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.     

On the post-mortem fracture surface morphology of short fiber reinforced thermoplastics

The fracture surface morphology of short fiber reinforced thermoplastics (SFRTs) has often been used to assess qualitatively the degree of fiber–matrix interfacial adhesion. Mechanical properties such as tensile strength, fracture toughness and failure strain, etc. are then correlated with the morphology. Fracture surfaces showing fibers surrounded by a large amount of matrix material is commonly regarded as indication of strong fiber–matrix interfacial adhesion while smooth fibers are characteristic of weak interfacial adhesion. Many experimental results of SFRTs have been so interpreted. However, it is shown in this paper that strictly speaking, such interpretations are generally incorrect. Moreover, the amount of matrix material does not provide a quantitative measure of the adhesion. Correct implication of the morphology of fracture surfaces is clarified. Short glass fiber reinforced polyamide 6,6/polypropylene (PA 6,6/PP) blends toughened by rubber are employed as examples for SFRTs since the PA 6,6/PP blend system by changing PA 6,6 concentration in the matrix blend represents a wide range of matrix materials. It is demonstrated that the fracture surface morphology of such composites is dependent on both fiber–matrix interfacial adhesion strength and matrix shear yield strength. Consequently, tensile failure strain is well correlated with the post-mortem fracture surface morphology of these SFRTs.     

Web fabrication and characterization of unique winged shaped,area-enhanced fibers via a bicomponent spunbond process

High surface area fibers are sought after for a variety of applications such as liquid and air filtrations, medical and biopharmaceutical applications. Typically, higher specific surface area is achieved by resorting to using smaller fibers. This paper focuses on the development of a new shaped bicomponent spunbond structure for achieving high surface area. The fibers used in the spunbond process comprise a sacrificial sheath polymer and the shaped core polymer. Nonwovens were directly produced by using these fibers in a spunbond process. The spunbond webs were mechanically bonded by high energy water-jets and subsequently, the sheath polymer was removed in a 6 wt% NaOH solution at 90 °C. The final fibers showed a unique cross-sectional shape having 32 flaps or wings held together with a reasonable backbone. We report the results for a variety of polymer combinations including PP, PET, PBT, and PLA as the core and PLA and EastONE^TM as the sheath. The fiber morphologies were observed by SEM and showed 7–12 micron of the minor and 12–21 microns of the major with various core polymers used. The surface area of these fibers was compared to those of other shaped fibers.     

界面粘结对PET／尼龙66共混物结晶行为和力学性能的影响

利用ＳＥＭ、ＤＳＣ等方法，比较了尼龙６和尼龙６６对ＰＥＴ结晶的异相成核作用，研究了界面粘结状况对ＰＥＴ／尼龙６６共混物结晶行为及力学性能的影响。结果表明，尼龙６６对ＰＥＴ结晶的成核能力优于尼龙６。虽然界面粘结听改善不利于ＰＥＴ／尼龙６６共混物的结晶，但是经明显提高了共混物的力学性能。     

Carbon nanofibers prepared by a novel co-extrusion and melt-spinning of phenol formaldehyde-based core/sheath polymer blends

A novel route based on the solvent-free core/sheath melt-spinning of polypropylene/(phenol formaldehyde–polyethylene) [PP/(PF–PE)] to prepare the carbon nanofiber (CNF) has been demonstrated in this study. The approach consists of three main steps: co-extrusion of PP (core) and a polymer blend of PF and PE (sheath), followed by melt-spinning, to form the core/sheath fiber, stabilization of core/sheath fiber to form the carbon fiber precursor, and carbonization of carbon fiber precursor to form the final CNF. Both scanning electron microscopy and transmission electron microscopy images reveal long and winding CNF with diameter 100–600 nm and length greater than 80 μm. With a yield of ~45% based on its raw material PF, the CNF exhibits regularly oriented bundles which curl up to become rolls of wavy long fibers with clean and smooth surface. Results from X-ray diffractometry, Raman spectroscopy, and selected area electron diffraction pattern further reveal that the CNF exhibits a mixed-phase carbon material with graphitic particles embedded homogeneously in an amorphous carbon matrix.     

再生PET纤维/PP复合材料的结构及力学性能

为满足环境保护和可持续发展的需要,废弃无纺布的回收再利用已经成为材料领域的又一研究热点。本文以废弃无纺布为研究对象制得再生聚对苯二甲酸乙二醇酯(PET)纤维,通过热压成型技术制备不同纤维含量的PET/聚丙烯(PP)复合材料。综合利用SEM、DSC、XRD、拉伸性能测试等手段对PET/PP复合材料的结构和性能进行了研究。结果表明:低含量的PET纤维均匀分散在PP基体中,与基体间界面结合紧密;PET纤维的异相成核作用促进了PP分子链的结晶,提高了结晶度,使晶粒细化;这些微结构的变化有利于PET/PP复合膜力学性能的提高,当PET纤维含量仅为0.1%时,PET/PP复合膜的拉伸强度提高了25.99%,断裂韧性提高了61.96%。     

Manufacturing and physical properties of all-polyamide composites

Based on the difference in melting points between polyamide 66 (PA66) fiber and polyamide 6 (PA6) matrix, all-polyamide composites were fabricated under various processing conditions. In these all-polyamide composites, the reinforcement and matrix share the same molecular structure unit (–CONH–(CH₂)₅–). Because of the chemical similarity of the two components, good bonding at the fiber/matrix interface could be expected. Effects of processing temperature and cooling rate on the structure and physical properties of composites were investigated by SEM, DMA, DSC analyses, and static tensile test. Fiber/matrix interface strength benefited from elevated processing temperature. The static tensile results showed that the maximum of tensile strength was observed in the processing temperature range of 225–245 °C. At different cooling rates, crystallization temperature of PA6 in the composites was increased compared to the pure PA6 because of the nucleation effect of PA66 fiber surface to the PA6 matrix. A study of the matrix microstructure in a single fiber-polymer composite gave proof of the transcrystalline growth at the fiber–matrix interface, the reason behind which was the similar chemical compositions and lattice structures between PA6 and PA66.     

具有高界面压应力的高分子共混物Ⅰ.制备和拉伸性能

考察了高界面压应力对不相容聚对苯二甲酸乙二醇酯(PET)/聚乙烯(PE)和聚碳酸酯(PC)/PE共混物拉伸性能的影响.高界面压应力是共混物低温成型(PE的成型温度)时,分散相与基体从加工温度冷却到室温过程中基体的收缩比分散相粒子大产生的.尽管PET/PE和PC/PE共混物极不相容,但拉伸强度和模量随着PET和PC含量增加而增加.PET与PC含量相同时,PC/PE的拉伸强度和模量高于PET/PE的.采用Takayanangi方程计算共混物的拉伸模量时,具有高界面压应力的PC/PE共混物的拉伸强度高于界面有良好粘结的共混物的理论值,表明在不添加增容剂时,可通过控制加工条件改善共混物界面相互作用,提高共混材料的性能.     

纳米CaCO_3/PET短纤维/聚丙烯复合材料的制备及性能

制备了纳米CaCO3/聚丙烯、聚对苯二甲酸乙二酯(PET)短纤维/聚丙烯、CaCO3/PET短纤维/聚丙烯复合材料。分别测试了复合材料的力学性能,结果发现,与纳米CaCO3/聚丙烯、PET短纤维/聚丙烯两相复合材料相比,三相复合材料的力学性能尤其是冲击性能有明显的提高。采用X射线衍射(XRD)、动态力学分析(DMA)、电子扫描(SEM)系统研究了复合材料的增强机理,结果发现,在三相复合材料中,纳米CaCO3的加入明显提高了PET短纤维与聚丙烯基体界面之间的作用力和相容性,同时纳米CaCO3与PET短纤维的协同效应诱导了聚丙烯β晶的生成。     

In—situ Composite Based on Poly （ethylene terephthalate）,Polyamide and Polyethylene with Microfibres Formed through Extrusion and Hot Stretching

In-situ composites based on dispersed poly (ethylene terephthalate) (PET) or polyamide (PA),and continuous Polyethylene (PE) were prepared through a single screw extruder of Haake rheometer system with a rod-die relatively small in diameter.The extrudate was drawn at a drawing ratio of 3.1,and then quickly cooled in cold water.The specimens were obtained by injection molding at processing temperatures less than 190℃，far below the melting temperature of PET (265℃) and PA (230℃),which can maintain the solid state of PET and PA microfiber phase in the composites.Morphological observation with scanning electron microscopy (SEM) indicated that PET and PA can more or less form in-situ microfibers at compositions studied (0-20 wt pct PET or PA),and especially,PET and PA were almost deformed into fibers at the concentration of 15wt pct.Eensile strength and especially.PET and PA were almost deformed into fibers at the concentration of 15wt pct.Tensile strength and modulus of the blends reinforced by PET or PA microfibers showed to be increased from the tensile test results.The most noticeable improvement of the tensile properties occurred at 15wt pct of PET in PET/PE system,corresponding to the highest microfiber content,where the tensile strength reached 32.5 MPa,whereas only 19.5 MPa for the pure PE.     

The Influence of High Pressure Treatment and Thermal Pasteurization on the Surface of Polymeric Packaging Films

Several common single layer films (PE‐HD, PE‐LD, PP‐BO, PA6‐BO and PET‐BO) and multilayer (PS/PE, PP‐BO/PEpeel and PET‐BO/PE) films were treated by either high pressure (600 MPa) or temperature (80 °C/90 °C) to simulate a high pressure or thermal pasteurization process. The samples were tested by atomic force microscopy (AFM), profile method and surface energy measurements to obtain information about the influence of the treatments on the surface topography and surface energy of the samples and by differential scanning calorimetry and by tensile testing concerning material properties. As key figures arithmetic surface roughness (by AFM at Pulsed Force Mode and profile method), surface energy by surface energy measurement and adhesion between tip and surface by AFM were extracted. Results indicate an influence of both high‐pressure processing and thermal‐processing on the surface roughness of biaxial oriented polymer films as single layer films. Laminated biaxially oriented polymer films showed no changes regardless of which processing was performed. The surface energy was hardly affected by both of the treatments for any stretched, non‐stretched, single or laminated films.     

Polyamide single polymer composites prepared via in situ anionic polymerization of ε-caprolactam

In order to prepare the polyamide single polymer composites (SPC_PA) comprised of polyamide 6 (PA6) fiber and PA6 matrix, a novel method based on the in situ anionic polymerization of ε-caprolactam was developed. The influence of a critical process parameter, molding temperature, on the structure of SPC_PA was investigated by thermogravimetric analysis (TGA) and scanning electron microscope (SEM). Mechanical properties of SPC_PA prepared at 140, 160, 180, and 200 °C were appraised by three-point bending and tensile test. An optimum molding temperature (160 °C) at which both the tensile and flexural strength reached a peak value was found in the studied molding temperature range. High reaction degree (>93%), low void fraction (<2.5%) and strong and stable fiber/matrix interface contributed to the obvious reinforcing effect of PA6 fibers on PA6 matrix.     

热处理对碳纤维/聚酰胺6复合材料界面结晶及力学性能的影响

探究了热处理对聚酰胺6（PA6）在碳纤维（CF）表面的结晶行为及其界面力学性能的影响。利用差示扫描量热法（DSC）、偏光显微镜（POM）观察法等分析手段考察了热处理对PA6在CF表面结晶行为的影响,揭示了在热处理过程中,PA6进行链段重排,形成小且不完善的新结晶,导致结晶度的上升以及界面横晶形貌的完善;进一步通过单丝微球脱粘实验和单向CF/PA6复合材料横向拉伸实验考察了热处理对PA6与CF的界面结合性能的影响,揭示了经退火热处理的试样由于弱界面和应力集中的减少使界面剪切强度增加且单位体积断裂能下降。     

Effect of high‐pressure processing on the mechanical and barrier properties of selected packagings

This investigation focuses on the effect of high‐pressure processing (HPP) on possible changes of the mechanical properties and of the water vapour permeability of seven selected packaging materials. NOD 259 (PA‐PE), BB4L (Cryovac‐Grace packaging), PET/BOA/PE, PET/PVDC/PE, PA/SY, LDPE and EVA/PE were investigated (PET, polyester; PE, polyethylene; SY, surlyn; LDPE, low‐density polyethylene; EVA, polyethylene–vinyl acetate co‐polymer; BOA, biaxially oriented polyamide). These packaging materials were selected because of their interest to the food industry. All had an internal film of PE for food use. High‐pressure tests were realized at 10°C for 10 min at pressures of 200, 400 and 600 MPa, with water as a food‐simulating fluid. The depressurization rate was either rapid (pressure drop in <10s) or slow (20 MPa/min). Permeability to water vapour was realized using the NFF H 00 030–ASTM E96‐90 standard. Mechanical tests were carried out with a tensile testing machine (Lloyd LR5K), according to the NF 54‐102 standard. Maximal stress, rupture stress and strain at rupture were evaluated with non‐treated and treated samples. Obtained results showed that HPP minimally affects the mechanical strength of packaging material. The depressurization rate did not have any significant influence in our conditions. The barrier properties to water vapour were not significantly affected and were even slightly enhanced for LDPE, which is a packaging material commonly used for HPP applications and at least as a food contact material. Copyright © 2006 John Wiley & Sons, Ltd.     

Mechanical behavior of carbon fiber reinforced polyamide composites

The purpose of this work is to compare tensile, compressive and interlaminar shear properties of different carbon reinforcement/polyamide composites obtained by interfacial polymerization and hot compression molding techniques. Two types of composite matrices were studied: polyamide 6 and polyamide 6/6, both reinforced by fabric and unidirectional carbon fibers. The effects of the fiber volume fraction and the matrix on mechanical properties were analyzed through tensile, interlaminar shear and compressive tests. In general, the results have shown a slight increase of the composite elastic modulus, tensile and compressive strength with the increase of carbon fiber content. The microscopic damage development within selected composites during the loading has been observed through optical and scanning electron microscope techniques and has shown that shear failure at the fiber/matrix interface has been mostly responsible for damage development, initiated at relatively low stress.     

Chemical,morphological, and mechanical analysis of rice husk/post-consumer polyethylene composites

Composites were obtained from post-consumer high-density polyethylene (PE) reinforced with different concentrations of rice husk. PE and rice husk were chemically modified to improve their compatibility in composite preparation. Rice husk was mercerized with a NaOH solution and acetylated. The chemically modified fibers were characterized by FTIR and ¹³C NMR spectroscopy. The composites were prepared by extrusion of modified and unmodified materials containing either 5 or 10 wt.% fibers. The morphology of the obtained materials was analyzed by SEM. The chemical modification of the fiber surface was found to improve its adhesion with matrix. Flexural and impact tests demonstrated that PE/rice husk composites present improved mechanical performance comparatively to the pure polymer matrix, on the contrary no benefit is observed in the tensile strength over the pure PE.     

Toughening of polyamide 6 with β-nucleated thermoplastic vulcanizates based on polypropylene/ethylene–propylene–diene rubber grafted with maleic anhydride blends

The toughening of polyamide 6 (PA 6) with β-nucleated thermoplastic vulcanizates (TPVs) based on polypropylene (PP)/ethylene–propylene–diene rubber grafted with maleic anhydride (EPDM-g-MAH) blends was studied. A series of TPVs without and with different dosage of β-nucleating agent (β-NA) were prepared and used to toughen PA 6 at the same proportion. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) measurements showed that β crystals of PP were effectively induced in the TPVs. The PA 6 blends toughened with β-nucleated TPVs (β-TPVs) exhibit significantly enhanced toughness, balanced mechanical properties and thermal properties compared with PA 6 toughened by TPV without β-NA or only by EPDM-g-MAH. Phase morphologies of the blends characterized by scanning electron microscopy (SEM) showed that better interfacial adhesion caused by the migration of β-NA from PP to PA 6/PP interface and PP/EPDM-g-MAH interface gives rise to more uniform dispersion and smaller size of the dispersed phase; moreover, the core–shell structure comprised of rubber particles enveloped by PP on the surface, brings about easier and stronger interference of the stress field of EPDM phase.     

Filament winding of bicomponent fibers consisting of polypropylene and a liquid crystalline polymer

This paper is concerned with novel wholly thermoplastic composite materials suitable for use in filament winding. Bicomponent fibers consisting of a sheath of polypropylene (PP) of lower melting point and a core of a thermotropic liquid crystalline polymer (TLCP) of higher melting point were produced in a ratio of 30/70(w/w) using a modification of a standard bicomponent spinning process. The modifications were required to handle the necessity of melting the TLCP at a temperature in the range of 320°C while not raising the temperature of PP above 300°C which would lead to significant degradation of PP. The tensile modulus and strength of the fibers were 38.7 GPa and 465 MPa, respectively. A methodology was developed for establishing the conditions for filament winding these bicomponent composite fibers, which would allow adequate consolidation without disrupting the molecular orientation within the TLCP component and hence reinforcing properties. Cylinders and rings were generated with winding angles of 90 and 80°C under conditions in which the PP was melted but the TLCP retained its properties. The degree of consolidation was evaluated using the interlaminar shear strength test and optical microscopy. Because of the uniform distribution of the reinforcing component there was no failure observed in this test. The void content was determined to be 5.2%. The tubes generated from these materials have the potential for transport liquid oxygen and corrosive fluids.     

Effect of phenoxy-based coating resin for reinforcing pitch carbon fibers on the interlaminar shear strength of PA6 composites

Carbon fiber-reinforced thermoplastic composites have not been considered as constituent materials for structural parts due to the poor interfacial adhesion between the fiber and the thermoplastic matrix. In this work, polyamide 6 (PA6) composites with pitch carbon fibers (pCF) were fabricated by alternatively stacking PA6 films and pCF fabrics followed by being pressed. In order to improve the interfacial adhesion, phenoxy resin-based materials were coated on the surface of the fiber. The surface analyses of the fiber were carried out by XPS, TGA and dynamic contact angle method. Interlaminar shear strength (ILSS) of the composites was measured to evaluate the effect of the coating materials. The results showed that the composites with the coated pCF had higher ILSS than that with neat pCF by more than 20%. This indicated that a proper coating material can improve mechanical properties of the PA6 composites, which can be applied to the structural parts.     

Mechanical and fracture properties of ternary PE/PA6/GF composites

This article studies the mechanical properties of short fiber reinforced polymer blends comprised of a soft thermoplastic matrix (polyethylene, PE), a rigid dispersed thermoplastic phase (polyamide-6, PA6) and glass fiber reinforcement. These ternary composites are designed as a model system to investigate the impact of the mutual interactions of the three phases on the composite mechanical properties. For this purpose two types of fibers are used, dispersed-phase and matrix-phase compatible fibers, respectively.