Influence of chemical treatments on cellulose fibers for use as reinforcements in poly(ethylene‐co‐vinyl acetate) composites

This work evaluates different chemical treatments on cellulose fibers as reinforcement agents in poly(ethylene‐vinyl acetate) (EVA) composites. The cellulose fibers were prepared with three chemical modifications using triethoxyvinylsilane, acetic anhydride (AA), and glycidyl methacrylate (GMA). Composites were prepared with 10 phr of cellulose fibers by means of extrusion and hot press conformation. The fiber treatment levels were successfully demonstrated through Fourier transform infrared spectroscopy with the appearance of characteristic bands in each chemical group, and scanning electron micrographs showed altered textures on the surfaces, polymerized material and fiber agglomerations after the chemical treatments that were most evident in the AA and GMA treatments. The composites reinforced with treated fibers showed improvement in their mechanical properties at the yield points and were reduced in deformation. When activated with dicumyl peroxide, the mechanical properties were even more improved and the interface regions exhibited better interactions between the cellulose fibers and the EVA matrix. POLYM. COMPOS., 37:1991–2000, 2016. © 2015 Society of Plastics Engineers     

Morphology and properties of melt-spun polycarbonate fibers containing single- and multi-wall carbon nanotubes

Polycarbonate fibers based single wall and multi-wall nanotubes (SWNT and MWNT) were prepared by first dispersing the nanotubes via solvent blending and/or melt extrusion followed by melt spinning the composites to facilitate nanotube alignment along the fiber axis. Morphological studies involving polarized Raman spectroscopy and wide angle X-ray scattering using a synchrotron radiation source show that reasonable levels of nanotube alignment are achievable. Detailed transmission electron microscopy (TEM) investigations on the polymer-extracted composite fibers reveal that MWNT more readily disperse within the PC matrix and have higher aspect ratios than do SWNT; extraction of the polymer from the composite prior to TEM imaging helps overcome the common issue of poor atomic contrast between the CNT and the organic matrix. Stress-strain analysis on the composites fibers show that MWNT, in general, provide greater stiffness and strength than those based on SWNT. Despite significant reinforcement of the polycarbonate, the level of reinforcement is far below what could be achieved if the nanotubes were completely dispersed and aligned along the fiber axis as predicted by composite theory.     

Preparation and characterization of poly (vinyl butyral)‐leather fiber composites

This study reports the preparation and characterization of composites with recycled poly (vinyl butyral) (PVB) and wet blue leather fiber with leather contents of 30, 50, and 70 wt%, using an extruder equipped with a Maillefer single screw operated with a flat extrusion die. The components of the composites were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and Fourier transform infrared spectroscopy (FTIR). After extrusion, the PVB/leather composite plates were compression‐molded to obtain specimens for testing the tensile properties, hardness, abrasion resistance, and tear strength. The morphologies of the composites were analyzed by scanning electron microscopy (SEM). The DMA and FTIR analyses showed that the recycled PVB contained plasticizer remained in the polymer matrix after extrusion. The SEM analysis revealed good interfacial adhesion between the PVB matrix and the leather fibers. Increasing the leather content in the composites led to a significant increase in the tensile modulus and a reduction in the tensile strain at breaks. The Shore hardness of the composites increased with the wt% of leather, whereas the abrasion resistance decreased. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers.     

Study of the Processing and Mechanical Properties of In Situ Composite Materials of Thermoplastics with Thermotropic Liquid Crystalline Polymers

By blending thermoplastics (TPs)—polycarbonate (PC) and polyethersulfone (PES)—with thermotropic liquid crystalline polymers (TLCPs)—KU9221 and KU9231—and then extruding the blends to form fibers, the in situ reinforcing characteristics were studied. The injection experiment of blends was compared with the extrusion experiment. According to the experimental results, in situ reinforcing characteristics of these processes were analyzed theoretically. These researches have come to some important conclusions. TLCP domains can be transformed to form fibers that are oriented in the direction of flow during processing; these TLCP microfibers result in improved mechanical properties of the TP/TLCP blends. The extruding flow is more effective in orienting TLCP domains and results in better in situ reinforcement than that of injection molding, and the extruded fibers have better mechanical properties. The mechanical properties of the blend fibers are improved greatly with increasing tensile ratio of melt drawing and the content of TLCPs.     

Effects of the coagulation temperature on the properties of wet‐spun poly(vinyl alcohol)–graphene oxide fibers

Graphene oxide (GO) as a positive reinforcement filler was dispersed into a poly(vinyl alcohol) (PVA) dope and wet‐spun into composite fibers. The effects of two EtOH coagulation baths maintained at ?5 and 25 °C, respectively, on the morphology, structure, and mechanical properties of the composite fibers were investigated. The results show that gel spinning at ?5 °C led to a relatively large shrinkage ratio, thin diameter, and low porosity of the as‐spun fibers. Simultaneously, the low coagulation temperature also greatly contributed to the formation and preservation of the liquid‐crystalline phase of the GO sheets and interrupted the crystalline zone of PVA less. As a result, either the tenacity or the elongation at break of the fibers spun at ?5 °C was higher than those of the fibers spun through a coagulation bath at 25 °C. In particular, 1 wt % GO showed the highest reinforcement effects among all of the wet‐spun composite fibers. Hence, controlling the gelling–demixing process at a low temperature will provide more instructive insights for tailoring functional industrial textiles with excellent mechanical properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45463.     

Optimized Preparation Techniques for PVC–Green Coconut Fiber Composites

Composites of poly(vinyl chloride) (PVC) and green coconut fibers were prepared by two techniques: dry blending + extrusion and dry blending + mixing. The degree of homogeneity of the mixes was evaluated through dynamic modulus measurements in both the molten and the solid states. Dry blending + mixing was found to be most appropriate in the preparation of laboratory scale composites. In addition, results suggest that no physico-chemical interactions occur between the matrix and the fibers.     

Processing of reinforced plastics using multi-screw compounders

Polymer modification by addition of reinforcing agents represents a popular means of increasing physical property values. The polymer matrix has been forced to accept up to 55 percent by weight of fibrous reinforcement and 80 percent by weight of powdered types in order to meet application requirements. These materials demand sophisticated mixing equipment which must provide extensive intake and conveying capabilities, polymer wetting of reinforcement, and dispersion of reinforcement. This process must also be conducted with controlled shear intensity and excellent temperature and residence time control in order to respect polymer thermal sensitivity and product requirements. The extrusion process is a proven economical method for incorporating reinforcements into polymer resins. Co-rotating intermeshing twin-screw extruders are particularly suited for these tasks. Positive conveying, self-wiping, and shear intensive mixing characteristics provided by the screw mechanism satisfy requirements of reinforcement compounding. This mechanism allows interruption of streamline flow which is needed to disperse both high and low aspect ratio reinforcing agents into a polymer matrix. Mathematical representation of the benefits of twin-screw extrusion (relative to single-screw) related to pumping and mixing capability have been developed based on the classical pressure flow continuity equation with proper selection of boundary conditions.     

Rheology of molten blends of polyoxymethylene and ethylene-vinyl acetate copolymer and the microstructure of extrudates as a function of their melt viscosities

Blends of polyoxymethylene (POM) with a copolymer of ethylene and vinyl acetate (CEVAc) have been studied. The effect of viscosity ratio for melts of the components on the processes of fiber formation in extrudates and on the rheological properties of the molten blend has been tested. The viscosity ratio of the fiber-forming POM and the matrix varied in the range 0.35-27.7. POM ultrathin fibers of unlimited length can be formed in the CEVAc only at a viscosity ratio close to unity. For ratios much greater than unity, the extrudate is found to contain short fibers and a finely dispersed powder or no fibers at all. If the viscosity of the POM melt is lower than that of the matrix, films are formed in addition to fibers. The second factor that governs fiber formation is the extrusion shear stress. An optimum shear stress exists at which the amount of ultrathin fibers is a maximum.     

Modification of nylon-polyethylene blends via in situ fiber formation

Extrusion of nylon-PE films has resulted in the successful in situ formation of high aspect ratio (possibly continuous) nylon fibers as desired. However, these fibers surprisingly provide no significant reinforcement in uncompatibilized blends. While certain compatibilizing agents appear to give properties more characteristic of a fiber reinforced system, achieving higher levels of reinforcement (approaching those anticipated for fibers containing highly oriented molecules) is judged to be difficult using current methods. Based on analysis of yield stress versus modulus, the act of drawing films appears to have the greatest potential for improving reinforcement beyond the limiting case for unmodified polymers. However, the greatest challenge in realizing this potential lies in overcoming the limited extensibility allowed by nylon under normal conditions.     

超大长径比双螺杆挤出机制备聚丙烯腈初生纤维

采用自主研发的超大长径比(136)双螺杆挤出机实现了PAN初生纤维的纺丝制备,研究了PAN粉料质量分数(16%、20%、24%)、双螺杆挤出机机筒温度(50、60、70℃)、循环挤出次数(0、1、2)对PAN初生纤维力学性能及表面形貌的影响。结果表明,PAN初生纤维的拉伸强度随质量分数、机筒温度和循环挤出次数的增加而增大;PAN初生纤维的断裂伸长率随质量分数和循环挤出次数的增加而减小,随机筒温度的升高而增大;随着循环挤出次数增加,纤维表面越来越规整,缺陷逐渐减少。研究结果为利用超大长径比双螺杆挤出机制备出性能更好的PAN初生纤维奠定了基础。     

Polypropylene/poly(vinyl acetate) blend fiber

Polypropylene/poly(vinyl acetate) (PP/PVAc) (30/70) blend possesses higher thermal stability than PVAc and is stable below 300°C. The viscosity of the blend is lower than that of PP and PVAc at 220°C. The blend fibers have sheath-core morphology; the core is composed of PP fibrils because PP has reasonably higher viscosity than PVAc. Due to the reinforcement of PP fibrils, the tensile strength and modulus of the blend fibers were increased. The blend fibers drawn at 50°C possess better mechanical properties than those drawn at 90°C. © 1994 John Wiley & Sons, Inc.     

Antistatic‐reinforced biocomposites of polyamide‐6 and polyaniline‐coated curauá fibers prepared on a pilot plant scale

Curauá fibers were used with success as a reinforcing agent in polyamide‐6, however, for several applications, an antistatic dissipation property is also desirable and the incorporation of an intrinsically conducting polymer is a suitable way to promote this. The novelty of this work is the simultaneous introduction of these two properties, antistatic and reinforcement, using one filler, obtained by depositing polyaniline on the surface of short curauá fibers. Nearly 5–30 wt% of these modified fibers were dispersed by extrusion in polyamide‐6, the composites were injection molded and characterized by electrical, mechanical, morphological, and rheological properties. The tensile strength of the polyamide‐6 composites reinforced with 5 and 30 wt% of polyaniline coated curauá fibers, was 56% higher and 23% lower than the values obtained for pure polyamide‐6, respectively. Also, the composite reinforced with 5 wt% of fibers, when processed with lower shearing rates, showed conductivity in the range of antistatic materials, 4 μS cm⁻¹. Scanning electronic microscopy and infrared spectroscopy showed an improvement in interfacial adhesion in PA‐6/CF‐PAni composites. The composite prepared with 5 wt% of polyaniline coated curauá fibers gave the best balance between the electrical and the mechanical properties. Extrusion and injection molding methods used here are suitable for continuous large scale production. POLYM. COMPOS., 34:1081–1090, 2013. © 2013 Society of Plastics Engineers     

Morphological studies on extruded films and filaments of polypropylene

In the present work, an attempt has been made to study the development of morphology during extrusion and uniaxial stretching of polypropylene (PP) films and filaments at corresponding conditions. Dies for extrusion of films and filaments were designed to achieve similar extrusion velocity and shear rates. Orientation in films and fibers of PP produced from these dies was determined by birefringence and wide-angle X-ray diffraction (WAXD). The degree of crystallinity was determined by density and WAXD. The superstructure developed during extrusion was studied in films by small-angle light scattering. It was inferred that films and fibers prepared under similar conditions would produce similar morphology. Hence, films can be characterized by optical techniques when it is difficult to study fibers. © 1994 John Wiley & Sons, Inc.     

Melt spinning of silane–water cross-linked polyethylene–octene through a reactive extrusion process

The aim of this study is to produce silane–water cross-linked polyethylene–octene (PEO) fibers through a reactive extrusion process. First, PEO is silane-grafted during an extrusion process followed by a spinning step. Then, grafted PEO monofilaments are introduced in water-based solution to perform cross-linking. The influence of process parameters on bulk PEO cross-linking degree was first investigated through a mixture design methodology which revealed that the most influent parameters are extrusion temperature and time. Using these results and the response surface methodology, silane–water cross-linked PEO monofilaments could be produced with desired gel contents after proceeding to some adjustments of processing parameters. The influence of cross-linking degree and draw ratio on macroscopic properties of PEO monofilaments was investigated. In particular, the cross-linked PEO fibers thermomechanical stability increases with cross-linking degree up to 170 °C for cross-linking degrees higher than 55%. Moreover, cross-linked PEO fibers exhibit higher elastic properties than neat PEO fibers.     

Preparation and performance of braid‐reinforced poly(vinyl chloride) hollow fiber membranes

A novel braid‐reinforced (BR) poly(vinyl chloride) (PVC) hollow fiber membrane was fabricated via dry‐wet spinning process. The mixtures of PVC polymer solutions were uniformly coated on the tubular braid which contained polyester (PET) and polyacrylonitrile (PAN) fibers. The influences of braid composition on structure and performance of BR PVC hollow fiber membranes were investigated. The results showed that the prepared BR PVC hollow fiber membranes were composed of two layers which contained separation layer and tubular braid supported layer when the PET and PET/PAN hybrid tubular braids were used as the reinforcement. But the sandwich structure appeared when the PAN tubular braid was used as the reinforcement, which revealed outer separation layer, tubular braid supported layer and the inner polymer layer. The BR PVC hollow fiber membranes that prepared by PET/PAN hybrid tubular braid had favorable interfacial bonding state compared with the membrane prepared by pure PET or PAN tubular braid. The pure water flux of the BR PVC hollow fiber membranes that prepared by the PET/PAN hybrid tubular braid were lower than that prepared by pure PET or PAN tubular braid, but the rejection of Bovine serum albumin was opposite. The tensile strength of prepared BR PVC hollow fiber membrane was higher than 50 MPa. Both of the tensile strength and elongation at break decreased with the increase of the PAN filaments in the PET/PAN hybrid tubular braid. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45068.     

扭转挤出技术制备再生碳纤维增强聚苯乙烯化学发泡复合材料

采用再生碳纤维（RCF）作为增强体和成核剂及扭转挤出技术制备了聚苯乙烯（PS）/RCF为主体成分的硬质泡沫,利用三维（3D）层析成像技术、电子显微镜等对泡沫材料的微观结构、泡孔形态进行了研究。结果表明,在扭转挤出过程中,聚合物熔体产生了扭转螺旋流动,使纤维充分分散并沿流动方向取向;并且改善了整个体系的混合和温度性能,使得泡孔形态整体较为均匀;此外,泡沫质量受到机头温度的影响,且当机头温度高于180 ℃时,制品表面变得凹凸不平,气体发生逃逸现象;RCF的加入,会使气泡会沿着RCF取向方向生长,但是添加过多的RCF,会影响气泡成核。     

Properties of fibers produced from soy protein isolate by extrusion and wet-spinning

Fibers were produced from soy protein isolate by both wet-spinning and extrusion. In the wet-spinning process, aged, alkaline protein solution was forced through a spinnerette into an acid coagulating bath. In the extrusion process, a twinscrew extruder forced a protein isolate-water mixture through a die. The physical properties of the fibers were measured at various water activities. The fibers produced by both methods were brittle and lacked tensile strength (tenacity). The addition of glycerol reduced brittleness in extruded fibers. Zinc and calcium ions decreased the brittleness of wet-spun fibers. The tenacity of soy fibers was significantly improved by post-spinning treatments, including acetic anhydride, acetaldehyde, glyoxal, glutaraldehyde, a combination of glutaraldehyde and acetic anhydride, and stretching. The best extruded fibers were produced with a mixture of 45% soy protein, 15% glycerol, and 40% water, finished with a combination of glutaraldehyde and acetic anhydride and then stretched to 150% their original lengths. The best wet-spun fibers were produced with a 19.61% soy protein suspension at pH 12.1; coagulated in a 4% hydrochloric acid solution that contained 3.3% sodium chloride, 3.3% zinc chloride, and 3.3% calcium chloride; and followed by treatment with 25% glutaraldehyde and stretching to 170% their original lengths.     

Performance of fibers embedded in a cementitious matrix

Reinforcement of cementitious materials with short fibers has been proved to be an economical and effective way to convert these brittle materials to ductile products. Many fibers with different geometries have been used as reinforcement materials. Fibers bonding to cementitious materials play an important role in mechanical performance of these composites. This article describes the performance of (homemade) fibers as reinforcement in cement‐based materials by investigation on bonding characteristic of fiber to cement matrix. To this end, the fibers (glass, polypropylene, polyacrylonitrile (PAN), and high strength nylon 66 (N66)) are characterized using microscopy analysis, tensile strength, and alkali attack tests. The fibers embedded in the cement matrix, then, pulled‐out to evaluate their bonding to cementitious materials. SEM analysis is used to study fiber/cement interfacial transition zone. The results show that PAN fibers have the advantages of preparing for cementitious reinforcement. It was found that the reinforcing efficiency of fibers‐reinforced cementitious composites was strongly depending on interfacial contact area in fiber/matrix interface and chemical/physical properties of fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effect of carbon nanotube aspect ratio and loading on the elastic modulus of electrospun poly(vinyl alcohol)-carbon nanotube hybrid fibers

The reinforcement effect of carbon nanotubes (CNTs) has been examined as a function of their loading and aspect ratio in poly(vinyl alcohol) (PVA) based hybird fibers. Lignosulfonic acid sodium salt (LSA) was used to disperse CNTs to produce consistently high CNT loaded PVA-LSA-CNT hybrid fibers using an electrospinning process. The elastic modulus of individual fibers was measured using atomic force microscopy. The presence of CNTs significantly increased the average elastic modulus of PVA-LSA-CNT fibers compared to PVA-LSA fibers. The elastic modulus, however, exhibited no fiber diameter dependency. Transmission electron microscopy (TEM) was used to determine the loading and the aspect ratio of CNTs in each hybrid fiber. The CNT loading in PVA-LSA-CNT fibers varied widely due to non-uniform CNT dispersion and displayed no relationship with the elastic modulus. Our results also demonstrated that the average value of CNT aspect ratio significantly affected the elastic modulus of the hybrid fibers. Such a result was in agreement with theoretical prediction in which the stress transfer efficiency in a composite matrix is strongly dependent on the CNT aspect ratio.     

Mechanical properties of poly(vinyl chloride)/wood flour/glass fiber hybrid composites

Short glass fibers were added to poly(vinyl chloride) (PVC)/wood flour composites as reinforcement agents. Unnotched and notched impact strength of PVC/wood flour/glass fiber hybrid composites could be increased significantly without losing flexural properties by adding type L glass fibers and over 40% of PVC. There was no such improvement when using type S glass fiber. The impact strength of hybrid composites increased along with the increment of the type L glass fiber content at a 50% PVC content. At high PVC contents, impact fracture surfaces were characterized by wood particle, glass fiber breakage and pullout, whereas interfacial debonding was the dominant fracture mode at higher filler concentrations. The significant improvement in impact strength of hybrid composites was attributed to the formation of the three‐dimensional network glass fiber architecture between type L glass fibers and wood flour.