Effects of filler–filler and polymer–filler interactions on rheological and mechanical properties of HDPE–wood composites

High‐density polyethylene (HDPE)–wood composite samples were prepared using a twin‐screw extruder. Improved filler–filler interaction was achieved by increasing the wood content, whereas improved polymer–filler interaction was obtained by adding the compatibilizer and increasing the melt index of HDPE, respectively. Then, effects of filler–filler and polymer–filler interactions on dynamic rheological and mechanical properties of the composites were investigated. The results demonstrated that enhanced filler–filler interaction induced the agglomeration of wood particles, which increased the storage modulus and complex viscosity of composites and decreased their tensile strength, elongation at break, and notched impact strength because of the stress concentration. Stronger polymer–filler interaction resulted in higher storage modulus and complex viscosity and increased the tensile and impact strengths due to good stress transfer. The main reasons for the results were analyzed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Analysis of the fluid–structure interaction in the optimization‐based design of polymer sheeting dies

A polymer‐sheeting‐die‐design methodology is presented that integrates a simulation of the polymer melt flow and die‐cavity deformation with numerical optimization to compute a die‐cavity geometry capable of giving a nearly uniform exit flow rate. Both the polymer melt flow and sheeting‐die deformation are analyzed with a general‐purpose finite‐element program. The approach includes a user‐defined element that is used to evaluate the purely viscous non‐Newtonian flow in a flat die. The flow analysis, which is simplified with the Hele–Shaw approximation, is coupled to a three‐dimensional finite‐element simulation for die deformation. In addition, shape optimization of a polymer sheeting die is performed by the incorporation of the coupled analyses in our constrained optimization algorithm. A sample problem is discussed to illustrate the die‐design methodology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3994–4004, 2007     

Fungal degradation of wood‐plastic composites and evaluation using dynamic mechanical analysis

Small samples of two wood–polyethylene (HDPE) composite formulations were incubated with either the white‐rot fungus Trametes versicolor or the brown‐rot fungus Gloeophyllum trabeum for 24 and 77 days in an agar‐block test. Noninoculated, side‐matched controls were employed in the tests to serve as references, and solid wood samples of yellow‐poplar (Liriodendron tulipifera L.) inoculated with T. versicolor were included as positive controls. Potential changes in storage and loss moduli because of fungal colonization and moisture were determined using dynamic mechanical analysis, whereas weight loss and visual observation served as indicators of fungal decay. Severe losses in storage modulus (E′) and loss modulus (E″) following incubation of yellow‐poplar with T. versicolor were observed. However, the E′ of the two wood–plastic composite (WPC) formulations increased after 24 days of incubation with T. versicolor. The same effect was observed for G. trabeum, but only in one formulation. The increase of E′ was attributed to a reinforcing effect of the fungal hyphae present in the interfacial gaps between the wood filler and the polymer matrix. Dynamic temperature scans revealed a peak in E″ between 30°C and 63°C, depending on the frequency and fungal treatment. The peak temperature of E″ represents the α‐transition of HDPE. Increased activation energies were required for the α‐transition in WPC samples incubated with T. versicolor for 77 days as compared to controls. This observation confirmed that incubation of WPC with T. versicolor improved interfacial adhesion and reinforced the composite under the assay conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3138–3146, 2006     

Use of titanate to improve interfacial interaction and mechanical properties of polyethylene/artificial marble wastes composites

The resource utilization of artificial marble wastes (AMWs) is urgently needed for environmental protection as a large amount of artificial marble are used as construction material. Nevertheless, it still remains challenging to achieve high performance of AMWs-filled polymer composites due to their poor interfacial interaction with hydrophobic polyolefins. Here, the unsaturated resin residue on the surface of AMWs is employed to construct strong interfacial interaction with high-density polyethylene (HDPE) matrix to prepare mechanically robust polymeric composites by use of titanate coupling agent. The mechanical properties (with a tensile strength of 28.6 MPa and a flexural strength of 27.7 MPa) of the resulting composites are comparable to or even better than those of raw calcium carbonate-filled HDPE composites. This work will not only promote the recycling and reutilization of AMWs, but also provide a feasible way for value-added application of other polymeric wastes, such as waste printed circuit board, waste artificial turf, and so on.     

The effect of matrix composition on the properties of cellulosic fibers–polyethylene composites

The solution/precipitation method was used for the preparation of polyethylene (PE)/cellulosic fibers composites. Blends of modified linear low density PE [linear low density PE‐grafted maleic anhydride (LLDPE‐g‐MAH)] with low density PE (LDPE) were used as matrices for the aforementioned composites. Blends of LDPE with a copolymer of LDPE and acrylic acid (AA)/n‐butyl acrylate (n‐BA) [(AA/n‐BA)–LDPE] were also studied for the same purpose. The reinforcing effect of cellulosic fibers in terms of tensile strength is more enhanced when mixtures of the modified polar polymer with pure PE were used as matrices, as compared with that corresponding to matrices consisting of modified PE alone. Regarding the Izod impact strength, composites of LLDPE‐g‐MAH presented the best performance with an improvement of 135% in comparison with specimens consisting of LDPE matrix, whereas composites of (AA/n‐BA)‐LDPE matrix showed a modest improvement of their impact resistance. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Structure and properties of polymer–wood composites based on an aliphatic copolyamide and secondary polyethylenes

Composite materials based on an aliphatic copolyamide and a secondary polyethylene, as thermoplastic matrices, and wood chips as filler were obtained and characterized. The influence of different factors (polymeric matrix type, fractional composition and geometrical characteristics of wood filler, processing parameters and ratio polymer/wood) on the properties of polymer–wood composites (PWCs) was studied. It was demonstrated that the packing factor F has an essential influence on the properties of PWCs: increasing F values determines an improvement in mechanical properties of these materials. Mechanical properties, thermal behaviour, morphological and diffusion characteristics of the analyzed composites were evaluated through specific methods and reported herein. Morphological and DSC data confirmed the presence of strong interface interactions between polymer and wood. The diffusion characteristics of PWCs showed that the diffusion coefficient D essentially depends on filler content in composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1700–1710, 2006     

Water absorption pattern and dimensional stability of oil palm fiber–linear low density polyethylene composites

The water absorption pattern and associated dimensional changes and solid loss of oil palm fiber–linear low density polyethylene composites was studied. The effects of fiber size (425–840, 177–425, and 75–177 μ), fiber loading (0, 10, 20, 30, 40, and 50%), and time of immersion (192 h at an interval of 24 h) on these parameters were also studied. Alkali treatment of fibers was done to reduce the hydrophilic nature of the composites and its effect was studied. It was found that the water absorption in most of the combinations followed typical Fickian behavior. The rate of water absorption and swelling increased with fiber loading. However, alkali treatment of the fibers resulted in a reduction of water absorption at higher fiber loadings only, and composites with higher fiber sizes exhibited higher water absorption. A sharp increase in the thickness swelling was observed in the initial days of immersion, which remained constant thereafter. The thickness swelling also increased with fiber size; however, a constant trend was not observed for the 75–177 μ fiber size. In addition to thickness swelling, composites also expanded linearly during water absorption; however, linear expansion was considerably less than thickness swelling. Higher fiber loading and alkali treatment caused more linear expansion. We observed that maximum solid loss on water immersion occurred with small‐sized and also alkali‐treated fiber composites. An increase in thickness and a decrease in linear dimension were observed after one sorption–desorption cycle. This irreversible change was also found to be proportional to fiber loading and alkali treatment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of irradiation crosslinking on the self‐heating and conduction of an acetylene carbon black filled high‐density polyethylene composite in the electric–thermal equilibrium state

The electric self‐heating and conduction behaviors of a high‐density polyethylene/acetylene carbon black composite crosslinked with electron‐beam irradiation are studied with respect to the electric field and ambient temperature. On the basis of scaling arguments, the critical fields and current densities for the onsets of self‐heating and global electrical breakdown are discussed with respect to the intrinsic resistivity at a given ambient temperature as well as the irradiation dosage. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Plasma treatment of wood–polymer composites: A comparison of three different discharge types and their effect on surface properties

Three different discharge types, based on the principle of a dielectric barrier discharge at atmospheric pressure, were investigated with regard to their influence on the adhesion properties of a series of wood–polymer composites. Wood flour (Picea abies L.) filled polypropylene and various proportions of polyethylene were manufactured either through extrusion or injection molding. The composites’ surfaces were activated by coplanar surface barrier discharge, remote plasma, and direct dielectric barrier discharge. The changes in wettability due to the pretreatment were investigated by contact angle measurement using the sessile drop method and calculation of surface free energy (SFE). It could be shown that wettability was improved by all three types of discharge, the contact angle decreased and the SFE correspondingly increased. X‐ray photoelectron spectroscopy revealed an increase in the O/C ratio at the material's surface. An improvement in coating adhesion was demonstrated by crosscut and pulloff tests. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43376.     

Effect of polyethylene‐graft‐maleic anhydride as a compatibilizer on the mechanical and tribological behaviors of ultrahigh‐molecular‐weight polyethylene/copper composites

Ultrahigh‐molecular‐weight polyethylene/copper (UHMWPE/Cu) composites compatibilized with polyethylene‐graft‐maleic anhydride (PE‐g‐MAH) were prepared by compression molding. The effects of the compatibilizer on the mechanical, thermal, and tribological properties of the UHMWPE/Cu composites were investigated. These properties of the composites were evaluated at various compositions, and worn steel surfaces and composite surfaces were examined with scanning electron microscopy and X‐ray photoelectron spectroscopy. The incorporation of PE‐g‐MAH reduced the melting points of the composites and increased their crystallinity to some extent. Moreover, the inclusion of the PE‐g‐MAH compatibilizer greatly increased the tensile rupture strength and tensile modulus of the composites, and this improved the wear resistance of the composites. These improvements in the mechanical and tribological behavior of the ultrahigh‐molecular‐weight‐polyethylene‐matrix composites with the PE‐g‐MAH compatibilizer could be closely related to the enhanced crosslinking function of the composites in the presence of the compatibilizer. Moreover, the compatibilizer had an effect on the transfer and oxidation behavior of the filler Cu particulates, which could be critical to the application of metallic‐particulate‐filled polymer composites in engineering. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 948–955, 2004     

Effects of ultraviolet absorbers on the ultraviolet degradation of rice‐hull/high‐density polyethylene composites

In China, rice‐hull powder is widely used as a fiber component to reinforce polymers because of its ready availability and lower cost compared to wood fibers. However, an issue concerning these composites is their weathering durability. In this study, the effects of two ultraviolet absorbers (UVAs), UV‐326 and UV‐531, on the durability of rice‐hull/high‐density polyethylene (HDPE) composites were evaluated after the samples were exposed to UV‐accelerated weathering tests for up to 2000 h. All of the samples showed significant fading and color changes in exposed areas. X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to detect surface chemical changes. The results indicate that surface oxidation commenced immediately within the first 500 h of exposure for all of the samples. However, the control rice‐hull/HDPE composites underwent a greater degree of oxidation than those with the UVAs. Scanning electron microscopy revealed that the rice‐hull/HDPE composites degraded significantly upon accelerated UV aging, with dense cracking on the exposed surface. The UVAs provided effective protection for the rice‐hull/HDPE composites, and UV‐326 had a more positive effect on the color stability than UV‐531. The results reported herein serve to enhance our understanding of the efficiency of UV stabilizers in the protection of rice‐hull/HDPE composites against UV radiation, with a view toward improving their formulation. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Photochemistry of low‐density polyethylene–montmorillonite composites

Photo‐oxidation at the exposed surfaces of low‐density polyethylene/montmorillonite composites was analyzed with attenuated total reflection/Fourier transform infrared spectroscopy. It was found that the clay particles were dispersed but not exfoliated in the polymer matrix. The extent of oxidative degradation of the low‐density polyethylene matrix was slightly greater when montmorillonite was present and was greatest for the blend of low‐density polyethylene and organically modified montmorillonite. The Fourier transform infrared measurements demonstrated that the rate of photo‐oxidation in the bulk was lower than that observed at the surface, but the oxidation chemistry was similar at the surface and in the bulk. The distribution of the photo‐oxidation products was somewhat modified in the presence of montmorillonite and organically modified montmorillonite in comparison with pure low‐density polyethylene, with the yield of acidic products higher and the yield of double bonds lower. These observations were attributed to a slightly higher yield of radicals and some modification of the quantum yield for the processes leading to the formation of double bonds when the clay filler was present. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Surface chemistry and mechanical property changes of wood‐flour/high‐density‐polyethylene composites after accelerated weathering

Although wood–plastic composites have become more accepted and used in recent years and are promoted as low‐maintenance, high‐durability building products, they do experience a color change and a loss in mechanical properties with accelerated weathering. In this study, we attempted to characterize the modulus‐of‐elasticity (MOE) loss of photostabilized high‐density polyethylene (HDPE) and composites of wood flour and high‐density polyethylene (WF/HDPE) with accelerated weathering. We then examined how weathering changed the surface chemistry of the composites and looked at whether or not the surface changes were related to the MOE loss. By examining surface chemistry changes, we hoped to begin to understand what caused the weathering changes. The materials were left unstabilized or were stabilized with either an ultraviolet absorber or pigment. After 1000 and 2000 h of accelerated weathering, the samples were tested for MOE loss. Fourier transform infrared (FTIR) spectroscopy was employed to monitor carbonyl and vinyl group formation at the surface. Changes in the HDPE crystallinity were also determined with FTIR techniques. It was determined that structural changes in the samples (carbonyl group formation, terminal vinyl group formation, and crystallinity changes) could not be reliably used to predict changes in MOE with a simple linear relationship. This indicated that the effects of crosslinking, chain scission, and crystallinity changes due to ultraviolet exposure and interfacial degradation due to moisture exposure were interrelated factors for the weathering of HDPE and WF/HDPE composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2263–2273, 2004     

Effects of coupling agents on the natural aging behavior and oxidation profile of high‐density polyethylene/sericite composites

The natural photooxidation of high‐density polyethylene (HDPE)/sericite composites was carried out outdoors for 180 days. The oxidative products, oxidation profile, and section morphology were characterized with Fourier transform infrared spectroscopy, infrared microscopy, and scanning electron microscopy, respectively. The results showed that HDPE/sericite had a higher oxidation degree than HDPE. All the coupling agents (CAs) accelerated the oxidation reaction of HDPE and made the final carbonyl index higher than that of an untreated one. The effect of sericite might have been due to the increased ultraviolet absorbance, whereas the effects of CAs might have been due to the active functional groups. Furthermore, cracks in the sections of test bars of HDPE/sericite composites after natural exposure were also observed. Their average lengths and densities were different for various CA treatments. This difference had a direct correspondence with the oxidation profile along the depth. This demonstrated that significant oxidation and consequently chain scission in the surface layer were responsible for the formation of cracks. Comparing the natural aging behavior of the films with test bars, we obtained more information about the propagation of the photooxidation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of three‐dimensional braided polyethylene fiber–PMMA composites and influence of fiber surface treatment

Three‐dimensional (3D) braided polyethylene (PE) fiber‐reinforced poly(methyl methacrylate) (PMMA), denoted as PE_3D/PMMA, composites were prepared. Mechanical properties including flexural and impact properties, and wear resistance were tested and compared with those of the corresponding unidirectional PE fiber–PMMA (abbreviated to PE_L/PMMA) composites. Both untreated and chromic acid‐treated PE fibers were used to fabricate the 3D composites in an attempt to assess the effect of chromic acid treatment on the mechanical properties of the composites. Relative changes of mechanical properties caused by fiber surface treatment were compared between the PE_3D/PMMA and PE_L/PMMA composites. The treated and untreated PE fibers were observed by scanning electron microscopy (SEM) and analyzed by X‐ray photoelectron spectroscope (XPS). SEM observations found that micro‐pits were created and that deeper and wider grooves were noted on the surfaces of the PE fibers. XPS analysis revealed that more hydroxyl (? OH) and carboxyl (? COOH) groups were formed after surface treatment. The physical and chemical changes on the surfaces of the PE fibers were responsible for the variations of the mechanical properties of the PE/PMMA composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 949–956, 2006     

Isothermal and nonisothermal crystallization of HDPE composites containing multilayer carton scraps as filler

The influence of multilayer carton scraps (MC) on crystallization kinetics of high-density polyethylene (HDPE) is detailed in this contribution. HDPE/MC composites were prepared by melt mixing, and a maleated linear low density polyethylene (MAPE) was added as compatibilizer. The crystallization kinetics of HDPE/MC/MAPE was analyzed as function of composition both in isothermal and nonisothermal conditions. The multilayer carton scraps appear to promote the onset of crystallization of HDPE, acting as efficient nucleating agent. The presence of MAPE as compatibilizer slightly reduces the nucleating efficiency of MC: the compatibilizer induces a delay in the onset of crystallization, caused by the need to exclude the bulky pendant groups of maleated linear low-density polyethylene from the crystals, as HDPE and MAPE chains cocrystallize. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites. I. Untreated fibers

The melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites was studied with an Instron capillary rheometer. The variation of melt viscosity with shear rate and shear stress at different temperatures was studied. The effect of relative composition of component fibers on the overall rheological behavior also was examined. A temperature range of 130 to 150°C and shear rate of 16.4 to 5470 s^?1 were chosen for the analysis. The melt viscosity of the hybrid composite increased with increase in the volume fraction of glass fibers and reached a maximum for the composite containing glass fiber alone. Also, experimental viscosity values of hybrid composites were in good agreement with the theoretical values calculated using the additive rule of hybrid mixtures, except at low volume fractions of glass fibers. Master curves were plotted by superpositioning shear stress and temperature results. The breakage of fibers during the extrusion process, estimated by optical microscopy, was higher for glass fiber than sisal fiber. The surface morphology of the extrudates was analyzed by optical and scanning electron microscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 432–442, 2003     

Effects of charge trapping on the electrical conductivity of low‐density Polyethylene–Carbon black composites

Electrical conductivities of low‐density polyethylene (LDPE)–carbon black (CB) composites were studied using high resistance meter at room temperature (DC conductivity) and dielectric spectroscopy (AC conductivity) in the frequency range between 90 kHz and 13 MHz and temperature range from 120 to 355 K. DC measurements revealed a percolation threshold at about 20 wt % of CB content, whereas AC measurements show two conductivity peaks at about 15% and 23% of CB content. The presence of two percolation thresholds was attributed to different dispersions of CB particles in structural inhomogeneities of LDPE. The experimental data were analyzed using the model of Efros and Shklovskii, which describes the critical behavior of a complex conductivity using critical indexes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of polyurethane sizing agent on interface properties of carbon fiber reinforced polycarbonate composites

This work is aimed at investigating how molecule structure of polyurethanes (PUs) as sizing agents influence the interface properties of carbon fiber (CF) reinforced polycarbonate (PC) composites. Effects of four PUs as sizing agents for CF on the interlaminar shear strength (ILSS) of CF reinforced PC composites are investigated. It is found that the three PUs except PC–PU as sizing agents on oxidized CF (OCF) made the ILSS of their reinforced PC composites increase up to 62.9 MPa by more than 24.8%. The chemical interaction between PU sizing agents and CF are attributed to high reactivity of isocyanate, but carbonate groups on PC–PU may have a chain unzipping reaction due to active groups on the surface of OCF. The chemical interaction between PU sizing agents and PC are attributed to transesterification. As a result, PUs containing isocyanate or polyester groups are ideal sizing agents for CF reinforced PC composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47982.     

Phase structural analyses of polyethylene extrusion coatings on high‐density papers. II. Influence of paper surface properties on the polyethylene morphology

Paper samples of three different qualities were extrusion coated with low‐density polyethylene (LDPE) and high‐density polyethylene (HDPE). The morphological phases of the polyethylene layers have been quantified by ¹³C solid‐state high‐resolution NMR. Shear forces in the process initiate the formation of the monoclinic crystallites. The surface tensions of the high‐density papers have influence on the degree of interaction between the two materials and how these shear forces work. The paper surface properties will thus have an influence on properties and the size of the monoclinic crystalline mass fraction of the polyethylene coating. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 226–234, 2004