SEM), The evolution of crystalline structure in HMWPE during die drawing was observed directly. In undrawn HMWPE, the spherulites were made up of sheaf-like lamellae and scattered within an amorphous phase. During die drawing, first, microscopically inhomogeneous deformation occurred and the spherulites aligned along the drawing direction; then at a draw ratio of about 7, local melting occurred, the spherulites disintegrated and the sheaf-like lamellae oriented, followed by strain-induced recrystallization and the growth of the lamellae; finally, at a draw ratio of about 12, plastic deformation of the lamellae occurred and microfibrils were formed by drawing the lamellae.     

Sliding performance of polymer composites in liquid hydrogen and liquid nitrogen

Outstanding features favour the application of polymers and polymer composites in low-temperature technology. The booming hydrogen technology is a challenge for these materials, which are considered as seals and bearings in cryogenic pumps. In the present study, three types of thermoplastics, i.e., polyetheretherketone (PEEK), polyetherimide (PEI) and polyamide 6,6 (PA6,6), and one epoxy were considered as matrix materials. Micron-sized fillers, i.e., short carbon fibres, graphite flakes, and PTFE powders, were incorporated into these polymers together with nano-sized TiO₂ particles. Optimised compositions of each matrix were selected from our previous works at room temperature in order to be studied at very low temperature conditions. In particular, frictional tests were carried out with polymer composite pins against polished steel surfaces under constant load over a certain distance in liquid hydrogen and liquid nitrogen. Afterwards, worn surfaces were analysed by using scanning electron microscopy (SEM). It was found out that the tribological properties in liquid hydrogen are dominated by the matrix materials, in particular thermoplastics perform generally slightly better than thermosetting resins.     

Solvent exfoliated graphene for reinforcement of PMMA composites prepared by in situ polymerization

Graphene (GP)-based polymer nanocomposites have attracted considerable scientific attention due to its pronounced improvement in mechanical, thermal and electrical properties compared with pure polymers. However, the preparation of well-dispersed and high-quality GP reinforced polymer composites remains a challenge. In this paper, a simple and facile approach for preparation of poly(methyl methacrylate) (PMMA) functionalized GP (GPMMA) via in situ free radical polymerization is reported. Fourier transform infrared (FTIR), X-ray photoelectron spectra (XPS), Raman, transmission electron microscope (TEM) and thermogravimetric analysis (TGA) are used to confirm the successful grafting of PMMA chains onto the GP sheets. Composite films are prepared by incorporating different amounts of GPMMA into the PMMA matrix through solution-casting method. Compared with pure PMMA, PMMA/GPMMA composites show simultaneously improved Young's modulus, tensile stress, elongation at break and thermal stability by addition of only 0.5 wt% GPMMA. The excellent reinforcement is attributed to good dispersion of high-quality GPMMA and strong interfacial adhesion between GPMMA and PMMA matrix as evidenced by scanning electron microscope (SEM) images of the fracture surfaces. Consequently, this simple protocol has great potential in the preparation of various high-performance polymer composites.     

PET/PE原位微纤化共混物的非等温结晶

通过挤出、热拉伸及淬冷制备了聚对苯二甲酸乙二醇酯(PET)/聚乙烯(PE)原位微纤化共混物。采用差示扫描量热仪(DSC)研究了PET/PE原位微纤化共混物的非等这结晶特性,为了比较,同时考察了纯PE和PET/PE通常共混物的结晶特性。结果表明,PET微纤对PE有良好结晶异相成核作用,可提高结晶温度、缩短结晶时间、增大结晶速率,但使PE的结晶度和熔点降低;增加降温速率,结晶峰变宽且向低温方向移动。     

Preparation and properties of carbon black/polymer composites with segregated and double-percolated network structures

A carbon black (CB)/low-density polyethylene (LDPE)/ultrahigh-molecular-weight polyethylene (UHMWPE) composite with a segregated and double-percolated structure has been fabricated using the solution mixing and high-speed mechanical mixing method. Structural observations show that the conducting CB/LDPE layers were only dispersed at the interface of UHMWPE granules and formed a well-developed CB conductive network with a percolation threshold of 0.26 vol%. The low percolation threshold in CB/LDPE/UHMWPE composites can be explained by the segregated and double-percolated networks of CB within the polymer matrix. A noticeable double positive temperature coefficient of resistivity can be observed around the melting temperature of LDPE and UHMWPE followed by a negative temperature coefficient of resistivity. The microstructure evolution of CB/LDPE/UHMWPE composites can be observed and explained by in situ optical micrographs.     

Microstructure,flexural properties and durability of coir fibre reinforced concrete beams externally strengthened with flax FRP composites

This study investigated the flexural behaviour of plain concrete (PC) and coir fibre reinforced concrete (CFRC) beams externally strengthened by flax fabric reinforced epoxy polymer (FFRP) composites. PC and CFRC beams without and with FFRP (i.e. 2, 4 and 6 layers) reinforcement were tested under three- and four-point bending. The microstructures of coir fibre, coir/cement matrix, flax/epoxy matrix, and FFRP/concrete interfaces were analysed using scanning electronic microscope (SEM). Test results indicated that the peak load, flexural strength, deflection and fracture energy of both PC and CFRC specimens enhanced proportional to an increase of FFRP layers. Coir further increased load, strength and energy of the specimens remarkably. It was also found that the thickness and coir influenced the failure modes while the test method influenced the load and energy of the specimens remarkably. SEM studies showed effective bond at coir/cement, flax/epoxy and FFRP/concrete interfaces. Therefore, it concluded that natural FFRP composites can be used to repair or retrofit existing concrete structures.     

炭黑填充PET/PE导电原位微纤化复合材料

根据炭黑（CB）粒子在聚合物中的选择性分布理论,通过工艺控制,使CB粒子主要分布在微纤表面。本工作将CB粒子首先与聚乙烯（PE）共混,再与聚对苯二甲酸乙二醇酯（PET）熔融混合-挤出-热拉伸-淬冷。形态观察表明,CB粒子可以良好地分布于PET微纤表面。电性能测试表明,分布于微纤表面的CB粒子有助于微纤之间的电子传导,该复合材料的正温度系数（PTC）较强,而负温度系数（NTC）较弱。     

Study on dispersion and electrical property of multi-walled carbon nanotubes/low-density polyethylene nanocomposites

Sonication is one of the promising approaches to disperse nanoparticles into the base material thoroughly. Furthermore, coupling treatments for MWNTs and polymer matrix also contribute to homogenous dispersion of MWNTs among polymer matrix. In this paper, MWNTs and KH-550 were dispersed with acetone via sonication method, then, the MWNTs/low density polyethylene (LDPE) composites was prepared by using melt blending process. Effects of MWNTs and LDPE coupling treatment on dispersion and electrical property of the MWNTs/LDPE nanocomposites were investigated. SEM observation on fracture surfaces of the nanocomposites explained the functions of sonication and coupling treatment on the dispersion, and electrical conductivity of the nanocomposites was measured by four-contact scheme. The results displayed that the optimum sonication temperature was 70 °C and the optimum sonication amount of MWNTs particles in 200 ml KH-550 acetone solution was 20 g. Moreover, dispersion of the nanocomposites was improved with increasing sonication power amplitude. Furthermore, dispersion and electrical conductivity of the nanocomposites with coupling treatment LDPE were better than those of the nanocomposites with uncoupling treatment LDPE. The good dispersion and electrical conductivity enhancement are based on the strong bonding and coupling reaction of MWNTs and LDPE matrix, which associated greatly with sonication and coupling treatment.     

Fatigue and Izod impact performance of carbon plain weave textile reinforced epoxy modified with cellulose microfibrils and rubber nanoparticles

This work details an experimental investigation on understanding the effects of hybrid epoxy resins, filled with micro-fibrillated cellulose (MFC) and carboxylated nitrile-butadiene rubber nanoparticles (XNBR), on the tensile–tensile fatigue performance of carbon plain weave textile reinforced composites. Twelve combinations of MFC and XNBR weight contents in the epoxy resin (from 0% to 0.5% MFC and from 0% to 3% XNBR) were considered for preliminary quasi-static tests and five of them were selected to study the fatigue behaviour considering different loading levels. Moreover, the effect of the twelve fillers contents was observed on the Izod impact strength. The investigation finds that the best fatigue performance, for the considered weight contents of fillers, is of the composite enhanced with the maximum content of MFC. The SEM observations of the fracture surfaces indicate the extensive “plastic” deformation of the matrix and the improved fibre and matrix adhesion.     

Aminofunctional silane layers for improved copper–polymer interface adhesion

The aim of this study was to characterize two different copper grades, oxygen-free copper, and phosphorous deoxidized copper, with aminofunctional silane layers on them and to study these silane layers as coupling agents in the injection-molded thermoplastic urethane–copper hybrids. The copper surfaces were as-received and modified, i.e., polished and oxidized. The copper surfaces and silane layers which were grown from solution concentrations of 0.25 and 0.5 vol% were studied with reflection absorption infrared spectroscopy (RAIRS), atomic force microscope (AFM), scanning electron microscope (SEM), and transmission electron microscope (TEM). The adhesive strengths of the copper–polymer joints were measured with peel tests and peeled surfaces were further studied with RAIRS, AFM, and FESEM. On the as-received copper surface, the silane layer was irregular and existed mainly in the surface roughness sites. This was the reason why hybrids manufactured with the as-received copper failed mostly in the silane layer. Hybrids manufactured with the oxidized copper sheets had a uniform silane layer and the hybrids failed mostly cohesively in thermoplastic urethane and had excellent peel strength values. In all silane-treated copper samples, Si–O–Si groups were formed confirming the cross-linking in the silane layer.     

Transcrystallization with reorientation in drawn PET/PA12 blend as revealed by WAXS from synchrotron radiation

Studying the isotropisation kinetics during melting of a drawn poly(ethylene terephthalate) (PET)/polyamide 12 (PA12) blend (60/40 wt %) at T_m ^PA12 < T_a < T_m ^PET by means of wide-angle X-ray scattering (WAXS) from synchrotron radiation a transcrystallization behaviour of PA12 was observed. It was also found that the nonisothermal transcrystallization behaviour of PA12 taking place during cooling down of the molten PA12 is characterized by reorientation of PA12 chain axis by 90° with respect of PET chains axis and of the starting chains axis direction as concluded from the WAXS patterns. A conclusion is drawn that PET microfibrils are not only effective nuclei for transcrystallization of the matrix but they cause a drastic reorientation of the matrix chains placing them perpendicular to the initial common for both PET and PA12 orientation direction.     

Formation of novel thermoplastic composites using bicomponent nonwovens as a precursor

This study focuses on a novel technique to produce thermoplastic composites directly from bicomponent nonwovens without using any resins or binders. Conceptually, the structure of the bicomponent fibers making up these nonwovens already mimics the fiber–matrix structure of fiber reinforced composites. Using this approach, we successfully produced isotropic thermoplastic composites with polymer combinations of polyethylene terephthalate/polyethylene (PET/PE), polyamide-6/polyethylene (PA6/PE), polyamide-6/polypropylene (PA6/PP), and PP/PE. The effects of processing temperature, fiber volume fraction, and thickness of the preform on the formation and structure of the nonwoven composites were discussed. Processing temperatures of 130 and 165 °C for PE and PP matrices, respectively, resulted in intact composite structures with fewer defects, for fiber volume fraction values of up to 51%. Moreover, an insight into the changes on the fine structure of the bicomponent fibers after processing was provided to better explain the mechanics behind the process. It is hypothesized that the composite fabrication process can result in annealing and increases the degree of crystallinity and melting temperature of polymers by thickening lamellae and/or removing imperfections. One of the other outcomes of this study is to establish what combination of mechanical properties (tensile and impact) nonwoven composites can offer. Our results showed that compared to glass mat reinforced thermoplastic composites, these novel isotropic nonwoven composites offer high specific strength (97 MPa/g cm⁻³ for PA6/PE), very high strain to failure (152% for PP/PE), and superior impact strength (147 kJ/m² for PA6/PP) which can be desirable in many critical applications.     

Melting Temperature and Change of Lamellar Thickness with Time for Bulk Polyethylene

The melting temperature of linear polyethylene has been obtained as a function of the time and temperature of crystallization. Recrystallization was minimized by a special melting procedure. By interpreting the melting points as characteristic of a given lamellar thickness, it was found that the thickness of crystals of appreciable age increased linearly with the logarithm of their time of existence. The lowest melting (i.e., thinnest) lamellae in a given specimen may be assumed to have either existed for only a short period of time, or to have been impeded in their growth in the chain direction, and they were found to have an estimated thickness close to that predicted by recent kinetic theories of polymer crystal growth with chain folding.     

玻璃长纤维增强树脂基复合材料的单轴时间相关棘轮行为实验研究

对玻璃长纤维增强树脂基复合材料(玻璃纤维体积分数为40%、50%)的室温单轴时间相关棘轮行为进行了较系统的单轴应力循环实验研究,讨论了该类复合材料在不同循环加载条件下的棘轮变形特征。结果表明：该类复合材料在非对称应力循环下将产生一定的棘轮变形,棘轮应变值随外加的应力幅值和平均应力的增加而增加;玻璃长纤维的引入使复合材料抵抗棘轮变形的能力明显强于未增强树脂基体材料,复合材料的棘轮变形量随玻璃长纤维含量的升高而下降;在室温下,复合材料的棘轮行为也具有明显的时间相关特性,棘轮应变值依赖于应力加载速率和峰值保持时间,随应力加载速率的下降和峰值保持时间的增加明显增加。     

EVA-g-PU/SBR/OMMT复合材料的制备与性能表征

采用熔融共混与熔融插层相结合的方法,制备了EVA-g-PU/SBR/OMMT复合材料.采用x-射线衍射仪(XRD)与透射电镜(TEM)研究了蒙脱土在聚合物基体中的分散状态,用电子万能试验机、摩擦磨损试验机测试了材料的力学性能及耐摩擦磨损性能,并通过扫面电镜分析了材料的磨损机理.结果表明,蒙脱土主要以插层型分布在聚合物基...