Morphology, dimensional stability and mechanical properties of polypropylene–wood flour composites with and without nanoclay

Influence of wood flour and modifier contents on the physical and mechanical properties of wood flour-recycle polypropylene composites

The mechanical properties of composites from recycled waste plastic and waste sawdust are of interest in trying to convert these waste streams to useful products. The development of these composites from natural fiber is therefore receiving widespread attention due to the growing environmental awareness. The effects of compositions were investigated including different grades of plastic (virgin and recycled) and amounts of wood flour, coupling agent, and ultraviolet (UV) stabilizer on mechanical and physical properties of polypropylene/rubberwood flour (RWF) composites. Virgin polypropylene gave better mechanical properties than recycled (recycled polypropylene (rPP)), both in composites and as unfilled plastic. RWF content exceeding 25 wt% enhanced the strength of RWF-reinforced rPP composites. The modulus and hardness of composites increased linearly with wood flour loadings. Maleic anhydride-grafted polypropylene (MAPP) as a coupling agent increased the strength, modulus, and hardness of the composites. However, addition of 1 wt% UV stabilizer degraded the mechanical properties. Therefore, 4 wt% MAPP content is recommended to achieve good mechanical properties of rPP/RWF composites, while the amount of UV stabilizer should be as small as possible to avoid its negative influence.

In this research, the improvement of the impact strength of wood flour–recycled polypropylene (PP) composites through impact modification was studied. For this purpose, a virgin polypropylene (VPP) was thermomechanically degraded by five extrusions under controlled conditions in a twin‐screw extruder at a rotor speed of 100 rpm and a temperature of 190°C. PP (VPP and recycled PP at the second and fifth stages) and wood flour were compounded at 50 wt % wood flour loading in a counterrotating twin‐screw extruder in the presence different contents of ethylene vinyl acetate (EVA) to produce the wood flour–PP composites. From the results, the composites containing recycled PP exhibited significantly lower impact strengths. The addition of EVA up to 9 wt % increased the impact strengths of the composites made with PP recycled two and five times by about 63 and 41%, respectively. The composites containing VPP exhibited higher impact strengths than those containing recycled PP and EVA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

In recent years, the natural fibers as reinforcement have been increasingly used to replace the conventional inorganic filler in polymer matrix composites. Especially, natural filler reinforced thermoplastics have a good potential in the future as a substitution for wood-based material in many applications. Natural fibers render several advantages, i.e. the filler cost is usually very low. Also, the natural fillers are biodegradable (thus contributing to an improved environmental impact). In addition, this kind of filler is naturally renewable as well. Moreover, many mechanical and thermal properties can be enhanced. In this work, Hevea Brasiliensis woodflour filled polypropylene composites were prepared by twin screw extruder followed by injection molding. In the first part of this study, the aims are to determine the effect of polypropylene types (PP-HP644T, PP-HP648N and PP-HP740H), average particle sizes, filler contents and sized distributions on the mechanical, thermal and some related physical properties. The experimental results revealed that the composites based on high melt flow rate polymer matrix (PP-HP644T) had higher mechanical properties than those of wood flour composites with PP-HP648N and PP-HP740H. For the effect of particle sizes, filler contents and sizes distributions, it was found that the particle sizes and woodflour contents played a significant role in the mechanical properties of wood flour composites. Flexural and tensile modulus increased, while flexural and tensile strength decreased with increasing woodflour contents. Furthermore, the average particle size of woodflour that was suitable for improving the mechanical properties of the composite was about 200-300 µm. The appropriate bimodal particle sizes that rendered the greatest packing density of wood flour were 275 µm and 49 µm at a mass ratio of 73:27. Additionally, it was found that the thermal stability and degradation temperature (at 5% weight loss) of wood flour composites decreased with increasing woodflour mass fraction. In the second part, maleic anhydride grafted polypropylene (MAPP) was used as a coupling agent to improve the interfacial bond strength between woodflour filler and polymer matrix. The influence of the amount of MAPP on mechanical and thermal properties of woodflour composites has been investigated. This work recommends MAPP content of 5 wt% (of woodflour) to be introduced into the woodflour composites for optimization of the composite mechanical properties. It was reported that the flexural and tensile strength were 110% and 87% higher than those of the woodflour composite without MAPP, respectively. The thermal stability and degradation temperature of woodflour composites containing the coupling agent were slightly increased with increasing coupling agent content.

Virgin polypropylene (PP), recycled polypropylene (RPP) and acrylonitrile butadiene rubber (NBR) were mixed together to prepare ternary blends (PP/RPP/NBR) of thermoplastic vulcanisates (TPVs). The blends comprised 30 parts per hundred (phr) NBR and 70 phr PP and RPP. Sulphur was used to dynamically crosslink the NBR during the blending process. Maleic anhydride grafted polypropylene (MA-g-PP) was used as compatibiliser to enhance the interaction of the polypropylene and the rubber. In this study, the loading of RPP in the TPVs was varied and the effects on mechanical and rheological properties were studied. The hardness and the tensile strength of the TPVs increased upon increasing the RPP loading. The RPP exhibited an adverse effect on elongation-at-break of the vulcanisates, with the pseudo-plastic flow behaviour and the viscosity of the vulcanisates increasing with the increased loading of RPP.

Recycled polypropylene was reinforced with treated and non-treated wood flour with different natural oils. Four natural oils were used as coupling agents, namely hexanoic (C6), octanoic (C8), decanoic (C10) and dodecanoic (C12) acids. The mechanical, thermal and morphological properties of the resulting composites were evaluated. The usage of natural oils as coupling agents clearly improved the interfacial adhesion between wood flour and the polypropylene matrix while enhancing the mechanical and thermal properties. Better results were obtained when C8 was used. The improvement in the mechanical and thermal properties of the composites imparted by C8 is similar to that promoted by maleic anhydride-grafted polypropylene. The mechanical and thermal properties of the composites were affected by the boiling temperature and chain length of the natural oil used.

In this research, polypropylene composites filled with Hevea Brasilliensis wood flour at filler content up to 60 wt% were prepared and investigated in order to determine the effects of polymer melt flow rate (MFR), number of reprocessing times, filler size, and filler content on thermal and mechanical properties. The results reveal that the composites of polypropylene with higher melt flow rate (lower viscosity) provided greater values of flexural and tensile properties. The study additionally exhibits the recyclability potential without losing mechanical properties. Furthermore, both flexural and tensile modulus increased, while both flexural and tensile strength decreased with increasing wood flour contents. In addition, the average particle size of wood flour that was suitable for improving the mechanical properties was approximately 200-300 μm. In the last section of the research, the effects of maleic anhydride grafted polypropylene (MAPP) coupling agent were investigated. It is worth noting that, the flexural strength and tensile strength of highly filled composites with MAPP at 5 wt% (based on wood flour) were approximately 110% and 87% higher than those of the composites without MAPP, respectively. In the presence of coupling agent, the enhancement of interfacial adhesion was analyzed using scanning electron microscope (SEM).

Wood plastic composites (WPC) have been produced by compounding meranti wood flour (WF) with polypropylene (PP) copolymer using a twin-screw extruder. The meranti WF content was varied from 30 to 60 wt.%. The mechanical properties, i.e. tensile, flexural and impact of the composites were determined on injection-molded specimens. The tensile fractured surfaces were used to study the morphological properties of the composites. The result shows that the increment in WF content has given a significant improvement in modulus properties but at the expense of strength and toughness properties. A commercial maleic anhydride grafted polypropylene (MAPP) compatibilizer at 5 wt.% was incorporated into the PP40/WF60 formulation. The strength, stiffness and toughness properties were improved significantly in the presence of MAPP. The morphology of the composites was studied by scanning electron microscopy (SEM). The improvement of the fibre-matrix adhesion between the WF and PP matrix as revealed by SEM is believed to be one of the major reasons for the improved mechanical properties.

This paper aims to investigate the water absorption of wood flour/polypropylene composites and its effects on dimensional stability and crystallization properties. Wood-plastic composites (WPCs) makes using polydopamine modified wood flour (WF-D), virgin polypropylene, maleic anhydride-grafted polypropylene (MA) and antioxidant, by using hot-pressing moulding. Water absorption (WA), thickness swelling (TS) and failure of flexural properties of the composites have studied for a range of immersion times. It is found that the WA and TS have increased with WF content and immersion time. The water absorption and thickness swelling of WPCs are 0.85% and 0.99%, respectively, after 8 days immersion. With the prolonging of immersion time, the impact strength, flexural strength and flexural modulus of WPCs increase first and then decrease. The impact strength decreases from 3.32 kJ/m2 to 2.94 kJ/m2, the retention rate is 88.55%; the flexural strength and flexural modulus by 68.58 Mpa and 3.92 Gpa, respectively. WPCs crystallization and thermal properties decrease slightly. Microstructures of the composites are examined to understand the mechanisms for the wood-plastic interaction which affects the water absorption and thickness swelling. Our work demonstrates that using polydopamine treatment wood flour for preparing WPCs can be an efficient way to improve the water resistance of WPCs.

Optimized material composition to improve the physical and mechanical properties of extruded wood–plastic composites (WPCs)

This study melt-blends polypropylene (PP), wood flour (WF), and far-infrared masterbatches into PP/WF wood plastic composites with far-infrared emissivity. During the process, maleic anhydride-grafted polypropylene (PP-g-MA) is added as the coupling agent between PP and WF. Mechanical property tests, scanning electron microscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), polarized light microscopy (PLM), and far-infrared emissivity are undertaken to evaluate various properties of the PP/WF wood plastic composites. The test results show that regardless of the WF content, mechanical properties of the composites remain at certain levels. The combination of 3 wt% PP-g-MA increases the interfacial adhesion between WF and PP, which in turn effectively increases the tensile strength by 20% and increases the flexural strength by 35%. The PP/WF wood plastic composites containing 4 phr (parts per hundreds of resin) of far-infrared masterbatches is 0.86 ɛ, which reaches the standard of good health care. The test results of XRD, DSC, and PLM show that the combination of both WF and far-infrared masterbatches helps the heterogeneous nucleating in PP, and increases the crystallization temperature of PP, but does not influence the crystalline structure of PP.

The physical and mechanical properties of wood-polymer composites made with virgin or recycled polypropylene, or a mixture of these were studied. The composites made with recycled polypropylene had higher density, lower porosity, and higher dimensional stability compared to the composites made with virgin polypropylene. Although the composites made with recycled polypropylene exhibited lower tensile strength than those made with virgin polypropylene, they had higher Charpy impact strength. Scanning electron microscopy analysis of the fractured surfaces of the composites showed no significant differences in the fracture mechanisms of the studied composites. The degree of crystallinity was estimated to be higher for the virgin polypropylene than for the recycled one.

Recycled polypropylene (RPP) and lignin represent by-products produced in enormous amounts worldwide that remain underutilized. This study used rice straw lignin as a filler at various concentrations (0% to 70% w/w) in RPP and virgin polypropylene (PP) composites by melt blending. Structural and morphological alterations of lignin were analyzed by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), respectively. Mechanical properties were evaluated using a universal testing machine (UTM). Results revealed that the tensile strength of the composites decreased as the lignin content increased, presumably due to the low of compatibility degree of lignin and MAPP, as well as the crack formation due to the agglomeration of lignin. However, composites with lignin as a filler showed higher moduli and water absorption capacities, as well as thickness swelling; using lignin as a filler caused a drastic reduction of the elongation at break values. The results indicated that the physical and mechanical properties of RPP and its virgin PP composites had no substantial differences. This indicated that virgin PP could be substituted by recycled polypropylene (RPP) for composite applications with the addition of MAPP.

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

In this study, the effect of natural weathering on the physical and mechanical properties of wood plastic composites (WPC) made from virgin and recycled polypropylene (PP) was studied. To prepare the recycled PP, virgin PP was thermo-mechanically degraded by extrusion under controlled conditions in a single-screw extruder at a router speed of 60 rpm and temperature of 190 °C. PP (virgin and recycled), wood flour, compatibilizer, and UV absorbent were physically blended, and the samples were manufactured by a twin-screw extruder. The samples were exposed to natural weathering for 270 days. The surface characteristics of the samples were investigated before and after weathering. According to the results, the composites from recycled PP exhibited a higher weathering resistancethan those from virgin PP. The use of a UV absorber improved the flexural strength and modulus of the composites, but it could not significantly prevent the flexural properties loss and discoloration of the composites after weathering.