Wood‐thermoplastic composites from wood flour and high‐density polyethylene

High‐density polyethylene/wood flour (HDPE/WF) composites were prepared by a twin‐screw extruder. The effects of WF, silane coupling agents, polymer compatibilizers, and their content on the comprehensive properties of the WF/HDPE composites have been studied in detail, including the mechanical, thermal, and rheological properties and microstructure. The results showed that both silane coupling agents and polymer compatibilizers could improve the interfacial adhesion between WF and HDPE, and further improve the properties of WF/HDPE composites, especially with AX8900 as a compatibilizer giving higher impact strength, and with HDPE‐g‐MAH as a compatibilizer giving the best tensile and flexural properties. The resultant composite has higher strength (tensile strength = 51.03 MPa) and better heat deflection temperature (63.1°C). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Impedance spectra of carbon black filled high‐density polyethylene composites

Carbon black (CB) filled high‐density polyethylene (HDPE) composites are prepared by ordinary blending for use as an electrical conductive polymer composite. The composite changes from an electrical insulator to a conductor as the CB content is increased from 10 to 20 wt %, which is called the percolation region. For explanatory purposes, three models, namely, “conduction via nonohmic contacting chain,” “conduction via ohmic contacting chain,” and a mixture of them corresponding to the conductions in the percolation region, high CB loading region, and limiting high CB loading are proposed by the reasonable configurations of aggregate resistance, contact resistance, gap capacitance, and joining aggregates induction. The characters of the impedance spectra based on the three models are theoretically analyzed. In order to find some link between the electrical conductivity and the CB dispersion manner in the composites, the impedance spectra of three samples, HDPE/15 wt % CB (the center of the percolation region), HDPE/25 wt % CB (a typical point in the high CB loading region), and HDPE/19 wt % CB (the limiting high CB loading region), are measured by plotting the impedance modulus and phase angle against the frequency and by drawing the Cole–Cole circle of the imaginary part and real part of the impedance modulus of each sample. The modeled approached spectra and the spectra measured on the three samples are compared and the following results are found: the measured impedance spectrum of HDPE/15 wt % CB (percolation region) is quite close to the model of conduction via nonohmic contacting chain. The character of the measured spectrum of HDPE/25 wt % CB consists of the form of the model of conduction via ohmic contacting chain. The impedance behavior of HDPE/19 wt % CB exhibits a mixture of the two models. From the comparisons, it is concluded that the electrical conducting network in the percolation region of the CB filled HDPE composite is composed of aggregate resistance, nonohmic contact resistance, and gap capacitance, and that of the high CB loading region consists of continuously joined CB aggregate chains, which are possibly wound and assume helix‐like (not straight lines) conductive chains, acting as electrical inductions as the current passes through. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1344–1350, 2005     

Electrical resistivity of carbon black filled high‐density polyethylene composites

The electrical resistivity of high‐density polyethylene (HDPE) loaded with carbon black (CB) blends was evaluated as a function of the blending time and the melt index of HDPE. The relationship between the positive temperature coefficient effect and the room temperature volume resistivity was investigated. The positive temperature coefficient effect and reproducibility were improved significantly when the blending time of HDPE and CB was comparatively long. The effects of ⁶⁰Co γ‐ray and electron beam irradiation on the positive and negative temperature coefficient behavior of the blends were studied. The effect of thermal aging on the volume resistivity was studied to ascertain the structural stability. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2440–2446, 2002     

Mechanical and thermal properties of low density polyethylene composites filled with dye‐loaded shell powder

To achieve reinforcement and coloring in one combined process of polymer production, a dye‐loaded shell powder (DPSP) based on Congo red and pearl shell powder was prepared and used as a versatile bio‐filler in low‐density polyethylene (LDPE). The DPSP was characterized by means of X‐ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. The mechanical, thermal, and colorimetric properties of prepared LDPE/DPSP composites were investigated as well. Adding DPSP could significantly increase the strength and stiffness of LDPE composites while giving an outstanding coloring performance. Moreover, the impact strength of LDPE composites was improved at lower filler loading rate, and the maximum incorporation content could reach 10 wt % with a good balance between toughness and stiffness of LDPE composites. The thermal performance studies confirmed an increase in thermal stability and heat resistance of LDPE composites with the incorporation of DPSP. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44118.     

Ultraviolet weathering of photostabilized wood‐flour‐filled high‐density polyethylene composites

Wood‐plastic composites are being increasingly examined for nonstructural or semistructural building applications. As outdoor applications become more widespread, durability becomes an issue. Ultraviolet exposure can lead to photodegradation, which results in a change in appearance and/or mechanical properties. Photodegradation can be slowed through the addition of photostabilizers. In this study, we examined the performance of wood flour/high‐density polyethylene composites after accelerated weathering. Two 2⁴ factorial experimental designs were used to determine the effects of two hindered amine light stabilizers, an ultraviolet absorber, a colorant, and their interactions on the photostabilization of high‐density polyethyl‐ ene blends and wood flour/high‐density polyethylene composites. Color change and flexural properties were determined after 250, 500, 1000, and 2000 h of accelerated weathering. The results indicate that both the colorant and ultraviolet absorber were more effective photostabilizers for wood flour/high‐density polyethylene composites than the hindered amine light stabilizers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2609–2617, 2003     

Resistivity relaxation behavior of carbon black filled high‐density polyethylene conductive composites

The variation of resistivity for high‐density polyethylene (HDPE) conductive composites filled with carbon black (CB) with time was investigated under the excitation of different temperature field. The movement of CB particles in the HDPE matrix was not a momentary equilibrium process, but a relaxation process. The relaxation of resistivity of the composites was monotonic, and it could be described by an exponential form above melting temperature. However, the relaxation of resistivity was nonmonotonic below melting temperature, herein a parameter t₀ which was the beginning time of the resistivity attenuation could be introduced into the exponential equation. The attenuation of resistivity at constant temperature was limited for the composites with certain content of CB. The resistivity of the composites would incline to a constant value with the prolongation of time no matter what the heat treatment temperature was. Heating rate had influence on the relaxation of resistivity of the composites, and the lower heating velocity resulted in less time to approach to the equilibrium resistivity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of vinylsilane crosslinked high‐density polyethylene composites filled with nanoclays

High‐density polyethylene (HDPE) treated with various vinyltriethoxysilane (VTES) contents and filled with different Cloisite 15A contents were investigated. VTES was used to improve the HDPE‐clay interaction. The morphology and extent of crosslinking, as well as the thermal, mechanical, and thermomechanical properties were studied. X‐ray diffraction (XRD) results of the treated HDPE/clay nanocomposites showed an increase in interlayer spacing, which indicates that the polymer chains were intercalated between the clay layers. Transmission electron microscopy micrographs showed some evidence of exfoliated clay layers, indicating that the system exhibited a mixed morphology. The clay containing samples had a better thermal stability than HDPE, but the thermal stability did not differ much with increasing clay loading. VTES observably decreased the melting enthalpy of HDPE, while the presence of clay had little influence on this value. This is somewhat contrary to the gel content results, which showed a decrease in the extent of crosslinking in the presence of clay and with increasing clay content. VTES treatment and the presence of clay observably changed the dynamic mechanical and tensile behavior of the HDPE. POLYM. COMPOS., 34:1720–1727, 2013. © 2013 Society of Plastics Engineers     

Physical,mechanical, and thermal properties of polypropylene composites filled with walnut shell flour

Injection molded specimens were prepared from the walnut shell flour and polypropylene with and without maleic anhydride-grafted polypropylene at 40, 50, and 60% (weight) contents of the walnut shell. The bending and tensile modulus of the composites significantly increased with increasing the filler content while the bending and tensile strengths significantly decreased. Water absorption and thickness swelling of the composites increased with increasing filler content. The MAPP improved the interfacial adhesion between walnut shell flour and polymer matrix. A 40/57/3 formulation of the walnut shell flour/polypropylene/MAPP can be used in outdoor applications requiring a high dimensional stability.     

Electric self‐heating behavior of acetylene carbon black filled high‐density polyethylene composites

The electric self‐heating behavior of carbon black (CB) filled high‐density polyethylene (HDPE) was studied in relation to the time‐dependent current and surface temperature under various voltages and to the voltage‐dependent surface temperature at electric–thermal equilibrium. The resistance increase due to self‐heating restricts the current flow through the sample and thus stabilizes the electric power and the self‐heating temperature to their saturation values, which vary with the voltage. A simple phenomenological model shows that self‐heating at electric‐thermal equilibrium is involved in the initial resistance, the electric field induced positive temperature coefficient (PTC) transition and the heat dissipation. The influences of annealing and irradiation crosslinking on the self‐heating behavior are discussed. Copyright © 2004 Society of Chemical Industry     

Tensile deformation and fracture mechanism of highly filled high‐density polyethylene/Al(OH)3 composites

The effect of the silicone oil content on the tensile properties and micromechanical deformation of high‐density polyethylene/Al(OH)₃ composites was studied. With an increase in the silicone oil content, the elongation at break and notched Izod impact strength of the composites increased, and the local debonding deformation gradually transformed into homogeneous debonding deformation. A model characterizing the micromechanical deformation process was examined. The increase in the silicone oil content decreased the interaction between the filler particles and the high‐density polyethylene matrix and increased the extension speed of the debonded region, which led to the changes in the tensile properties and micromechanical deformation. A good explanation for the tensile properties and micromechanical deformation was obtained through the model. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1207–1218, 2002     

Effect of compatibilizing agents on the mechanical properties of high‐density polyethylene/olive husk flour composites

The main objective of this research was to investigate the effect on the thermal and mechanical properties of the addition of two different compatibilizing agents, malefic anhydride‐grafted polyethylene (PE) [synthesized in a solution state (MAPE) and commercial (XA255)], to olive husk flour, high‐density polyethylene (HDPE) composites. The composites contain 30 wt % of olive husk flour and a variable proportion of compatibilizer (3, 5, and 7 wt %). The grafting reaction was followed by Fourier transform infrared, and the grafting degree was evaluated by means of titration. The effect of grafting on the thermal properties of MAPE was observed by ATG/DTG. The mechanical and thermal properties of the composite were investigated. A morphological study of the composite reveals that there is a positive effect of compatibilizing agent on interfacial bonding. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical properties of low nano‐silica filled high density polyethylene composites

Modification of nanoparticles through graft polymerization is able to change the chemical nature of the particles' surfaces and provides an effective means for the preparation of nano‐fillers specified for composites manufacturing. The present work focuses on the mechanical role of grafted nano‐SiO₂ particles in high density polyethylene composites prepared by melt compounding. The experimental results show that at a content of 0.75 vol%, the modified nano‐silica results in a rise in tensile stiffness, tensile strength and impact strength of the composites. The grafted nanoparticles can improve the mechanical performance of the matrix polymer more effectively than the untreated version. In addition, a further enhancement of the composites stiffness and strength can be achieved by crosslinking the concentrated masterbatches, which has not yet been revealed in the authors' previous works on grafted nano‐SiO₂ particles/polypropylene composites. It is thus revealed that the introduction of the grafting polymers onto the nanoparticles increases the tailorability of the composites.     

Effect of recycled polypropylene on polypropylene/high‐density polyethylene blends

The effect of recycled PP on incompatible blends of virgin polypropylene (PP) and high‐density polyethylene (HDPE) was studied. Recycled PP from urban solid waste was extracted with methyl ethyl ketone and the compatibilizing action of the product before and after extraction was examined. The characterization of the recycled PP was performed by FTIR, NMR, and DSC analyses. Mechanical properties of the blends were evaluated. The results showed partial compatibility of the blend components, reflected in the improvement of the tensile strength and elongation. Best results were achieved by the addition of extracted recycled PP on the 50/50 PP/HDPE blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1305–1311, 2001     

Comparative mechanical,fire‐retarding,and morphological properties of high‐density polyethylene/(wood flour) composites with different flame retardants

Aluminum hydroxide, magnesium hydroxide, and 1,2‐bis(pentabromophenyl) ethane were incorporated into high‐density polyethylene (HDPE) and wood flour composites, and their mechanical properties, morphology, and fire‐retardancy performance were characterized. The addition of flame retardants slightly reduced the modulus of elasticity and modulus of rupture of composites. Morphology characterization showed reduced interfacial adhesion among wood flour, HDPE, and flame retardants in the composites compared with control composites (HDPE and wood flour composites without the addition of flame retardants). The flame retardancy of composites was improved with the addition of the flame retardants, magnesium hydroxide and 1,2‐bis(pentabromophenyl) ethane, especially 1,2‐bis(pentabromophenyl) ethane, with a significant decrease in the heat release rate and total heat release. Char residue composition and morphology, analyzed by attenuated total reflectance, Fourier‐transform infrared spectroscopy, and scanning electron microscopy, showed that the char layer was formed on the composite surface with the addition of flame retardants, which promoted the fire performance of composites. The composites with 10 wt% 1,2‐bis(pentabromophenyl) ethane had good fire performance with a continuous and compact char layer on the composite surface. J. VINYL ADDIT. TECHNOL., 24:3–12, 2018. © 2015 Society of Plastics Engineers     

Effect of surface treatment on the physicomechanical and thermal properties of high‐density polyethylene/olive husk flour composites

In this study, a particular interest was focused on the recovery of lignocellulosic waste of olive husk flour (OHF) by its incorporation as filler in manufacturing composite materials based on high‐density polyethylene (HDPE) matrix with various filler contents (10, 20, and 30 wt %). The problem of incompatibility between the hydrophilic filler and the hydrophobic matrix was treated with two methods: the first method consists of using maleic anhydride‐grafted polyethylene (MAPE) as compatibilizer in HDPE/OHF composites. The second method, was focused on the chemical modification of OHF by vinyl‐triacetoxy‐silane (VTAS). Fourier transform infrared spectroscopy is used to analyze both grafting and silanization reactions involved. Scanning electron microscopy was used to show the morphology of the flour surface. Furthermore, the physicomechanical and thermal characteristics of the various composite samples were investigated as a function of filler contents and treatment types. The results showed that the properties of the composite materials are positively affected by the silanization treatment of OHF and also by MAPE addition. However, better mechanical and thermal properties with less moisture absorption were obtained for the composite materials compatibilized with MAPE. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Wood–high‐density polyethylene composites: Water absorption and mechanical properties

In this research, the effect of water absorption on the mechanical properties of wood/high‐density polyethylene (HDPE) composites were investigated. HDPE (44005ARPC) was used as the polymer matrix, and spruce sawdust was used as the filler at a maximum loading of 50 wt % of the total weight of each compound. All compounds contained 5 wt % magnesium stearate as a lubricant and 0.5 wt % Irgafos 168 as a heat stabilizer. Four factors in two levels were chosen [talc (filler) at levels of 5 and 15 wt %, zinc borate (fungicide) at levels of 0 and 1 wt %, maleic anhydride polyethylene (coupling agent) at levels of 4 and 6 wt %, and method of mixing (one‐step vs. two‐step mixing)], and eight compounds were prepared with an L8 Taguchi orthogonal array which has 8 combinations of levels. The effects of each factor at two levels on the diffusion constant and the tensile and bending strengths (under wet and dry conditions) were investigated by the analysis of variance of means with 90% confidence. The optimum level for each factor is reported. The results show that there was a linear correlation between the diffusion constant and tensile and bending strengths when the samples were immersed in distilled water. A higher diffusion constant resulted in much lower tensile and bending strengths with immersion in distilled water until saturation was reached. Scanning electron microscopy images confirmed good mixing when two‐steps mixing was used. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of high‐energy vibro‐milling of filler on the mechanical properties of filled high‐density polyethylene

The effect of high‐energy mechanical milling of CaCO₃ (calcium carbonate) and STC (a mixture of sericite, tridymite and cristobalite) on mechanical properties, rheological and dynamical mechanical behavior of high‐density polyethylene (HDPE)/CaCO₃ and HDPE/STC was studied through SEM (scanning electron microscope), DMTA (dynastic mechanical test analysis), mechanical and melt rheological properties tests. The experimental results show that addition of fillers treated by coupling agent and vibromilling to HDPE makes the impact strength of HDPE greatly increased. The impact strength of HDPE/treated CaCO₃ (60/40) and HDPE/treated STC (60/40) is ca. 4 and 3 times respectively as high as that of HDPE. The SEM micrographs of impact fractured surfaces of treated fillers filled HDPE show extensive plastic deformation of HDPE matrix, indicating that the plastic deformation of matrix induced by the treated fillers is the main contribution for absorbing a great amount of impact energy. This is the reason why the impact strength of HDPE greatly increases with addition of coupling agent and vibromilling treated fillers. The intensity of γ relaxation peak of HDPE in HDPE/treated CaCO₃ on tanδ vs. temperature curve increases and the peak shifts to higher temperature due to its stronger interface interaction as compared with that of HDPE/untreated CaCO₃.     

A preliminary study on mechanical‐electrical behavior of graphite powder‐filled high‐density polyethylene composites

Mechanical and electrical responses of graphite powder (GP)‐filled high‐density polyethylene composites to a uniaxial compression–decompression cycle were studied. Above a compression loading level, a large positive‐pressure coefficient effect of resistance was observed, for which a slide mechanism of GP in the matrix is believed to be responsible. In a step‐wise compressive loading and loading‐holding experiment, the critical compression level was also found, at which the resistance response changed from a time‐independent one to a time‐dependent, creep‐like one. The current‐voltage behavior of the composites showed that the GP contact was non‐ohmic, regardless of GP contents and pressure levels. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 792–796, 2000     

Rheological behavior of high‐density polyethylene (HDPE) filled with paper mill sludge

A comparative study was conducted of composites made with sludge from three different paper mills. Sludges were obtained from a thermomechanical pulp (TMP), a chemico‐TMP (CTMP), and a Kraft mill with a feedstock of primarily black spruce. The primary sludge (PS) and secondary sludge (SS) were mixed at two different ratios (PS:SS = 7:3 and 9:1) and blended with high‐density polyethylene (HDPE) at 20%, 30%, and 40% proportion. The blends were tested using plate–plate geometry before subjection to frequency sweep by oscillation rheometry. The storage modulus (G′), loss modulus (G″), and complex viscosity (η*) increased with increasing paper sludge content. Decreasing the PS:SS ratio from 9:1 to 7:3 decreased G′, G″, and η*. Differential scanning calorimetry showed that sludge addition increased both the melting and crystallization temperature, for a positive effect on crystallinity. Although the behavior of sludge–high‐density polyethylene blends differed from that of traditional wood plastic composite made with wood flour, they obtained G′, G″, and η* values of the same magnitude. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46484.     

Time dependences of conduction and self‐heating in acetylene carbon black‐filled high‐density polyethylene composites

The time dependences of electrical conduction and self‐heating behaviors in high‐density polyethylene filled with acetylene carbon black of 0.082 in volume fraction are studied in relation to voltage and ambient temperature. The characteristic decay current constant τ_i, and the exponential growth time constant for self‐heating τ_g are determined for the samples under voltages U above the critical value U_c for the onset of self‐heating. The influences of voltage and ambient temperature on τ_i and τ_g as well as the amplitude of the low‐resistance to high‐resistance switching are discussed on the basis of the random resistor network (RRN) model and the relationship between U_c and the intrinsic resistivity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1124–1131, 2006