Foaming conditions of high density polyethylene–natural rubber blends

Abstract

Foams made from high density polyethylene (HDPE) and natural rubber (NR) blends, using azodicarbonamide as a chemical blowing agent, have been investigated to establish a relationship between the structure and physical properties. The blends of HDPE, NR, epolene wax, chemical blowing agent, and necessary ingredients were prepared on a two roll mill. Subsequently, foamed structures of the blends were obtained by a single stage compression moulding. Results indicate that foaming process variables, i.e. heating time, blowing agent loading, ratio of HDPE/NR, crosslinking agent loading, and ratio of HDPE/NR at a fixed crosslinking agent loading, affect the physical properties of the foams. Attempts were made to relate such properties as foam density, hardness, tensile strength, elongation at break, tear strength, flexural strength, elastic modulus, and gel content to the foam structure. The foam structure was investigated using optical microscopy, in terms of the average cell size and its distribution.     

Flow properties of vacuum gas oil–low density polyethylene blends

In this paper, the viscous flow behaviour of Vacuum Gas Oil (VGO) with different fractions (0–10% wt.) of Low Density Polyethylene (LDPE) under dynamic shear has been investigated. Viscosimetry measurements of the blends at temperatures between 333 and 433 K using a BOHLIN Controlled Stress Rheometer, as well as compatibility studies using Differential Scanning Calorimetry (DSC) were carried out. The effects of the variation of the blends polymer content on the activation energy of flow has also been investigated. The results obtained reveal that the blends show Newtonian flow behaviour at higher temperatures for all polymer concentrations studied, while at lower temperatures and at higher polymer concentrations, they show non-Newtonian shear-thinning behaviour. Furthermore, at lower temperatures, these behaviours are more pronounced at lower shear rates than at higher shear rates. As the polymer content in the blend is increased, the shear viscosity increases, the flow behaviour index decreases, and the application of an Arrhenius type equation shows an increase in the activation energy of flow at the lower shear rates.     

Effect of nanosized reinforcement particles on mechanical properties of high density polyethylene–hydroxyapatite composites

Abstract

The effect of nanoscaled hydroxyapatite (HA) filler particles on the mechanical properties of the high density polyethylene–hydroxyapatite (HDPE–HA) composite samples has been investigated. Nanosized HA particles with an average size in the range of 40–50 nm were synthesised by mechanical milling method. The composite samples with various amounts of nanoscaled HA particles were produced by mixing the ceramic and high density polyethylene particles using a single screw extrusion system. The results of the mechanical testing on the composite samples showed an increase in the fracture strength and the young's modulus values with increasing volume fraction of HA content in the composite samples. At the same time, there were decreases in both the fracture strain and toughness values with increasing volume fraction of the ceramic filler particles. In addition the comparison of the results obtained in this study with the mechanical properties of the commercially available composite samples (HAPEX) shows that similar mechanical properties can be reached at a much lower ceramic content, if nanoscaled HA particles are used in the fabrication of these composite biomaterials.     

Reactive processing of polyethylene and polyethylene–ethylene/propylene/dicyclopentadiene blends under static and dynamic conditions

Abstract

Dicumyl peroxide induced reactive melt processing of polyethylene (PE) in a shear mix at 170°C in the absence or presence of selected acrylic monomers (acrylic acid, ethyl acrylate, and butyl acrylate) has been studied. The acrylic graft copolymers of PE showed development of higher shear stress compared with the control PE when studied rheologically in a plate and cone viscometer at 160–190°C. All the modified PE products retained the pseudoplastic flow behaviour of PE. Measure of rupture shear parameters and of thixotropic and relaxation behaviour of the different modified PEs and of the control PE were also evaluated and compared. The observed effects and unexpected trends were analysed and interpreted.

The comparative effects of sulphur vulcanisation of polyethylene–ethylene/propylene/dicyclopentadiene terpolymer (PE–EPDM) blends by static and dynamic techniques were also studied using both a conventional curative system and a silane curative system. Rheometric studies indicated development of a co-continuous phase morphology for the 30/70 PE–EPDM blend. For a given blend, cured under given conditions, tensile strength and elongation at break at 25°C were higher for vulcanisates obtained statically than for those obtained dynamically, while the corresponding modulus values followed the opposite trend. The conventional curative usually cured at a higher rate. The property differences from static and dynamic vulcanisation are explained in the light of the differences in the developed morphology.     

PP-EPDM-NBR blends – The influence of added phenolic resin on processing and mechanical properties

Polypropylene (PP), ethylene-propylene-diene terpolymer (EPDM) and acrylonitrile rubber (NBR) in different proportions were mixed in a Haake Rheocord Mixer. To these mixtures phenolic resin was added in various concentrations, during processing, and the effects of this addition on processing and mechanical properties of the resulting blends were investigated. Received: 28 August 1997/Revised version: 3 November 1997/Accepted: 21 November 1997     

Effect of blend ratio on the dynamic mechanical and thermal degradation behavior of polymer–polymer composites from low density polyethylene and polyethylene terephthalate

Microfibrillar polymer–polymer composites (MFCs) based on low-density polyethylene (LDPE) and polyethylene terephthalate (PET) were prepared by cold drawing-isotropization technique. The weight percentage of PET was varied from 5 to 45 %. Microfibrils with uniform diameter distribution were obtained at 15 to 25 wt% of PET as evident from the scanning electron microscopy (SEM) results. Dynamic mechanical properties such as storage modulus (E′), loss modulus (E″) damping behavior (tan δ) were examined as a function of blend composition. The E′ values were found to be increasing up to 25 wt% of PET. An effort was made to model the storage modulus and damping characteristics of the MFCs using the classical equations used for short-fiber reinforced composites. The presence of PET microfibrils influenced the damping characteristics of the composite. The peak height at the β-transitions of loss modulus was lower for MFCs with 25 % PET, showing that they had superior damping characteristics. This phenomenon could be correlated with the PET microfibrils morphology. The thermal degradation characteristics of LDPE, neat blends and microfibrillar blends (MFBs) were compared. The determination of activation energy for thermal degradation was carried out using the Horowitz and Metzger method. The activation energy for thermal degradation of microfibrillar blends was found to be higher than that for the corresponding neat blends and MFCs. The long PET microfibrils present in MFBs could prevent the degradation and enhance the activation energy.     

Mechanical and thermal properties of copoly(styrene/acrylonitrile) compatibilised Nylon–thermoplastic elastomer blends

Abstract

The effects of blend compositions on the mechanical and thermal properties of polymer blends containing Nylon 66 and a thermoplastic elastomer (TPE), Santoprene^®, have been studied. A 5% styrene/acrylonitrile copolymer was added to neat Nylon, TPE, and their blends. The blends were injection moulded and the tensile and impact properties were investigated. The morphology and thermal properties of the blends were observed using scanning electron microscopy and differential scanning calorimetry.

The presence of double melting temperatures showed that the Nylon 66 and TPE are immiscible. However, blending produced a modification of mechanical and thermal properties. At TPE/Nylon ratios above 50 : 50 the tensile properties of TPE improved. In addition the impact properties of Nylon improved above the 50 : 50 ratio, i.e. in the TPE rich region. Both the melting temperature and crystallinity were depressed in the region of 50 : 50 blend composition. The presence of two phases, which is evidence of immiscibility of the blends, was confirmed by scanning electron microscopy.     

Adhesive properties of blends of phenol/cardanol–formaldehyde copolymer resin with polychloroprene rubber

This is a continuation of an earlier study on the adhesive properties of neoprene–phenolic resin blends. The phenolic resin used is derived from a mixture of phenol and cardanol, a renewable resource. Having established the utility of cardanol for formulating adhesives, this study investigates the effect of varying the phenol: cardanol ratio in the formulation. The effect of varying the total resin content at various phenol/cardanol ratios is also studied. It is found that a phenol/cardanol ratio of 80:20 is optimum for shear strength of aluminum–aluminum bonds, while a 60:40 ratio is the best for peel properties. For SBR–SBR and SBR–Al bonds, a 60:40 ratio is optimum for both peel as well as shear strength. Further, an 80 phr total resin content in the primer and a 40 phr resin content in the adhesive are found to give the best shear and peel strengths for SBR–Al bonds. The study reveals that the copolymer based on phenol, cardanol and formaldehyde is a better choice for the resin than either of the individual condensation products of phenol or cardanol with formaldehyde.     

Morphology and mechanical properties of nanostructured blends of epoxy resin with poly(?-caprolactone)-block-poly(butadiene-co-acrylonitrile)-block-poly(?-caprolactone) triblock copolymer

Poly(?-caprolactone)-block-poly(butadiene-co-acrylonitrile)-block-poly(?-caprolactone) triblock copolymer was synthesized via the ring-opening polymerization of ?-caprolactone with dihydroxyl-terminated butadiene-co-acrylonitrile random copolymer. The amphiphilic block copolymer was used to toughen epoxy thermosets via the formation of nanostructures. The morphology of the thermosets was investigated by means of atomic force microscopy, transmission electronic microscopy and small-angle X-ray scattering. It was judged that the formation of the nanostructures in the thermosets follows the mechanism of reaction-induced microphase separation. The thermal and mechanical properties of the nanostructured thermosets were compared to those of the ternary blends composed of epoxy, poly(butadiene-co-acrylonitrile) and poly(?-caprolactone) with the identical content of the modifiers. It is noted that at the same composition the nanostructured thermosets displayed higher glass transition temperatures (T_gs) than the ternary blends, which was evidenced by dynamic mechanical analysis. The fracture toughness of the thermosets was evaluated in terms of the measurement of critical stress field intensity factor (K_1C). It is noted that at the identical composition the nanostructured blends significantly displayed higher fracture toughness than the ternary blends. In addition, the K_1C of the nanostructured thermosets attained the maximum with the content of the modifier less than their counterpart of ternary blending.     

Influence of nano–micrometre powder blends on microstructure and mechanical properties of silicon nitride

Abstract

A well known route to making tough silicon nitride compositions is to control the grain size and aspect ratio distributions. This is usually done by choosing the appropriate powder characteristics, sintering conditions, as well as sintering additives. The effect of hot pressing a blend of nano and micrometre scale silicon nitride powder is explored here. Microstructures and mechanical properties are determined for these hot pressed ceramics and are compared with a reference silicon nitride. Hardness and fracture toughness are determined at room temperature using hardness indents produced by a macro Vickers hardness indenter. Grain size and aspect ratio distributions and their impact on mechanical properties are presented. Blending of nano and micrometre scale powder is shown to result in a refined microstructure with an increase in the area/volume fraction of finer grains. Rising R curves are established for these ceramics demonstrating toughening behaviour. Crack bridging and crack path deviation are identified as possible toughening mechanisms.     

Rheological and mechanical properties of polycarbonate–liquid-crystalline polymer blends with controlled chemical reactions

Chemical reactions can occur during the melt blending of polymers containing an ester group because ester groups are usually unstable at high temperatures; this instability generally deteriorates the mechanical properties of blends. Here, effects of chemical reactions on the rheological and mechanical properties of polycarbonate (PC)/liquid-crystalline polymer (LCP) blends are carefully investigated to determine a method for minimizing such undesirable impacts. For comparison, a physical blend, in which chemical reactions were minimized, was prepared at 300 °C in a twin-screw extruder. Both shear viscosity and complex viscosities of reactive blends were lower than those of physical blends, being almost proportional to [M_w ]^3.4 as a result of depolymerization and transesterification. Because of the enhanced miscibility, the tensile modulus of reactive blends increased compared with that of physical blend, according to the increase in the degree of incorporation (DI). It was also possible to increase tensile modulus if triester was added to the reactive blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2799–2807, 2001     

Investigation of polyethylene–wax blends by CRYSTAF and SEC–FTIR

Summary Oxidized wax blends with respectively HDPE, LDPE and LLDPE were investigated using CRYSTAF and SEC–FTIR in order to determine the possibility and extent of co–crystallization of the wax with each of these polyethylenes. CRYSTAF shows very little or no co–crystallization of wax with HDPE and LDPE, while there is a strong indication of co–crystallization in the case of LLDPE. SEC-FTIR analyses show co–elution of wax with LLDPE, indicating some chemical interaction between the oxidized wax and LLDPE.     

Thermo-mechanical properties of high density polyethylene – fumed silica nanocomposites: effect of filler surface area and treatment

High density polyethylene was melt compounded with various untreated (hydrophilic) or surface treated (hydrophobic) fumed silica nanoparticles, having different surface areas. The thermo-mechanical properties of the resulting nanocomposites have been thoroughly investigated. Field emission scanning electron microscopy revealed that nanofiller aggregation was more pronounced as the silica surface area increased, while nanofiller dispersion improved with a proper filler functionalization. The homogeneous distribution of fumed silica aggregates at low filler content allowed us to reach remarkable improvements of thermal stability, evidenced by an increase of the degradation temperature and a decrease of the mass loss rate with respect to neat matrix, especially when surface treated nanoparticles were utilized. Interestingly, the stabilizing effect produced by fumed silica nanoparticles was accompanied by noticeable enhancements of the ultimate tensile mechanical properties, both under quasi-static and impact conditions. Concurrently, a progressive enhancement of both elastic modulus and tensile stress at yield with the filler amount, was observed.     

Effects of vinyltrimethoxy silane on thermal properties and dynamic mechanical properties of polypropylene–wood flour composites

The viability of vinyltrimethoxy silane was investigated as a coupling agent for the manufacture of wood–plastic composites (WPC). The effect of silane pretreatment of the wood flour on the thermal and the dynamic mechanical properties and thermal degradation properties of the composites were studied. Moreover, the effect of organosilane on the properties of composites was compared with the effect of maleated polypropylene (MAPP). DSC studies indicated that the wood flour acts as a PP-nucleating agent, increasing the PP crystallization rate. In general, pretreatment with small amounts of silane improved this behavior in all the WPCs studied. Thermal degradation studies of the WPCs indicated that the presence of wood flour delayed degradation of the PP. Silane pretreatment of the wood flour augmented this effect, though without significantly affecting cellulose degradation. Studies of dynamic mechanical properties revealed that the wood flour (at up to 30 wt %) increased storage modulus values with respect to those of pure PP; in WPCs with a higher wood flour amount, there was no additional increase in storage modulus. Pretreatment of the wood flour with silane basically had no effect on the dynamic mechanical properties of the WPC. These results show that with small amounts of vinyltrimethoxy silane similar properties to the MAPP are reached. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Rheology, morphology and tensile properties of reactive compatibilized polyethylene/polystyrene blends via Friedel–Crafts alkylation reaction

Attempts were made to study the effect of reactive compatibilization via Friedel?CCrafts alkylation reaction, using AlCl₃ as a catalyst, on rheology, morphology, and mechanical properties of polyethylene/polystyrene (PE/PS) blends. The results of linear viscoelastic measurements in conjunction with the results of the mixing torque variation indicated that PS showed much more degradation than that of PE in the presence of AlCl₃. It was also found that while for PE-rich blends, the viscosity, and storage modulus increased by reactive compatibilization, they decreased for PS-rich blends. The variation of viscosity and storage modulus for 50/50 blend was found to be dependent on frequency ranges showing the competitive effects of PE?Cg?CPS copolymer formation and PS degradation. The results of morphological studies showed that reactive compatibilization decreased the particle size and particle-size distribution broadness because of in situ graft copolymer formation. Reactive compatibilization enhanced the tensile strength and elongation at break for PE-rich blends. It was demonstrated that there is a close interrelationship between rheology, morphology, and mechanical properties of reactive compatiblized PE/PS blends. It was also demonstrated that rheological behaviors have a reliable sensitivity to follow the structural and morphological changes during compatibilization process, so that, those information can be used to predict the morphology as well as mechanical properties of the blends.     

Effects of density and heat treatment of C/C preforms on microstructure and mechanical properties of C/C–SiC composites

Twill multidirectional carbon-fiber-reinforced carbon and silicon carbide composites (i.e., C/C–SiC) were prepared via chemical vapor infiltration combined with reactive melt infiltration process. The effect of heat treatment (HT) on the microstructure and mechanical properties of C/C–SiC composites obtained by C/C preforms with different densities was thoroughly investigated. The results show that as the bulk density of C/C preforms increases, the thickness of the pyrolytic carbon (PyC) layer increases and open pore size distribution narrows, making the bulk density and residual silicon content of C/C–SiC composites decrease. Moreover, the flexural strength and tensile strength of the C/C–SiC composites were improved, which can be attributed to the increased thickness of the PyC layer. The compressive strength reduces due to the decrease of the ceramic phase content. HT improves the graphitization degree of PyC, which reduces the silicon–carbon reaction rate and thereby the content of the SiC phase. HT induces microcracks and porosity but not obviously affects the mechanical properties of C/C–SiC composites. However, the negative impact of HT can be compensated by the increased density of the C/C preforms.     

Production and investigation of structure and properties of polyethylene–polylactide composites

Under conditions of shear deformations, low-density polyethylene (LDPE) and polylactide (PLA) composites are obtained in rotor disperser. The production of these composites allows one to use polymers derived from natural raw and to reduce the cost of the materials on their base. The addition of rigid PLA leads to increase in elastic modulus from 200 for LDPE to 1190 for LDPE–PLA (50:50 wt %) composites and in tensile strength from 13.3 for LDPE to 17.8 for LDPE–PLA. By differential scanning calorimetry method, it is shown that LDPE and PLA are incompatible. Using X-ray diffraction analysis, it is found that degree of crystallinity of composites decreases from 46.1 at 50:50 wt % to 36.9 at 80:20 wt % component ratios with the rise in LDPE content. Tests on fungus resistance show that the composites containing 50 wt % PLA are more resistant than the composites containing 30 wt % PLA. First by gel-permeation chromatography method, it is shown that composite degradation after exposure in soil is accompanied by the PLA chain scission and depolymerization with formation of monomers and dimers (M _w of PLA decreases from 118,860 to 80,100). The obtained composites can be applied as packaging materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47598.     

Study on gradient structure and interface mechanical properties of n–8YSZ/AlCoCrFeNi high–entropy coatings

In this study, gradient and double-layer coatings were prepared by atmospheric plasma spraying (APS) with nano ZrO₂–8%Y₂O₃(n–8YSZ)/AlCoCrFeNi high–entropy powder. The microhardness of the gradient coating changed in a manner consistent with the microstructure, and the average bond strength of the gradient coating was 2.50 times higher than that of the double-layer coating, indicating that the gradient structure of the coating can improve the sharp interface of the coating, and play a significant role in dispersion toughening to improve the bond strength of the coating. After 450 thermal cycles, the double-layer coating exhibited transverse propagation cracks accompanying coating spalling. In contrast, vertical cracks occurred inside the gradient coating, effectively increasing the coating strain tolerance and improving the coating life. Simultaneously, internal oxidation and cracks appeared in the substrate during cycles, the cracks were more obvious, and bridging occurred in the substrate of the double-layer coating, the substrate under the protection of the gradient coating produced microcracks that were discontinuous, indicating that the design of the gradient structure of the coating can effectively release the internal stress and improve the thermal shock resistance of the coating.     

Effects of electron beam irradiation on the structure–property behavior of blends based on low density polyethylene and styrene-ethylene-butylene-styrene-block copolymers

Low density polyethylene (LDPE) blends with different additives were exposed to various doses of electron beam irradiation. The additives used were styrene-ethylene-butylene-styrene-block copolymers (SEBS), styrene-ethylene-butylene-styrene-block copolymer grafted with maleic anhydride (SEBS-g-MA) and mineral compounds. The structure–property behavior of electron beam irradiated blends was characterized in terms of mechanical, thermal, and electrical resistivity properties. The results indicated that the unirradiated LDPE blends with the different compositions showed improved mechanical properties, thermal and volume resistivity properties than pure LDPE. However, the improvement in properties of unirradiated blends by using SEBS-g-MA was higher than using SEBS copolymer. Further improvement in the mechanical, thermal and electrical properties of the LDPE blends was achieved after electron beam irradiation. The limited oxygen index (LOI) data revealed that the LDPE/SEBS-g-MA/ATH blend was changed from combustible to self-extinguishing material after electron beam irradiation to a dose of 100 kGy. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012