Natural fiber blend—nylon 6 composites

In this study, engineering thermoplastic composites were prepared from natural fiber blend–filled nylon 6. Natural fiber blend from a mixture of kenaf, flax, and hemp fibers were added to nylon 6 using melt mixing to produce compounded pellets. The natural fibers/ nylon6 composites with varying concentrations of natural fibers (from 5 to 20 wt%) were prepared by injection molding. The tensile and flexural properties of the nylon 6 composites were increased significantly with the addition of the natural fiber blend. The maximum strength and modulus of elasticity for the nylon 6 composites were achieved at a natural fiber blend weight fraction of 20%. The Izod impact strength of composites decreased with the incorporation of natural fibers without any surface treatments and coupling agent. The melt flow index (MFI) also decreased with increasing natural fiber blend loading. The results of tensile and flexural modulus of elasticity (FMOE) are in accordance with the rheological data from the MFI measurements. The increase in the tensile and flexural properties indicated that efficient bonding occurred between the natural fibers and nylon 6. No fiber pullout was observed during the scanning electron microscopic analysis of the fracture surfaces. The higher mechanical results with lower density demonstrate that a natural fiber blend can be used as a sufficient reinforcing material for low‐cost, eco‐friendly composites in the automotive industry and in other applications such as the building and construction industries, packaging, consumer products, etc.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

凯芙拉纤维/尼龙6热塑性复合材料的研制

研究了凯芙拉纤维与尼龙 6单体通过阴离子原位聚合制备热塑性复合材料的方法。以氢氧化钠为引发剂 ,甲苯二异氰酸酯 (TDI)为活化剂 ,确定体系的聚合温度为 160℃ ,引发剂、活化剂用量为6.42 m ol/L ,聚合时间 60 min,在此条件下聚合速度较快 ,单体转化率 1h后达 95 %以上。研究发现 ,凯芙拉纤维经酰化处理后 ,基本上不会对己内酰胺阴离子聚合体系产生阻聚作用     

Monitoring of nylon 6,6/carbon fiber composites processing by X‐ray diffraction and thermal analysis

This work reports a study made to obtain carbon fiber/nylon 6,6 prepreg composites by hot‐compression molding. Thermogravimetric analysis (TG) and crystallinity degree determination were carried out to monitor the nylon 6,6 behavior during the different steps of the composite processing. The homogeneity of the carbon fiber/polymer matrix distribution was verified using microscopic analyses and the fiber content was determined by the acid‐digestion method. The results show that the processing parameters employed were adequate, allowing the manufacture of laminates with good texture and an adequate reinforcement/matrix relation (60/40). However, improvements need be done to minimize the pullout effect observed in the tensile specimens. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3114–3119, 2002     

Properties of bio‐based polymer nylon 11 reinforced with short carbon fiber composites

In this work, micro‐composite materials were produced by incorporating 3‐mm long reclaimed short carbon fibers into bio‐based nylon 11 via melt compounding. A systematic fiber length distribution analysis was performed after the masterbatching, compounding and an injection moulding processes using optical microscopy images. It was found that the large majority of the fibers were within the 200–300 μm in length range after the injection moulding process. The mechanical (flexural and tensile), thermo‐mechanical, and creep properties of the injection moulded materials are reported. We found that an enhancement in flexural and Young's modulus of 25% and 14%, respectively, could be attained with 2 wt% carbon fiber loading whilst no significant drawback on the ductility and toughness of the matrix was observed. The creep resistance and recovery of the nylon 11, tested using dynamic mechanical thermal analysis at room temperature and 65°C, was significantly improved by up to 30% and 14%, respectively, after loading with carbon fiber. This work provides an insight into the property improvement of the bio‐based polymer nylon 11 using a small amount of a reclaimed engineered material. POLYM. COMPOS., 36:668–674, 2015. © 2014 Society of Plastics Engineers     

Conducting aluminum‐filled nylon 6 composites

This work is concerned with the preparation and characterization of composite materials prepared by compression molding of a mixture of aluminum flakes and nylon 6 powder. The electrical conductivity, density, hardness and morphology of composites were investigated. The electrical conductivity of the composites is < 10⁻¹¹ S/cm unless the metal content reached the percolation threshold, beyond which the conductivity increased markedly by as much as 10¹¹. The volume fraction of conductive filler at the percolation threshold was calculated from experimental data, by fits to functions predicted by the percolation theory. Decreasing the average particle diameter of filler leads to increased percolation threshold (it varies from 23 to 34 vol% for the three different fillers studied) and decreased maximal conductivity of composites. The density of the composites was measured and compared with values calculated assuming different void levels within the samples. Furthermore, it is shown that for certain sizes of particle filler, the hardness decreases initially with the increase of metal concentration, possibly because of poor surface contact with the nylon matrix, but, starting from a certain value, there is a hardness increase. For the smallest particle filler, the hardness of samples is not influenced by the presence of the filler.     

Shielding effectiveness density theory for carbon fiber/nylon 6,6 composites

We present a simple density theory based on first principles that predicts the shielding effectiveness of composite matrix materials at filler loadings near or above the percolation threshold. Such a model has practical applications in electromagnetic interference and radio frequency interference, and is validated here for Fortafil 243 carbon fiber within nylon 6,6. In brief, the theory predicts that the most important parameter on the shielding effectiveness of a sample is the carbon fiber volume percent. At very high filler loadings, experimental results show a weak dependence on the frequency of the wave to be shielded, which may be attributed to enhanced reflection from multiple, coherent scatterers (carbon fiber network). These effects are not considered in our model. Nevertheless, advantages of this model are ease of use and improved predictive capabilities when compared to models previously reported in the literature. Our model performs very well over an electrical resistivity range from 10¹⁵ ohm‐cm (at low filler loading levels below the percolation threshold) down to 10⁻¹ ohm‐cm (at high filler loading levels well above the percolation threshold), and can be used to determine filler loadings needed to provide a certain level of shielding of electromagnetic waves. POLYM. COMPOS. 26:671–678, 2005. © 2005 Society of Plastics Engineers     

废聚丙烯/废轮胎胶粉/废尼龙短纤维复合材料Ⅱ.工艺条件

采用反应挤出方法制备了废聚丙烯／废轮胎胶粉／废尼龙短纤维(WPP／GRT／WSF)复合材料,讨论了螺杆转速、机头温度对WPP／GRT／WSF复合材料力学性能的影响。结果表明,当螺杆转速为15r／min,机头温度为185～195℃时,WPP／GRT／WSF复合材料的力学性能达到最佳,拉伸强度为13．6MPa,冲击强度为25．2kJ／m^2。按照最佳配方和工艺挤出管材的拉伸强度为4,6MPa,冲击强度为5．4kJ／m^2,爆破压力为0．69MPa。     

Improvement of mechanical properties of composites through polyamide grafting onto kevlar fibers

Chemical modifications of the surface of Kevlar fiber were investigated as a means of improving fiber-matrix adhesion. The fiber surface was used as a polymerization support for interfacial polycondensation. Nylon-6,6 was successfully polymerized in this way. The grafted nylon was characterized by ESCA (electron spectroscopy for chemical analysis), DSC (differential scanning calorimetry), and extraction procedures. An increase of the transcrystalline layer thickness was observed through optical microscopy, indicating better fiber-matrix adhesion. Both plasma treated fibers having been submitted or not to chemical treatments were used as reinforcements for nylon-6,6 unidirectional composites. Improvement of the mechanical properties were related to better interfacial interactions due to grafted nylon chains.     

Shielding‐effectiveness modeling of carbon‐fiber/nylon‐6,6 composites

We have formulated a linear theory for the shielding effectiveness of composite matrix materials and have tested the theory for various amounts of ThermalGraph DKD X carbon fiber within nylon 6,6. The theory predicts that the most important parameters for the shielding effectiveness of a sample are the carbon‐fiber volume percentage and the frequency of the wave to be shielded. Although we expected the model to be valid at low filler‐loading levels, it actually performs remarkably, covering an electrical‐resistivity range of 10¹⁶ (at low filler‐loading levels) to 10¹ Ω cm (at high filler‐loading levels), well above the percolation threshold of electrical‐resistivity theory. The model performs much better than those reported in the literature and can be used to determine filler loadings needed to provide a certain level of shielding of electromagnetic waves. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 62–69, 2005     

Natural fiber eco‐composites

The natural fiber (NF) reinforced composites, so called eco‐composites, are subject of many scientific and research projects, as well as many commercial programs. The growing global environmental and social concern, high rate of depletion of petroleum resources, and new environmental regulations have forced the search for new composites and green materials, compatible with the environment. The aim of this article is to present a brief review of the most suitable and commonly used biodegradable polymer matrices and NF reinforcements in eco‐composites, as well as some of the already produced and commercialized NF eco‐composites. POLYM. COMPOS. 28:98–107, 2007. © 2007 Society of Plastics Engineers     

Conducting polymer composites of zinc‐filled nylon 6

The present work is concerned with the effect of processing variables and filler concentration on the electrical conductivity, hardness, and density of composite materials prepared by compression molding of a mixture of zinc powder and nylon 6 powder. The electrical conductivity of the composites is <10^?12 S/cm, unless the metal content reaches the percolation threshold at a volume fraction of about 0.18, beyond which the conductivity increases markedly by as much as 10 orders of magnitude. The density of the composites was measured and compared with values calculated by assuming different void levels within the samples. Furthermore, it is shown that the hardness increases with the increase of metal concentration, but for values of filler volume fraction higher than about 0.30 the hardness of samples remains almost constant. Two parameters of molding process, temperature and time, were shown to have a notable effect on the conductivity of composites, whereas pressure has no influence on this property in the pressure range considered. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1449–1454, 2001     

Characterization of mixed fiber nylon composites incorporating composite scrap

Recycling of engineering thermoplastics and their composites represents both a challenge and an opportunity in today's material science. A study on nylon 6,6 based composites with mixed glass-fiber and carbon-fiber reinforcement, including nylon composite scrap in their formulation, is reported. Several formulations were prepared by injection molding and were characterized by stress-strain-measurements, impact testing, simultaneous differential thermal analysis and thermogravimetry (DTA-TG), density measurements and scanning electron microscopy (SEM). No dependence on mechanical properties due to increasing amounts of scrap in the composites was found up to 10.4 wt%. The generated recycled composites generally showed lower mechanical properties as compared with the virgin composite because of a poor matrix-fiber adhesion.     

Studies in the properties of nylon 6–glass fiber composites

Caprolactam has been anionically polymerized within the planar-random continuous glass mat reinforcement using a technique similar to reaction injection molding and up to 55% (w/w) [i.e., 33% (v/v)] glass fiber loading was achieved. The fiber volume fraction distribution across the diameter of the composite was observed to be reasonably uniform. The tensile stress–strain properties were determined. Composite modulus and strength appeared to be linearly dependent on the fiber volume fraction and increase with fiber volume content. The type of composite material studied has been used for compression molding of articles. Therefore, some tensile data were redetermined after compression molding and possible changes in degree of crystallinity resulting from the change in the thermal history monitored by differential scanning calorimetry. A 50% drop in the percent degree of crystallinity (monoclinic modification) of the as-polymerized composite and a deterioration in the tensile properties of the composite were observed after compression molding. On compression molding the mold surface needs to be completely covered with the composite sheet material; otherwise, matrix polymer flows out of the composite, and areas deficient in reinforcement result.     

Wood‐fiber/high‐density‐polyethylene composites: Compounding process

The compounding process directly influenced the compounding quality of wood–polymer blends and finally affected the interfacial bonding strength and flexural modulus of the resultant composites. With 50 wt % wood fiber, the optimum compounding parameters for the wood‐fiber/high‐density‐polyethylene blends at 60 rpm were a temperature of 180°C and a mixing time of 10 min for the one‐step process with a rotor mixer. The optimum compounding conditions at 90 rpm were a temperature of 165°C and a mixing time of 10 min. Therefore, a short compounding time, appropriate mixing temperatures, and a moderate rotation speed improved the compounding quality of the modified blends and the dynamic mechanical properties of the resultant composites. The melt torque and blend temperature followed a polynomial relationship with the loading ratio of the wood fiber. The highest melt torque and blend temperature were obtained with 50% wood fiber. The coupling treatment was effective for improving the compatibility and adhesion at the interface. The two‐step process was better than the one‐step process because the coupling agents were more evenly distributed at the interface with the two‐step process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2570–2578, 2004     

E‐glass/DGEBA/m‐PDA single fiber composites: Interface debonding during fiber fracture

In this paper, we examine the regions of debonding between the fibers and the matrix surrounding fiber breaks formed during single fiber fragmentation tests. The fiber breaks are accompanied by areas of debonding between the matrix and the surface of the fiber. With increasing applied strain, the lengths of these debonded regions generally increase. At the end of the test, the matrix tensile strain adjacent to the debond regions is an order of magnitude higher than the applied strain (40% vs. 4%). Although the debond edges typically remain attached at the same locations on the fiber fragments, debond propagation along fiber fragments under increasing strain has been observed in some cases. The phenomenon is termed secondary debond growth, and two mechanisms that trigger secondary debond region growth have been proposed. As expected, tests with bare fibers and with fibers coated to alter interface adhesion indicate that the average size of debonded regions at the end of the test increases as the calculated interfacial shear strength decreases. However, a decrease in the “apparent” interfacial shear strength resulting from an increase in testing rate results in a decrease in the size of the average debond region. This result suggests an increase in the amount of energy stored in the matrix from the fiber fracture process. POLYM. COMPOS. 28:561–574, 2007. © 2007 Society of Plastics Engineers     

Preparation and properties of PBS/sisal‐fiber composites

We report the preparation of polybutylene succinate (PBS)/sisal‐fiber (SF) composites. The effects of mixing temperature and of steam‐explosion pretreatment of SFs on the mechanical properties of the composites were investigated, and the mechanism of action was studied by infrared spectroscopy, scanning electron microscopy, and x‐ray photoelectron spectroscopy. The results indicate that as the mixing temperature increases, PBS flows better and can graft onto steam‐exploded sisal fiber (SESF), the interfacial bond property between SESF and PBS improves, and the mechanical properties of the composites improve. The mechanical properties of the composites are maximal for a mixing temperature of 200°C. The results also demonstrate that the cellulose content and the specific fiber surface area can be increased by steam‐explosion pretreatment, so that the mechanical properties of the composites can be improved. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

废聚丙烯/废轮胎胶粉/废尼龙短纤维复合材料I.配方

用双螺杆挤出机制备了废聚丙烯／废轮胎胶粉／废尼龙短纤维(WPP／GRT／WSF)复合材料,通过正交实验得出了制备该复合材料的最佳配方,讨论了增容剂用量、氯化聚丙烯的含氯质量分数、GRT用量及其粒径、WSF用量及预处理对该复合材料力学性能的影响。结果表明,制备该复合材料的最佳配方(质量份,下同)是WPP100,GRT30,WSF8,二甲基二硫代氨基甲酸锌、二硫化二苯并噻唑、多乙烯多胺及重油用量依次为0.6,1.2,0．3,2,聚丙烯接枝马来酸酐、氯化聚丙烯用量依次为8.4;在最佳配方下,该复合材料的非缺口冲击强度为25.2kJ／m^2,拉伸强度为13．6MPa;GRT用量为30份时,该复合材料的拉伸强度和非缺口冲击强度最大,GRT的最佳粒径为40目;WSF经D法预处理后,提高了该复合材料的力学性能,拉伸强度为16．3MPa,非缺口冲击强度为27．8kJ／m^2。     

Wood‐fiber/high‐density‐polyethylene composites: Coupling agent performance

The coupling efficiency of seven coupling agents in wood–polymer composites (WPC) was investigated in this study. The improvement on the interfacial bonding strength, flexural modulus, and other mechanical properties of the resultant wood fiber/high‐density polyethylene (HDPE) composites was mainly related to the coupling agent type, function groups, molecular weight, concentration, and chain structure. As a coupling agent, maleated polyethylene (MAPE) had a better performance in WPC than oxidized polyethylene (OPE) and pure polyethylene (PPE) because of its stronger interfacial bonding. A combination of the acid number, molecular weight, and concentration of coupling agents had a significant effect on the interfacial bonding in WPC. The coupling agents with a high molecular weight, moderate acid number, and low concentration level were preferred to improve interfacial adhesion in WPC. The backbone structure of coupling agents also affected the interfacial bonding strength. Compared with the untreated composites, modified composites improved the interfacial bonding strength by 140% on maximum and the flexural storage modulus by 29%. According to the statistical analysis, 226D and 100D were the best of the seven coupling agents. The coupling agent performance was illustrated with the brush, switch, and amorphous structures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 93–102, 2005     

Polylactide‐recycled wood fiber composites

Polylactide (PLA)‐recycled wood fiber (RWF) composites with a small amount of silane were compounded using a kinetic‐mixer and molded using an injection molding machine. The molded PLA‐RWF composites were characterized using gel permeation chromatography, scanning electron microscope, X‐ray diffraction, differential scanning calorimeter, tensile testing machine, and a dynamic mechanical analyzer. As observed in the stress–strain plots, the amount of necking before fracture decreased with an increasing RWF content. Similarly, the strain‐at‐break also decreased with the RWF content. The tensile strength remained the same irrespective of the RWF content. Both the tensile modulus and the storage modulus of the PLA‐RWF composites increased with the RWF content. The degree of crystallinity of the PLA increased with the addition of RWF. No reduction in the number–average molecular weight (M_n) was observed for pure PLA and PLA‐10%RWF‐0.5%Silane composites after injection molding; however, substantial reduction in M_n was found in PLA‐20%RWF‐0.5%Silane composites. Finally, a theoretical model based on Halpin–Tsai empirical relations is presented to compare the theoretical results with that of the experimental results. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical property enhancement in short-fiber composites through the control of fiber orientation during fabrication

The mechanical properties of plastics and elastomers reinforced by short fibers are generally dictated by the selection of matrix and reinforcement. However, the high tensile properties attainable in these systems through laboratory processing techniques are frequently not obtained in conventional fabrication operations. To gain a wider latitude in meeting economic and performance constraints, the control of composite structure in the fabrication step should not be overlooked. Tool geometry and processing conditions can be manipulated specifically to control the fiber orientation distribution in the product. A study of fiber orientation in composite compounds during flow through runners, gates, and dies leads to recommendations for optimizing the directional strength and stiffness according to a kinematic model. Performance data on parts fabricated from various short-fiber composite materials bear out these projections.