Showing papers in "Polymer-plastics Technology and Engineering in 2000"

Acetylated plant-fiber-reinforced polyester composites: a study of mechanical, hygrothermal, and aging characteristics

Abstract: The potential of acetylation of plant fibers to improve the properties of composites was studied. The chemical modification of oil palm empty fruit bunch (EFB), coconut fiber (Coir), oil palm frond (OPF), jute, and flax using noncatalyzed acetic anhydride were investigated. Proof of acetylation was indicated by the increase in weight percent gain (WPG). Acetylation at a reaction temperature of 120°C had resulted in the reduction in the tensile properties (stress, modulus, and elongation at break) of EFB and Coir composites. However, at 100°C, the acetylated samples exhibited improved properties. The mechanical properties of acetylated EFB- and Coir-fiber-reinforced polyester composites was evaluated at different fiber loadings. The tensile strength and modulus were improved, but elongation at break was slightly reduced upon acetylation, particularly at high fiber loading. Impact properties were moderately increased for those composites with fiber loadings up to 45%. Acetylation exhibited a low moisture ab...

Morphological characterization and mechanical behavior of sponge gourd (luffa cylindrica)–polyester composite materials

Abstract: The use of sponge gourd (Luffa cylindrica) as reinforcement in resin matrix composite materials is evaluated. The morphology of the fibrous vascular system of Luffa's fruit is presented and the advantages of using this natural mat material are highlighted. The use of untreated Luffa does not increase the mechanical properties of the bare resin. Nevertheless, its incorporation produces a change on the fracture mode of the composites from an abrupt one to a controlled and safer one. This result and the values obtained from mechanical tests show that, without any surface treatment, Luffa already has a high potential use as a core material in hybrid composites.

A study on mechanical performance of jute-epoxy composites

Abstract: Jute fibers in the form of slivers have been reinforced with epoxy resins to prepare composites. The solution impregnation method has been adopted in an attempt to increase the percentage of fiber loading. Both untreated (control) and chemically modified (bleached) slivers have been used to prepare composites. The optimization study of fiber loading in composites is done with control slivers through tensile property assessment. Composites having 50% sliver (control) by weight are observed to give the best tensile characteristics. The tensile, flexural, impact, and hardness properties of the composites of both bleached and control slivers have been investigated and it is observed that although the latter have better tensile properties, the former possesses unusually high flexural properties. Both Izod and Charpy impact tests reflect that the composites with bleached slivers have higher impact strengths. In comparison to the composites with control slivers, they also exhibit greater (Rockwell) hardness.

Environmentally friendly processing of polyurethane foam for thermal insulation

Abstract: An environmentally friendly processing method of polyurethane foam was proposed and evaluated for the application of thermal insulation. For the production of polyurethane foam, chlorofluorocarbon (CFC) gases were eliminated to minimize environmental destruction. Carbon dioxide gas was used as a blowing agent instead of the CFC gas. Ultrasonic excitation was also applied to the mixture of polyol and isocyanate to increase the rate of nucleation and decrease the thermal conductivity. Nucleation and growth of bubbles were studied theoretically and experimentally. Water was used as a chemical blowing agent and carbon dioxide gas as the physical blowing agent. Experiments were carried out with different saturation pressures, and experimental results were evaluated to determine the best foaming conditions. Rate of bubble nucleation, final bubble sizes, conversion during polymerization reaction, and other parameters were predicted theoretically with the assumption that negative pressure is generated by the ultr...

Cure characteristics and mechanical properties of natural rubber/reclaimed rubber blends

Abstract: Cure characteristics and mechanical properties of natural rubber/reclaimed rubber blends were studied. The minimum torque values of the blends were lower than that of the gum compound. The (maximum–minimum torque) and scorch time decreased with increasing reclaim content. The cure rate of the blends were lower than that of the virgin compounds. The tear strength was improved by the addition of reclaimed rubber. Tensile strength, elongation at break, and resilience decreased with increasing reclaim loading. The heat buildup was higher for the blends.

Thermal degradation of natural rubber/styrene butadiene rubber latex blends by thermogravimetric method

Abstract: Thermal properties of natural rubber (NR)/styrene butadiene rubber (SBR) latex blends made from latex blending have been investigated using thermogravimetric analysis. It was found that the initial degradation temperature of NR is lower than SBR, and on addition of SBR, the degradation temperature is increased, indicating increased thermal stability of the blend. The main degradation products of NR contain isoprene and dipentene and that of SBR contains a large number of products like 4-vinyl cyclohexene, styrene, methylbenzene, and so forth. In addition to that, the temperature at which 50% and 75% degradation of NR occurs is increased upon the addition of SBR. Vulcanization increased the thermal stability of NR/SBR blends slightly. The activation energies for the degradation of the blends are higher than that of the homopolymers.

Novel low-cost jute–polyester composite. ii. sem observation of the fractured surfaces

Abstract: The scanning electron micrographs (SEM) were taken at different magnifications with respect of the fractured surfaces of the polymer composites prepared from unsaturated polyester resin and jute sliver with 60% fiber loading by weight. The composite specimens were prepared using both untreated (control) and chemically modified (bleached) jute fibers by solution impregnation and hot curing methods and are designated as JPH-60(C) and JPH-60(B), respectively. The method of preparation of the composite specimens have been discussed. The specimens were subjected to tensile and flexural tests and the fractured surfaces were observed under SEM as stated. The fiber surface morphology was also studied from the SEM photographs in the case of the control and bleached jute filaments. The SEM photographs of the fractured surfaces of the composites showed varied extents of fiber pull-outs under both tensile and flexural failure modes. The nature of interfacial adhesion has been discussed on the basis of the SEM study. ...

Study of the curing process of an epoxy resin by ftir spectroscopy

Abstract: The curing process of an epoxy resin of glycidic polyether by Fourier transform infrared spectroscopy has been studied. The influence of the hardener/resin ratio, temperature, and curing time have been determined. This article discusses which bands of the infrared spectrum and what relation of their absorbances are most convenient to monitor the resin-curing process.

Tensile property of epoxidized natural rubber/natural rubber blends

Abstract: The tensile strength and elongation at break of epoxidized natural rubber (ENR) blended with natural rubber (NR) was studied. ENR 25, ENR 50, and one grade of natural rubber (SMR L) were used as the elastomers. The composition of ENR was varied from 0% to 100% rubber. The accelerated sulfur vulcanization system was used throughout the investigation. The tensile property of unaged and aged samples was determined by using the Monsanto tensometer (T10) operating at 50 cm/min. Results show that the tensile strength and elongation at break passes through a maximum at 50% ENR for both ENR25/SMR L and ENR50/SMR L blends. This positive deviation from ideality is attributed to the mutual reinforcement of ENR and NR in the blends as a result of strain-induced crystallization. This synergistic effect is more pronounced in the case of ENR 25 due to the higher crystallinity and availability of more double bonds, which is more compatible to NR compared to ENR 50/NR blends. For the aged samples, a drop in the tensile pr...

DIRECT CENTRIFUGAL MOLDING OF NYLON 6-BASED PRODUCTS FROM ϵ-CAPROLACTAM

Abstract: Previously synthesized polymers (pellets or powders) and reactive monomers (lactams) can be used as starting materials in direct centrifugal molding for the manufacture of products with a circular section. The direct centrifugal molding of ϵ-caprolactam has been investigated in order to obtain Nylon 6-based products as well as to study the influence of process variables (e.g., initial mold temperature) on the degree of crystallinity and mechanical properties of the finished moldings. At initial mold temperatures greater than 140°C, a significant reduction of the degree of crystallinity, an increase of the Izod impact strength values, as well as a decrease of the flexural modulus values were observed.

Friction and wear behaviors of toughened polyoxymethylene blend under water lubrication

Abstract: This article describes the results from an experimental investigation on the friction and wear performances of the toughened polyoxymethylene/polyurethane blend (M-POM) under water drops lubrication. The sliding experiments were carried out on a block-on-ring tribometer. The contact configuration used was a stationary polymer block on a rotating AISI 1045 steel or MC nylon ring. The selected test material includes a polyoxymethylene (POM)-based composite that was toughened by polyurethane (PU) and filled by polytetrafluoroethylene (PTFE) and silicone oil. The results show that the M-POM with 10% PU (by weight) has better antifriction and antiwear properties under water drops lubrication, compared with pure POM and the POM/PTFE composite. The M-POM is more suitable to slide against MC nylon than steel under water lubrication. Because of the entrance of water, the hydrogen bond formed between water and polymers at the frictional surfaces during friction improves greatly the water lubrication performance of ...

Effect of bonding systems on the adhesion of nitrile rubber to nylon cord

Abstract: A tricomponent system composed of resorcinol, hexamethylene tetramine (HMT), and hydrated silica was used as an adhesion promoter with a nitrile rubber (NBR) mix. The resorcinol was replaced by o-aminophenol, m-aminophenol, p-aminophenol, or m-phenylene diamine. The rubber–textile cord samples were subjected to aging or exposed to ionizing radiation and their adhesions were examined. The effect of the cross-link density of different nitrile rubber mixes on the adhesion was also studied. The results showed that aminophenols and m-phenylene diamine used have an effect on the adhesion. However, their adhesion levels are lower than those obtained by resorcinol. The results also showed that, on aging, m-aminophenol and m-phenylene diamine have either better stability or enhancement of adhesion levels than other bonding systems. On exposure to radiation, the results showed that the bonds formed between NBR mixes, containing different types of bonding material, and undipped nylon cords are more stable than those...

Review of volatile organic compounds derived from polyethylene

Abstract: The formation of volatile organic compounds (VOCs) in polyethylene (PE) is a topic of concern to industries involved in the packaging of items such as foodstuffs and pharmaceuticals that are sensitive to organoleptic contamination. This article reviews the available literature on VOCs that originate from PE during its manufacture, processing, storage, and service life. The package–product interactions that may occur between PE and packaged foodstuffs are also considered together with the wide range of methods for the analysis of VOCs. The following analytical methods are discussed: (i) sensory evaluation, (ii) chromatographic techniques and their associated sampling techniques, including the “hot-jar” method and dynamic headspace sampling, (iii) gas chromatography–olfactory sensing, and (iv) artificial olfaction or “electronic nose” technology.

Effects of shear and thermal history on the microstructure of solution polymerized poly(methyl methacrylate)–clay composites

Abstract: Poly(methyl methacrylate)–clay composites were synthesized through free-radical solution polymerization of methyl methacrylate in the presence of clay that was preintercalated with dodecylammonium or hexadecyltrimethylammonium ions. Neither the diffraction peak from the (001) plane nor the 00l reflections for the (001) plane were observed during x-ray characterization, showing that the clay particles were greatly expanded (i.e., exfoliated) in the reaction products, due to the presence of large quantities of polymer between the clay layers. Syntheses carried out with high clay loadings resulted in reductions in the weight and number-average molecular weights and increases in the polydispersities of the polymers, caused by chain transfer to active sites on the surface of the clay. It was found that heat and shear, during subsequent processing of the reaction products, resulted in reordering of the microstructure through narrowing of the clay galleries with the partial exclusion of the polymer. The final in...

Phase-separation behavior in poly(ether imide)-modified epoxy blends

Abstract: Phase-separation behavior of aromatic amine-cured diglycidyl ether of bisphenol-A (DGEBA) epoxy oligomer and poly(ether imide) (PEI) engineering thermoplastic-modifier mixtures was investigated by means of small-angle light scattering (SALS) and optical microscopy. The starting reactant mixtures comprising epoxy, PEI, and the curing agents, namely diamino diphenyl sulfone (DDS) and methylene dianiline (MDA), were found to be single phase. During curing, phase separation occurred in the epoxy/PEI/DDS system, whereas no phase separation took place in MDA-cured epoxy/PEI blends. The difference between the two systems has been attributed to thermodynamic and kinetic aspects of cure reaction in thermoplastic-modified thermosetting (TMT) polymeric blends. Spinodal decomposition as characterized by an increase of scattered intensity, shift of the peak angle to a smaller scattering angle, and development of a regularly phase-separated structure followed by coarsening was found to be the dominant mechanism of reac...

Instrumented impact behavior of particulate-filled composites

Abstract: A study of the influence of calcium carbonate on impact energy of CaCO3/high-density polyethylene composites was conducted Composites with calcium carbonate in the range of 0–40% were produced by twin-screw extrusion followed by compression molding Notched Izod impact tests of composites were carried out using an instrumented impact tester It was found that increasing the calcium carbonate content decreased impact resistance Transition in total impact energy with filler content was observed at 20% filler volume fraction, similar to propagation energy In the case of the initiation energy, the transition was found at a different level, 10% filler volume fraction The impact fracture process of polyethylene was seen to be initiated by crazing, followed by brittle failure, whereas composites were initiated by microvoid nucleation from interfacial failure between the filler and matrix and were propagated via microvoid coalescence

Morphologically special features of poly(3-hydroxybutyrate)/low-density polyethylene blends

Abstract: In an effort to investigate the morphology of biodegradable films, the combination of differential scanning calorimetry, scanning electron microscopy, and Fourier transform infrared polarization spectroscopy methods are used. The methods enable one to examine the structural and morphological peculiarities of extruded blend compositions on the base of low-density polyethylene (LDPE) and poly(3-hydroxybutyrate) (PHB) at concentrations of the latter ranges from 0 to 32 wt%. The blend components are thermodynamically incompatible and form the proper morphological elements with good visible interfaces between the disperse phase (PHB) and the continuous matrix LDPE. For film extrusion, blend components affect each other, as is seen by the crystallinity drop for both PHB and LDPE. The dichroism measurements show that the axes of LDPE and PHB molecules are presumably located at right angles, therewith the largest axes of the PHB crystallites are oriented along the extrusion direction. The matrices at all blend ra...

Effect of addition of various acrylates on the performance of ethyl cyanoacrylate adhesive

Abstract: Polyalkyl 2-cyanoacrylates begin to retropolymerize and deteriorate dramatically at temperatures above 80°C. They bond rapidly to the metal surfaces and readily lose strength even at ambient temperatures. These two drawbacks of the cyanoacrylates have made this class of adhesives unpopular as structural adhesives. Several attempts have been made to increase the thermal stability and the stability of the bond between the metal surfaces by adding chemicals like cyclopentadienoates and anhydrides to the cyanoacrylates. Cyclopentadienoates are not available commercially, and, therefore, in this study, we have selected various acrylates and methacrylates in the cyanoacrylate formulation and these were tested to various temperatures. Interesting results have been obtained and reported.

High water absorbents from lignocelluloses. i. effect of reaction variables on the water absorbency of polymerized lignocelluloses

Abstract: Hydrogels of 350 water-absorbency (g H2O2/g sample) and 900 water-keeping capacity (mL H2O2/g sample) were prepared from local lignocellulosic wastes. The wastes used are rice straw, sugar-cane bagasse, and cotton stalks. These hydrogels were prepared via graft–polymerization reaction using some vinyl monomers, followed by alkali hydrolysis. The effects of grafting parameters (concentration of both initiator and monomer, temperature, and time), purity of lignocellulose sample, type of monomer, pretreatment of lignocellulose, and manner of saponification reaction were examined. The application of such polymeric materials as soil conditioners, by following the pore size distribution of sand soil, in comparison with conventional soil conditioners (e.g., natural organic fertilizer and clay), were also evaluated.

Acrylonitrile–butadiene rubber stabilized by methacrylamides as antioxidants

Abstract: Methacryloyl chloride was reacted with 4-amino and 4-thiophenols to provide the corresponding methacrylamides. These compounds were incorporated in NBR mixes to be evaluated as antioxidants for NBR oil-seal products in comparison with the industrial antioxidant phenyl-B-naphthylamine (PBN). The mechanical, swelling, percentage volume extraction, and compression recovery properties of the produced rubber vulcanizates were assessed. It has been found that the prepared antioxidant N-(4-hydroxyphenyl)methacrylamide (4-HPM) is superior for swelling and compression recovery of oil-sealing products.

Kinetic aspects of aging of poly(vinyl chloride)-based polymer materials

Abstract: The results of the complex study of samples of plasticized poly(vinyl chloride) (PVC) subjected to aging under model and climatic conditions or being in use for a long time (from 15 to 30 years at 253–301 K) studied by various techniques and the mechanism of their aging are presented in the article. Using the thermogravimetric, chromatographic, ultraviolet and infrared spectroscopic techniques, gel permeation chromatography, mercury porosimetry, and techniques for measuring mechanical strength properties of the materials (e.g., tensile strength and strain), we have shown that the service and functional properties of plasticized PVC were lost as a result of diffusion-controlled desorption of a plasticizer or other additives. Information about the aging conditions can be derived from the experimental time histories of the weight loss or additive depletion in the course of functioning of PVC samples or their exposure to different impacts. These experimental data are used to formulate a mathematical descripti...

Rheological properties of the dispersions of starch, guar gum, and their physical mixtures in the temperature interval 298.15–333.15 k

Abstract: This article reports on the experimental data on rheological properties such as torque, viscosity, shear stress, and shear rate for the aqueous dispersions of starch, guar gum, and their physical mixtures in the temperature interval 298.15–333.15 K using a Brookfield rheometer. The data have been obtained for both the non-cross-linked and cross-linked polysaccharide dispersions using the urea formaldehyde prepolymer. Furthermore, the results have been analyzed using the equations of Bingham, Casson, power-law, and IPC paste analysis. The Gibbs free energy of activation, changes in enthalpy, and entropy for the dispersions have also been calculated. It is found that the cross-linked starch and guar gum dispersions are more stable and more viscous than the individual dispersions.

Sorption, diffusion, and permeation of chlorinated hydrocarbon vapors through natural rubber, epoxidized natural rubber, and their blends

Abstract: The study investigates the transport process of various chlorinated hydrocarbons through natural rubber (NR), epoxidized natural rubber (ENR), and their blends. The effect of structure and morphology of the membranes on the transport parameters has been investigated. Sorption coefficient is found to increase and the permeability coefficient shows the reverse trend with increasing epoxy content. As the mol% epoxidation increases, the polymeric network structure becomes more compact, which leads to a decrease in the diffusion coefficient, which ultimately results in a low permeation coefficient. The morphology of NR/ENR blends has been investigated by combining scanning electron microscopy with permeability measurements. The permeation coefficient is found to be minimum for the NR/ENR 70/30 composition; a 50/50 composition shows the maximum. The heterogeneous morphology of 70/30 NR/ENR blend results in the low permeability coefficient, whereas the co-continuous nature of the 50/50 composition accounts for t...

Characterization of polymer complexes by thermal and ir spectral analyses

Abstract: The characterization of polymer complexes were studied by thermal and infrared (IR) spectral analyses from room temperature to 1000°C and from wave number 4000 cm−1 to 200 cm−1, respectively. The polymer complexes were those prepared from cellulose ether (e.g., carboxymethyl cellulose and hydroxyethyl cellulose) with some transition metals (e.g., CrCl3, FeCl3, CuCl2, CoCl2, and NiCl2). The thermal analysis measurements, such as activation energy (Ea ) and order of degradation (n), were calculated from nonisothermal thermogravimetric analysis, using the Coats-Redfern equation and the least squares method. The results obtained show that the complexation of cellulose ether with most mentioned metal ions improved their thermal stabilities. There is a relationship between the measurements of thermal analysis and the degree of ligand–metal–σ bond (nephlauxetic parameter, β), electronegativity of the metal cation, and the chelating sites of the ligand. The IR-spectra measurements, such as the shift of the band m...

MOLECULAR CHAIN STRUCTURE OF THERMOTROPIC p-OXYBENZOATE/ETHYLENE TEREPHTHALATE/VANILLATE OR PHENYLENE TEREPHTHALATE TERPOLYMERS

Abstract: Fourier-transform infrared (FTIR) and proton nuclear magnetic resonance (NMR) spectroscopies and wide-angle x-ray diffraction were used to analyze the molecular chain structures of thermotropic liquid-crystalline terpolymers from p-acetoxybenzoic acid, polyethylene terephthalate, and p-acetoxyvanillic acid, or 1,4-diacetoxybenzene/terephthalic acid. The general features of FTIR spectra of the oriented terpolymer films and NMR spectra for the terpolymers in solution with the variation of terpolymer composition are discussed. The assignments of the resonance peaks in FTIR and proton NMR spectra are given. The number-average degree of polymerization of the terpolymers is estimated to be up to 34 by end-group analysis based on the NMR spectra. The meridional scans of x-ray diffraction of the as-drawn terpolymer ribbons are being used to characterize the aperiodic characteristics and persistence length of the terpolymer chain. The persistence length of the terpolymers seems to increase with an increase in the ...

Effect of fiber reinforcement on thermal stability and swelling behavior of cr/nbr blends

Abstract: The effect of type, length, and denier of fibers on the thermal stability and swelling behavior of chloroprene/butadiene–acrylonitrile rubbers (CR/NBR) composites was investigated. The results reveal that Nylon 6 fibers improved mechanical properties, thermal stability, and swelling resistance in toluene of 50/50 CR/NBR blends. Of all fiber types investigated, the viscose fiber CR/NBR composite has the best swelling resistance in motor oil, whereas the polyester (PET) fiber composite has the best swelling resistance in brake fluid. The effect of Nylon 6 fiber loading up to 30 phr was tested in terms of mechanical properties of the composites and swelling in toluene and oils. Also, the reinforcement of white-filled blends were examined. Nylon 6 fiber loadings (15–30 phr) showed promising results, and the white-filled Nylon 6 composites showed a significant reinforcement with regard to mechanical properties and thermal stability.

Electrical properties of polymer/low-melting-point alloy binary systems

Abstract: In this preliminary experiment, Sn-Pb-alloy-powder-filled polystyrene composites were prepared and the influence of processing conditions on the electrical behavior was studied in terms of percolation transition, temperature-resistivity transition, and the heating-cooling reversibility.

Electromechanical behavior of natural rubber—lignocellulosic material composites

Abstract: The mechanical and electrical properties of the natural rubber vulcanizates loaded with lignocellulosic materials were studied. It was found that the stress of vulcanizates decreased with initial fiber loading. Also, it was shown that the presence of fibers and an adhesion system greatly improves the aging resistance of the rubber composites. The resistivity ρ, dielectric permittivity ϵ′, and dielectric loss ϵ″ of the investigated samples were determined in the frequency range 102–105 Hz at room temperature. It was noticed that ϵ′ for bagasse pulp (Bp) is higher than that for cotton stalks pulp (Csp), which is attributed to the higher hemilignin content in Bp which is characterized with a low degree of polarization. An abrupt increase of ϵ″ at a higher content of Bp was noticed.

Thermal deformation of a photo-cured polymer for the analysis of stereolithography

Abstract: Thermal deformation and residual stresses generated in the stereolithography product must be understood in order to employ the three-dimensional stereolithography for high-precision model building. The purpose of this study is to understand how residual stresses are generated in the three-dimensional stereolithography by solving the governing equations for heat transfer and nonlinear polymerization reaction kinetics simultaneously with finite-difference/finite-element numerical methods. Two cases were considered for the basic understanding of stereolithography. One is when the laser beam stays at one point and the other is when the laser scans along one line. In both cases it is possible to determine the rate of polymerization, heat generation, and the heat-transfer rate in the two-dimensional domain at any time. As the result of numerical prediction, the distribution of temperature, thermal stress, rate of polymerization, percent conversion, photo-initiator concentration, and laser-light intensity was ob...

Reinforcement of the aromatic polyamide poly(trimethylhexamethylene terephthalamide): comparisons among blended ex situ silica with and without a bonding agent and in situ generated silica

Abstract: Samples of poly(trimethylhexamethylene terephthalamide) were first blended with separately prepared fumed silica in the absence of a coupling agent, and their mechanical properties were measured in continuous extension. The reinforcement obtained in this ex situ approach was qualitatively similar to that obtained by the in situ generation of silica in the sol–gel hydrolysis and condensation of tetraethoxysilane. The increase of ultimate (tensile) strength, however, was only 10%, compared to the 25% obtained in the in situ approach. Adding 20 or 40 mol% of an epoxysilane coupling agent to the ex situ samples gave increases in tensile strength up to 50%. Scanning electron microscopy showed interesting differences in the structures of these various fillers. For example, the fumed silica particles without the coupling agent showed a tendency to form heterogeneous aggregates in a spherical texture. The particles coated with the coupling agent showed little aggregation and evidence of good adhesion to the polya...