Conductive PVC composites: Part 2. Processing performance

PVC-based plastics have a good record for injection-molding processability, early deficiencies having been corrected with additives. Because metallic flakes have unusual aspect ratios compared with conventional fillers, it has been necessary to determine the general effects of flake on injection molding. Specific objectives of the investigation were to verify processing latitude, set guidelines for optimum processing, determine the effects of processing on physical and electrical properties, and look for unusual effects due to filler configuration. Flow properties of the PVC composite were shown to be adequate for the majority of applications, and mold-filling ability of the PVC composite was found equal to that of flame-retarded polycarbonate and close to that of flame-retarded ABS.     

Conductive composites of PVC and wood's metal with interpenetrating network structure

This work presents composite materials with interpenetrating network structure based on thermoplastic polymer and low melting metal alloy. Composites with various alloy content were prepared by PVC powder sintering to obtain polymer matrix with open pores. Then, liquid Wood's metal was intruded into the matrix using a pressure autoclave. Obtained composites have been studied with respect to microstructure, mechanical, thermal, and electrical properties. SEM micrographs revealed good dispersion of metal in the matrix but at low loading levels it is incomplete. Addition of metal improved mechanical properties, especially flexural strength. Electrical resistivity of samples varies from 10^?4 to 10^?5 Ω m and these values are typical of conductors. The measurements of electromagnetic interference shielding effectiveness (EMI SE) shows that generally PVC/Wood's metal composites have a good ability to shield electromagnetic waves. Composites containing more than 15 vol % Wood's metal exhibited EMI SE above 40 dB in the major part of frequency range. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Material properties of nanoclay PVC composites

Nanocomposites of poly(vinyl chloride) have been prepared using both hectorite- and bentonite-based organically-modified clays. The organic modification used is tallow-triethanol-ammonium ion. The morphology of the systems was investigated using X-ray diffraction and transmission electron microscopy and these systems show that true nanocomposites, both intercalated and exfoliated systems, are produced. The mechanical properties have been evaluated and the modulus increases upon nanocomposite formation without a significant decrease in tensile strength or elongation at break. Thermal analysis studies using thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis were conducted. Thermal stability of the PVC systems was assessed using a standard thermal process evaluating the evolution of hydrogen chloride and by color development through the yellowness index. Cone calorimetry was used to measure the fire properties and especially to evaluate smoke evolution. The addition of an appropriately-modified bentonite or hectorite nanoclay leads to both a reduction in the total smoke that is evolved, and an increase in the length of time over which smoke is evolved. Along with this, a reduction in the peak heat release rate is seen. It is likely that the presence of the clay in some way interferes with the cyclization of the conjugated system formed upon HCl loss.     

Carbon-based piezoresistive polymer composites: Structure and electrical properties

Piezoresistive polymeric composites were prepared by melt mixing of polypropylene (PP) with expanded graphite (EG) (10–15 wt%) and/or multiwalled carbon nanotubes (MWCNTs) (1–2 wt%). The composites were extruded at a temperature of 185 °C, by adopting 2.5–10 rpm screw speeds, and fibres with diameters of 0.2, 1.5 and 3 mm, were obtained. An integrated piezoresistive sensor device was obtained by hot pressing the extruded fibres into two sandwiched PP panels.Structure and morphology of the carbon fillers (EG and MWCNTs) and of the fibres, were investigated by means of X-ray diffraction, optical microscopy, scanning electron microscopy (conventional and conductive SEM) and atomic force microscopy. Piezoelectric properties of fibres and sensor devices were detected through a set up made by a dynamometer, a potentiometer and a digital multimeter. It was shown, that mechanical deformations, due to the applied loads, affect remarkably the resistivity of the materials.     

Conductive network formation and electrical properties of poly(vinylidene fluoride)/multiwalled carbon nanotube composites: Percolation and dynamic percolation

Conductive network formation and its dynamic process for multiwalled carbon nanotubes (MWNTs) and carboxyl‐tethered MWNT (MWNT‐COOH) filled poly(vinylidene fluoride)(PVDF) systems were investigated. Based on real‐time tracing the variation of electrical resistivity of systems with isothermal treatment time, the conductive network formation was evaluated. It was found that the conductive network formation was temperature and time dependent. The percolation time, characterized at a certain annealing time where the electrical resistivity started to decrease drastically, decreased with the increase of the filler concentration or the annealing temperature. However, the values of the percolation time and the activation energy of conductive network formation for the PVDF/MWNT‐COOH system were higher than those of the PVDF/MWNT system, indicating that the interaction between MWNTs and PVDF molecules played an important role in the conductive network formation of the composites. Furthermore, a modified thermodynamic percolation model was proposed to predict the percolation time of PVDF/MWNT composites. It was found that the calculated results fit the experimental data very well. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Novel,low-cost jute-polyester composites. Part 1: Processing,mechanical properties,and SEM analysis

The development of high performance composites from a cheap natural fiber, jute, as reinforcement is particularly significant from an economic point of view. In this work, jute fiber-unsaturated polyester(GP) composites having appreciable mechanical properties were prepared by using solution impregnation and hot curing methods. Both unbleached (control) and bleached jute slivers with various percentages of fiber loadings were used to prepare the composites and were named JPH (C) i.e., Jute Polyester Hot Curing (control), and JPH (B) i.e., Jute Polyester Hot Curing (bleached), respectively. Mechanical properties such as tensile and flexural strain, toughness, and moduli of both the grades have been compared. Composites having 60 wt% of jute fiber yielded the best results. JPH (B) showed much better flexural properties than JPH (C), although the tensile properties of the latter were better. The inter-laminar shear strength (ILSS) of the JPH (B) was found to be higher than JPH (C). The nature of fiber-resin bonding was studied from scanning electron micrographs of the specimens subjected to tensile and flexural fracture. Dynamic mechanical properties were found to be very high, superior even to those of glass fiber reinforced composites. The flexural storage modulus was found to be 12.3 GPa at 30°C and to decrease slowly with temperature. The major finding in this work is the attainment of high mechanical properties of composite specimens with 60 wt %fiber loading. On a weight and cost basis, bleached jute fibres were found to be better reinforcements than other fibers with usual surface modification by coating or grafting processes.     

Friction and wear properties of NBR/PVC composites

Acrylonitrial butadiene rubber (NBR)/Polyvinyl chloride (PVC) composites with different PVC content were prepared. The effect of PVC content on the mechanical strength and tribological properties of the NBR/PVC composites was investigated. The morphologies of the worn traces and debris of NBR/PVC composites and worn traces of mating ball were observed using a scanning electron microscope (SEM). It was found that the friction and wear of NBR/PVC was lower than that of NBR without PVC. The NBR/PVC composite with 30% PVC content showed the best synthetic mechanical and tribological properties. The inferior elastic properties and the lesser deformation under the applied load of composites with PVC resulted in hysteric force and adhesion force decrease, which leading to a lower friction and wear of NBR/PVC composites. The frictional failure unit of NBR70/PVC30 composite being smaller should be an important reason of the wear of the composite being lowest. The lubricating effect of PVC played an important role in decreasing the friction coefficient and wear of NBR/PVC composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

PVC/高岭土复合材料的制备及其力学性能研究

针对PVC加工过程中韧性差、冲击强度低、热不稳定等问题,制备了PVC/N-十六烷基马来酰胺酸镧(Ⅲ)-高岭土复合材料。通过刚果红实验、傅里叶红外光谱(FTIR)、X-射线衍射(XRD)、热重分析(TGA)等表征了其结构与热性能;通过扫描电镜(SEM)观察复合材料表观形貌;研究了插层后的高岭土对PVC材料抗冲击强度的影响。结果表明,插层改性后的高岭土层间距增大;PVC复合材料圆形度得到了提高,外形变得更加规整;获得的复合材料断裂伸长率和冲击强度都有所增强,复合材料的热稳定性能也得到了提高。     

Mechanical properties of injection molded long fiber polypropylene composites,Part 1: Tensile and flexural properties

Innovative polymers and composites are broadening the range of applications and commercial production of thermoplastics. Long fiber‐reinforced thermoplastics have received much attention due to their processability by conventional technologies. This study describes the development of long fiber reinforced polypropylene (LFPP) composites and the effect of fiber length and compatibilizer content on their mechanical properties. LFPP pellets of different sizes were prepared by extrusion process using a specially designed radial impregnation die and these pellets were injection molded to develop LFPP composites. Maleic‐anhydride grafted polypropylene (MA‐g‐PP) was chosen as a compatibilizer and its content was optimized by determining the interfacial properties through fiber pullout test. Critical fiber length was calculated using interfacial shear strength. Fiber length distributions were analyzed using profile projector and image analyzer software system. Fiber aspect ratio of more than 100 was achieved after injection molding. The results of the tensile and flexural properties of injection molded long glass fiber reinforced polypropylene with a glass fiber volume fraction of 0.18 are presented. It was found that the differences in pellet sizes improve the mechanical properties by 3–8%. Efforts are made to theoretically predict the tensile strength and modulus using the Kelly‐Tyson and Halpin‐Tsai model, respectively. POLYM. COMPOS., 28:259–266, 2007. © 2007 Society of Plastic Engineers     

Physical gels from PVC: dynamic properties of dilute solutions

In an effort to gain information on the gelation mechanism of poly(vinyl chloride) (PVC) in diethyl malonate, investigations of dilute PVC solutions were made using transient electric birefringence, flow birefringence, dynamic light scattering and viscometry. The dynamical structure factor obtained from the cumulant analysis of the autocorrelation function of scattered field exhibits an anomalous K dependence which can be attributed to an intramolecular effect. Measurements of intrinsic viscosity and rotational diffusion coefficient provide information on the internal structure of the aggregates formed by quenching dilute PVC solutions.     

Lignin-polypropylene composites. Part 1: Composites from unmodified lignin and polypropylene

Lignin polypropylene composites were prepared in the range of 10–60% by weight lignin content. Blending of lignin with polypropylene resulted in materials with reduced tensile and flexural strength and a dramatic decrease in unnotched Izod impact strength compared to the properties of virgin polypropylene, although moduli (Young's and flexural) were improved. Traditional surface-treated fillers such as mica and talc performed better than lignin, but when lignin and inorganic fillers were mixed, the strength properties were improved with respect to lignin alone, perhaps because of a better lignin-filler-particle interaction and distribution. This could be an alternate approach for obtaining improved strength composites containing large quantities of unmodified kraft lignin. Incorporation of maleic anhydride grafted polypropylene (MAPP) as a coupling agent also improved strength properties, although at high lignin contents (e.g. 60%) there was considerable variability in the tensile strength.     

改性无机黏土/PVC复合材料的制备及性能

比较了3种无机黏土(超细无机黏土A、偶联剂表面改性无机黏土B、实验室自制大分子表面处理剂DF包覆改性无机黏土C)对PVC材料力学性能、微观形貌的影响,重点研究了无机黏土C对PVC材料动态力学性能、耐热性能的影响。结果表明:①适量添加无机黏土可以提高PVC材料的拉伸性能和冲击性能;②无机黏土C/PVC复合材料具有很好的耐热性能;③无机黏土C的填充效果较好。     

Characterisation and properties of geopolymer composites. Part 2: Role of cordierite-mullite reinforcement

Our previous research paper on geopolymer-mullite composites showed promising results on compressive strength and fire resistance. However, no improvement in thermal shock resistance was observed in the afore mentioned study. In this study, further attempts to improve thermal shock resistance of the geopolymer were explored. The research was performed by compositing a fly ash-based geopolymer with cordierite-mullite at 20, 40 and 60 wt% replacement. X-ray diffraction (XRD) of the cured geopolymer composite specimens showed the existence of cordierite, mullite, quartz, cancrinite and lazurite. It was found that compressive strength and strength retention after thermal exposure at 400 °C were improved in the geopolymer composite specimens, especially those with 20–40 wt% replacement. Upon further heating to 600 °C, all geopolymer specimens showed insignificant differences in compressive strength. Fire resistance was found to improve with increasing proportion of replacement contents.     

The electrical properties of magnetite-loaded polyethylene composites

Magnetite–polyethylene composites containing various concentrations of magnetite have been prepared and their electrical properties have been investigated. The electrical resistivities of the specimens were studied as function of filler concentration and temperature. The current density-electric field characteristic and the current variation with time were measured. The thermionic and field emission models provide good explanations for the electrical conduction in the specimens, and space-charge-limited conduction is discussed based on the results.     

抗静电PVC-U复合材料的性能研究

将炭黑或石墨作为导电填料,制备了一系列PVC-U抗静电复合材料。研究了导电填料品种与用量及加工条件对PVC-U复合材料的导电性能、加工性能及力学性能的影响。结果表明:炭黑与石墨在PVC树脂中呈连续网络状不均匀分散;当炭黑含量低时,制品既具有良好的导电性能,又具有良好的熔体流动性。     

Modelling of electrical properties of Ni-YSZ composites

Ni-YSZ cermets with tailored microstructural characteristics are of interest in many solid-state electrochemical applications such as fuel cell electrode processes or oxygen sensors. In order to elucidate the role of microstructural parameters on overall Ni-YSZ electrical characteristics, different cermets were synthesized by the citrate–nitrate combustion route and their electrical characteristics were tested. The combustion derived samples exhibited fairly high electronic conductivity, even at a relatively low metal volume fraction of 24 vol.% of Ni. To determine the electrical conductivity behaviour of the composites in a broad range of metal content and its relation to material porosity, the general effective media approach and the sine-wave approximation were used, respectively.     

Studies on poly(vinyl chloride)-copper composites. Part 1: State of segregation of filler particles,electrical and mechanical properties in presence of plasticizer and stabilizer

The presence of additives influences the state of segregation of filler particles in the polymer matrix which in turn controls the electrical and mechanical properties of poly(vinyl chloride)-copper composites. The liquid plasticizer seems to form a coating on the filler surface which introduces quasirandomness in the segregated network. In accordance with the mathematical model proposed earlier, the strength properties were found to be proportional to d_m^?½ where d_m is the mean free path between the filler particles. Calculations of d_m were based on two different models, one for segregated network (unplasticized and low plasticized composites) and the other for quasi-random distribution of filler particles (plasticized composites). Extruded samples in general show more randomness in the filler distribution than the compression molded samples.     

Rheology of PVC. Part 5: Melt elasticity

The behavior of PVC changes drastically with the temperature and the method of sample preparation. In the steady-state shear mode, upon a decrease of the rate of deformation, the data may show either a steady increase of the shear viscosity or a leveling off to a Newtonian plateau. In the dynamic test mode, both the storage modulus, G′, and the loss modulus, G″, show an effect of the yield stress. Only at temperatures above 210°C are flow curves normal for polymer melts obtained. Rigid and nonrigid PVC formulations have been tested in Weissenberg Rheogoniometer, using steady-state or dynamic test modes at temperatures from 140 to 220°C. It was observed that yield affects elasticity more (measured by the first normal stress difference or the storage modulus) than viscosity (expressed by the shear stress or the loss modulus). The corrected for yield plots of elastic vs. viscous parameter can be easily interpreted in terms of a composite flow.     

Thermal and electrical properties of some epoxy based composites

Thermally stimulated creep compliance, differential scanning calorimetric behavior, thermal degradation, AC dielectric permittivity and loss (between 120 Hz and 100 kHz) and thermally stimulated polarization and aepolarization currents were studied in a cycloaliphatic epoxy resin (B), in a conventional bisphenol-A-diglycidyl ester type epoxy resin (C) and in composites consisting of: resin B/wollastonite (B/W), resin B/quartz (B/Q) and resin C/wollastonite (C/W). The filler content was 60 wt%. Resin B exhibited higher T_g and lower rubbery deformability than resin C due to its more compact structure. Fillers reduced the rubbery deformation and thermal expansion and shifted the transition temperatures by a few degrees. The shift depended on the method used. Composites B/W and C/W exhibited higher thermal stability than the corresponding pure resins, while sample B/Q was less stable than resin B. Resins B and C exhibited a low temperature β transition (in the case of resin B a doublet) and a high temperature α or glass transition. AC dielectric losses were fairly similar in samples B and B/W, while the high temperature loss of sample B/Q was determined by a space charge process probably due to the matrix/filler interface. In samples C and C/W the α transition is visible but it is superposed on a strong space charge process due to the resin/electrode interface. Thermally stimulated currents show a behavior qualitatively in agreement with the AC results but the very low effective frequency and the nonlinear field strength dependence of the space charge processes cause some minor differences.     

The properties of recycled PVC bottle compounds. 1: Mechanical performance

The properties of recycled PVC bottle material separated from the post-consumer waste stream were investigated. In the first part of this study, attention was focused on the mechanical properties. In order to examine the effects of recycling, the properties of the recycled material were compared with those of virgin PVC and pure material that had been processed into bottles and then granulated. The effects of pulverization of the recycled material were also studied. The mechanical properties investigated included tensile, fatigue, and environmental stress cracking tests, in conjection with fracture surface examination, molecular weight determination, and impurity analysis. It was found that the recycled material did show significant reduction in strength and ductility, though pulverization improved the situation considerably. The main reason for this was the presence of impurities, especially PET, which although present at levels below 0.5% had a large effect on the properties.