Structure and properties of phase‐change materials based on high‐density polyethylene,hard Fischer–Tropsch paraffin wax,and wood flour

Phase‐change materials based on high‐density polyethylene (HDPE), a hard Fischer–Tropsch paraffin wax (H1 wax), and alkali‐treated wood flour (WF) were investigated. The blends and composites were prepared by melt‐mixing. They were characterized in terms of their morphology as well as thermal, mechanical, thermomechanical, and water absorption properties. Although the scanning electron microscopy micrographs showed some evidence of intimate contact between WF and the HDPE matrix, there were poor filler dispersion and interfacial adhesion. The percentage miscibility of H1 wax in HDPE seems to have decreased with increasing wax content in the blends. A fairly strong affinity between the WF and H1 wax was noticed. There was plasticization of the HDPE matrix by the wax as well as inhomogeneity and uneven wax dispersion within the polymer matrix. The presence of H1 wax and WF influenced the crystallization behavior of the HDPE matrix. The incorporation of wax reduced the thermal stability of the blends and composites, but stabilized the WF. The H1 wax and WF differently influenced the viscoelastic properties of the HDPE matrix. In contrast to the blends where the tensile properties improved in the presence of wax, the composites showed poorer properties. An increase in wax content resulted in a decrease in water uptake by the composites. POLYM. COMPOS., © 2011 Society of Plastics Engineers.     

Rheological behavior and mechanical properties of wood flour/high density polyethylene blends: Effects of esterification of wood with citric acid

This study explored the modifying effects of wood flour (WF) with citric acid (CA) on the rheological and mechanical properties of WF/high density polypropylene (HDPE) composites. WF was treated with CA, which acts a cross‐linking agent and melt‐blended with HDPE with a twin‐screw extruder. Injection molding was used to make tensile and impact tests samples. The rheological properties of the blends were characterized using a Haake microcompounder, torque‐, capillary‐, and rotational‐rheometer, respectively. Results show that the thermal stability of WF decreased after treatment. Compared with those of untreated composites, the tensile strength, elongation‐at‐break, and impact strength of the composites treated with 5% CA were reduced by 6%, 14%, and 16%, respectively. This reduction was attributed to embrittlement of WF, which may negatively influence the mechanical properties of the resulting composites. Scanning electron microscopy revealed better dispersion of CA‐treated WF in the composites than the untreated WF. For composites treated with 5% CA, the melt torque, viscosity, moduli, and shear stress decreased significantly, indicating an improvement in processibility. This improvement is attributed to uniform dispersion of the modified WF, as well as to better interfacial adhesion between WF and the matrix. Results suggest that treating WF with CA shows promise for improving the processibility of highly filled thermoplastic composites via extrusion/injection molding processing. POLYM. COMPOS., 37:553–560, 2016. © 2014 Society of Plastics Engineers     

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     

Viscoelastic,thermal, and morphological analysis of HDPE/EVA/CaCO<Subscript>3</Subscript> ternary blends

High density polyethylene (HDPE), calcium carbonate (CaCO₃), and ethylene vinyl acetate (EVA) ternary reinforced blends were prepared by melt blend technique using a twin screw extruder. The thermal properties of these prepared ternary blends were investigated by differential scanning calorimetry. The effect of EVA loading on the melting temperature (T _m) and the crystallization temperature (T _C) was evaluated. It was found that the expected heterogeneous nucleating effect of CaCO₃ was hindered due to the presence of EVA. The melt viscosities of the ternary reinforced blends were affected by the % loading of CaCO₃, EVA, and vinyl acetate content. Viscoelastic analysis showed that there is a reduction of the storage modulus (G′) with increasing of EVA loading as compared to neat HDPE resin or to HDPE/CACO₃ blends only. The morphology of the composites was characterized by scanning electron microscopy (SEM). The dispersion and interfacial interaction between CaCO₃ with EVA and HDPE matrix were also investigated by SEM. We observed two main types of phase structures; encapsulation of the CaCO₃ by EVA and separate dispersion of the phases. Other properties of ternary HDPE/CaCO₃/EVA reinforced blends were investigated as well using thermal, rheological, and viscoelastic techniques.     

Synergistic compatibilization and reinforcement of HDPE/wood flour composites

Multi‐monomer grafted copolymers, high‐density polyethylene‐grafted‐maleic anhydride‐styrene (HDPE‐g‐(MAH‐St)) and polyethylene wax‐grafted‐ maleic anhydride ((PE wax)‐g‐MAH), were synthesized and applied to prepare high‐performance high‐density polyethylene (HDPE)/wood flour (WF) composites. Interfacial synergistic compatibilization was studied via the coordinated blending of high‐density polyethylene‐grafted‐maleic anhydride (MPE‐St) and polyethylene wax‐grafted‐ maleic anhydride (MPW) in the high‐density polyethylene (HDPE)/wood flour (WF) composites. Scanning electron microscopy (SEM) morphology and three‐dimensional WF sketch presented that strong interactive interface between HDPE and WF, formed by MPE‐St with high graft degree of maleic anhydride (MAH) together with the permeating effect of MPW with a low molecular weight. Experimental results demonstrated that HDPE/WF composites compatibilized by MPE‐St/MPW compounds showed significant improvement in mechanical properties, rheological properties, and water resistance than those compatibilized by MPE, MPE‐St or MPW separately and the uncompatibilized composites. The mass ratio of MPE‐St/MPW for optimizing the HDPE/WF composites was 5:1. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42958.     

The effects of clay dispersion on the mechanical,physical, and flame‐retarding properties of wood fiber/polyethylene/clay nanocomposites

In this study, nanosized clay particles were introduced into wood fiber/plastic composites (WPCs) to improve their mechanical properties and flame retardancy, which are especially important in various automotive and construction applications. A high degree of exfoliation for nanoclay in the wood fiber/high density polyethylene (HDPE) composites was successfully achieved with the aid of maleated HDPE (PE‐g‐MAn), through a melt blending masterbatch process. The structures and morphologies of the composites were determined using X‐ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. This article presents the effects of clay content and degree of clay dispersion on the mechanical and physical properties and flame retardancy of wood fiber/HDPE composites that contained a small amount of clay, in the range of 3–5 wt %. We concluded that achieving a higher degree of dispersion for the nanosized clay particles is critical to enhance the mechanical properties and the flame retardancy of WPCs when small amounts of clay are used. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical properties and morphology of the modified HDPE/starch reactive blend

We investigated the effect of reactive blending on the mechanical properties and morphology of high‐density polyethylene (HDPE)/plasticized starch blends. HDPE was chemically modified to enhance the compatibility with the plasticized starch. The modified HDPE, HDPE‐g‐glycidyl methacrylate (GMA), was synthesized by melt reaction of HDPE in the presence of dicumyl peroxide (DCP). A finer dispersion of starch in the HDPE matrix was achieved compared to that in the unmodified HDPE. The amount of GMA groups in the modified HDPE enhanced the miscibility of HDPE/starch blends. We also observed that the amount of glycerin improves the mechanical properties of blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3313–3320, 2001     

Effect of interfacial stress on the crystalline structure of the matrix and the mechanical properties of high‐density polyethylene/CaCO3 blends

A series of high‐density polyethylene (HDPE)/CaCO₃ blends were prepared with different kinds of coupling agents, with CaCO₃ particles of different sizes, and with matrixes of different molecular weights during the melt‐mixing of HDPE and CaCO₃ particles. The mechanical properties of these blends and their dependence on the interfacial adhesion and matrix crystalline structure were studied. The results showed that the Charpy notched impact strength of these blends could be significantly improved with an increase in the interfacial adhesion or matrix molecular weight or a decrease in the CaCO₃ particle size. When a CaCO₃ surface was treated with a compounded coupling agent, the impact strength of the HDPE/CaCO₃(60/40) blend was 62.0 kJ/m², 2.3 times higher than that of unimproved HDPE; its Young's modulus was 2070 MPa, 1.07 times higher than that of unimproved HDPE. The heat distortion temperature of this blend was also obviously improved. The improvement of the mechanical properties and the occurrence of the brittle–tough transition of these blends were the results of a crystallization effect induced by the interfacial stress. When the interfacial adhesion was higher and the CaCO₃ content was greater than 30%, the interfacial stress produced from matrix shrinkage in the blend molding process could strain‐induce crystallization of the matrix, leading to an increase in the matrix crystallinity and the formation of an extended‐chain (or microfibrillar) crystal network. The increase in the critical ligament thickness with an increasing matrix molecular weight was attributed to the strain‐induced areas becoming wider, the extended‐chain crystal layers becoming thicker, and the interparticle distance that formed the extended‐chain crystal network structure becoming larger with a higher matrix molecular weight. The formation of the extended‐chain crystal network and the increase in the matrix crystallinity were also the main reasons that Young's modulus and the heat distortion temperature of this blend were improved. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2120–2129, 2003     

The effect of paraffin on fiber dispersion and mechanical properties of polyolefin–sawdust composites

This article reports on the influence of the paraffin (PAR) on the wood fiber (WF) dispersion in different polyethylene (low‐density polyethylene, high‐density polyethylene, recycled polyethylene) matrices, as well as on the melt flow behavior and mechanical properties of WF‐reinforced polyethylene (PE) composites. In the presence of paraffin, the composites showed improved tensile and flexural strength and modulus, but lower impact strength and elongation at break. The extent of improvement in mechanical properties depends on paraffin content and type of polyethylene; the most effective paraffin was in LDPE‐based composites. Paraffin‐treated WF showed lower moisture absorption ability in comparison with unmodified wood fiber. The phase segregation process was investigated for PE/PAR blends by DSC method. It was shown that an increase of paraffin concentration in the PE/PAR blend leads to a decrease of PE melting temperature and an increase of paraffin melting temperature; it indicates a net exchange of material from paraffin towards polyethylene. However, generally both components of PE/PAR blends remain immiscible. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2385–2393, 2004     

Processability,morphology and mechanical properties of wood flour reinforced high density polyethylene composites

Abstract

Wood flour reinforced high density polyethylene (HDPE) composites have been prepared and their rheological properties measured. The melt viscosity decreased as the processing temperature increased and the wood flour content decreased. A power law model was used to describe the pseudoplasticity of these melts. Adding wood flour to HDPE produced an increase in tensile strength and modulus. Composites compounded in a twin screw extruder and treated with a coupling agent (vinyltrimethoxysilane) or a compatibliser (HDPE grafted with maleic anhydride) exhibited better mechanical properties than the corresponding unmodified composites because of improved dispersion and good adhesion between the wood fibre and the polyalkene matrix. Scanning electron microscopy of the fracture surfaces of these composites showed that both the coupling agent and compatibiliser gave superior interfacial strength between the wood fibre and the polyalkene matrix.     

Structure development and property changes in high‐density polyethylene/calcium carbonate blends during pan‐milling

A new self‐designed mechanochemical reactor, inlaid pan‐mill, was used in studying high density polyethylene (HDPE) and calcium carbonate (CaCO₃) blends. The effects of CaCO₃ on the crushing and structure of HDPE matrix and the properties of HDPE/CaCO₃ blends were investigated. Scanning electron microscopy, Fourier transformed IR spectroscopy, dynamical mechanical testing analysis, capillary rheometer, and Instron material testing system were used to characterize the structure of HDPE and evaluate the properties of HDPE/CaCO₃ blends. The introduction of calcium carbonate during milling improved milling efficiency, and time needed for each cycle was greatly reduced. Oxygen‐containing groups on HDPE chains, which were produced during milling, increased interfacial interactions and improved the dispersion and distribution of calcium carbonate particles in HDPE/CaCO₃ blends. Rheological, thermal, and mechanical properties were also improved. The elongation at break of milled blends with high concentrations of calcium carbonate was significantly higher than that of unmilled blends. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1459–1464, 1999     

Analysis of mechanical,thermal, and morphological behavior of polycaprolactone/wood flour blends

In the present study, the properties of polycaprolactone (PCL) and wood flour (WF) blends were examined by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), Instron mechanical tester, and scanning electron microscopy (SEM). As for results, the mechanical properties of PCL were lowered obviously, due to the poor compatibility between the two phases, when it was blended with wood flours. A fine dispersion and homogeneity of wood flour in the polymer matrix could be obtained when the acrylic acid grafted PCL (PCL‐g‐AA) was used to replace PCL for manufacture of blends. This better dispersion is due to the formation of branched and crosslinked macromolecules since the PCL‐g‐AA copolymer had carboxyl groups to react with the hydroxyls. This is reflected in the mechanical and thermal properties of the blends. In comparison with pure PCL/WF blend, the increase in tensile strength at break was remarkable for PCL‐g‐AA/WF blend. The PCL‐g‐AA/WF blends are more easily processed than the PCL/WF ones since the former had lower melt viscosity than the latter. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1000–1006, 2004     

HDPE/expanded graphite nanocomposites prepared via masterbatch process

High Density Polyethylene (HDPE) was melt extruded with different amounts of expanded graphite (EG) based masterbatches. Conductive composites were obtained by diluting PE and PS masterbatches with 60 wt% content of expanded graphite. These masterbatches were readily dispersed into the molten HDPE matrix yielding well‐dispersed HDPE/EG nanocomposites which couldn't be done by direct melt extrusion process under the same conditions. Electrical conductivity measurements showed a reduced percolation threshold by this masterbatch filling technique while the resulting composites were 2–3 orders of magnitude lower than that of direct melt extrusion because EG sheets were effectively encapsulated by PE or PS carriers in these masterbatches which leads to a better EG dispersion in composites. Both scanning electron microscopy (SEM) and X‐Ray diffraction (XRD) proved an excellent dispersion of EG in polymer matrix with the worm‐like structure tended to break into pieces under intensive rolling. The improvements in mechanical and thermal properties have been studied for the nanocomposites as prepared by masterbatch process. The results depended greatly on the dispersion of EG and the compatibility between masterbatch and HDPE matrix. POLYM. ENG. SCI., 47:882–888, 2007. © 2007 Society of Plastics Engineers     

The effect of expanded graphite on the physical properties of conductive EVA/wax phase change blends for thermal energy storage

A study of the morphology, dynamic mechanical, impact, and tensile properties of ethylene vinyl acetate copolymer (EVA)/expanded graphite (EG) and EVA/wax/EG composites is presented. The composites were prepared by melt blending. The EVA/EG composites showed ductile behavior, while brittle behavior was observed in the presence of wax. A finer dispersion of EG was observed in the matrix when wax was present. The storage modulus of the EVA/wax/EG composite was higher than that of the EVA/EG composite, which is ascribed to a better interaction between the EVA and the wax‐covered EG that significantly reduced the EVA chain mobility. The composites showed a decrease in impact strength with increasing EG and wax contents. There was a significant difference in the elongation at break between the EVA/EG and EVA/wax/EG composites, and little change in Young's modulus of EVA in the presence of EG and with increasing EG content. However, Young's modulus of the EVA/wax blends increased in the presence of and with increasing EG content. In all the investigated samples containing EVA and wax, irrespective of the EG content, the stress at break decreased with an increase in wax content. POLYM. COMPOS., 37:3025–3032, 2016. © 2015 Society of Plastics Engineers     

Comparative study of maleated polypropylene as a coupling agent for recycled low‐density polyethylene/wood flour composites

The effects of the type of coupling agent and virgin polypropylene (PP) content on the mechanical properties and water absorption behavior of recycled low‐density polyethylene/wood flour (WF) composites were investigated. The fractured surfaces of these recycled wood/plastic composites (rWPCs) were examined to gain insight into the distribution and dispersion of WF within the polymer matrix. The results indicate that the use of 100% recycled polymer led to inferior mechanical properties and to a greater degree of moisture absorption and swelling when compared to recycled polymer–virgin PP wood/plastic composites. This could have been related to the poor melt strength and inferior processability of the recycled polymer. The extent of improvement of the mechanical properties depended not only on the virgin PP content in the matrix but also on the presence of maleic anhydride (MA) modified PP as the coupling agent. Higher concentrations of MA group were beneficial; this improvement was attributed to increased chemical bonding (ester linkages) between hydroxyl moieties in WF and anhydride moieties in the coupling agent. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dynamic mechanical properties,crystallization behaviors,and low‐temperature performance of polypropylene random copolymer composites

In this study, polypropylene random copolymer (PPR) composites were prepared by the addition of either three kinds of thermoplastic rubber (TPR) modifiers (types 2088A, 2095, and 2096) or an ethylene–octene copolymer (POE)/high‐density polyethylene (HDPE; 2 :1 w/w) blend. Differential scanning calorimetry, wide‐angle X‐ray diffraction, and dynamic mechanical analysis were used to characterize the crystallization behaviors and dynamic mechanical properties of the PPR composites. The results indicated that PPR/POE/HDPE and PPR/TPR2088A had better comprehensive mechanical properties, especially the low‐temperature toughness among all of the samples. The obtained PPR/POE/HDPE blends showed a high toughness and good stiffness in the temperature interval from ?10 to 23°C with the addition of only 10 wt % POE/HDPE. When the temperature continued to fall below ?10°C, the PPR/TPR2088A composites exhibited a better impact toughness without a loss of too much stiffness. The good low‐temperature toughness of those two composites was attributed to both the decrease in the crystallinity and the uniform dispersion, obvious interfacial adhesion, and cavitation ability of POE/HDPE and TPR2088A in the PPR matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42960.     

Interfacial modification of high density polyethylene/glass fiber reinforced and non reinforced polyamide 66 blends

High density polyethylene (HDPE) and polyamide (PA66) are well known to be incompatible. An ionomer (Surlyn) was added as a compatibilizer to HDPE and glass fiber reinforced (HDPE/GFRPA66) and non‐reinforced (HDPE/PA66) blends. Two compositions were considered: 25/75 wt % and 75/25 wt %, with an emphasis on the former formulation. The influence of the compatibilizer on the rheology, thermal properties, and the morphology, as well as mechanical properties of the blends, was investigated using melt flow index measurements, DSC, scanning electron microscopy (SEM), and impact strength. The ionomer was found to be more effective as a compatibilizer with HDPE as a minor phase compared to the case when HDPE becomes the major phase. The results indicated that the interfacial properties of the blends were improved, with a maximum appearing at a critical concentration of the ionomer (7.5 vol %). At this level of compatibilization, SEM analysis revealed better interfacial adhesion and a finer dispersion. MFI results revealed a probable reaction between the amine groups of PA66 and the acid functions of the ionomer. The mechanical properties support the above results and showed that the addition of 25 wt % HDPE did not affect the properties of PA66 much and the presence of glass fiber did not hinder the effect of the compatibilizer. Only 20% decrease in notched Izod impact strength of the blends is observed at 7.5 vol % ionomer content, suggesting that the addition of 25 wt % of HDPE to PA66 is not detrimental at this level of compatibilization. The emulsification curve was established and revealed that, in terms of impact properties, the finer the particle size, the higher the impact strength corresponding to 7.5 vol % ionomer content. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1748–1760, 2005     

Microstructure and mechanical behavior of polyamide 66‐precipitated calcium carbonate composites: Influence of the particle surface treatment

The effects of interfacial adhesion strength on the mechanical behavior of composites of polyamide 66 and precipitated calcium carbonate (CaCO₃) particles have been investigated. The 50 nm average diameter particles have been surface‐treated using two kinds of coupling agent having various affinities with respect to the matrix. The surface‐modified particles have been incorporated into the polyamide matrix via melt processing. Tensile and impact tests, associated with dynamical mechanical analysis, have been performed on injection‐molded samples. The structural characterization of the specimens has been carried out using differential scanning calorimetry and wide‐angle X‐ray scattering. It is observed that the matrix structure is roughly insensitive to the surface treatment, despite a weak nucleating effect of the filler particles. In contrast, the particle surface treatment strongly influences the particle dispersion in the polymer matrix. Although dispersion was not optimized, the elastic properties of the reinforced polyamide increase with the CaCO₃ content, below as well as above the glass transition temperature. Impact toughness decreases for CaCO₃ weight fraction greater than 5%. Scanning electron microscopy investigation reveals that the interfacial adhesion affects local deformation processes, such as debonding and fibrillation of the polymer matrix around the particles, during the macroscopic deformation of the composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 989–999, 2006     

Morphological,mechanical, and physical properties of composites made with wood flour‐reinforced polypropylene/recycled poly(ethylene terephthalate) blends

Wood flour (WF)‐filled composites based on a polypropylene (PP)/recycled polyethylene terephthalate (r‐PET) matrix were prepared using two‐step extrusion. Maleic anhydride grafted polypropylene (MAPP) was added to improve the compatibility between polymer matrices and WF. The effects of filler and MAPP compatibilization on the water absorption, mechanical properties, and morphological features of PP/r‐PET/WF composites were investigated. The addition of MAPP significantly improved mechanical properties such as tensile strength, flexural strength, tensile modulus, and flexural modulus compared with uncompatibilized composites, but decreased elongation at break. Scanning electron microscopic images of fracture surface specimens revealed better interfacial interaction between WF and polymer matrix for MAPP‐compatibilized PP/r‐PET/WF composites. MAPP‐compatibilized PP/r‐PET/WF composites also showed reduced water absorption due to improved interfacial bonding, which limited the amount of absorbable water molecules. These results indicated that MAPP acts as an effective compatibilizer in PP/r‐PET/WF composites. POLYM. COMPOS., 38:1749–1755, 2017. © 2015 Society of Plastics Engineers     

Creep resistance of wood‐filled polystyrene/high‐density polyethylene blends

Creep, the deformation over time of a material under stress, is one characteristic of wood‐filled polymer composites that has resulted in poor performance in certain applications. This project was undertaken to investigate the advantages of blending a plastic of lower‐creep polystyrene (PS) with high‐density polyethylene (HDPE) at ratios of 100:0, 75:25, 50:50, 25:75, and 0:100. These various PS–HDPE blends were then melt blended with a short fiber‐length wood flour (WF). Extruded bars of each blend were examined to measure modulus of elasticity and ultimate stress. Increasing the ratio of WF increased modulus of elasticity in all composites, except between 30 and 40% WF, whereas the effect of WF on ultimate stress was variable, depending on the composite. Scanning electron microscopic images and thermal analysis indicated that the wood particles interacted with the PS phase, although the interactions were weak. Finally, creep speed was calculated by using a three‐point bending geometry with a load of 50% of the ultimate stress. Creep decreased only slightly with increasing WF content but more significantly with increasing PS content, except at pure PS. The WF/75PS–25HDPE blend showed the least creep. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 418–425, 2001