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The inflammability of wood fiber/high‐density polyethylene composites (WPCs/HDPE) remains a limitation for its application. Here the authors sought to improve the flame retardancy of WPCs by incorporating uniformly dispersed SiO2. Specifically, micron‐ and nano‐SiO2 were incorporated into HDPE via dry blending (dry dispersion) or solution blending (wet dispersion), to prepare the compounded matrices for the WPCs. The effects of SiO2 size and dispersion mode on the thermal stability and fire retardancy of WPCs were investigated. The results indicated that the nano‐SiO2 was more beneficial to improve the thermal stability of WPCs than the micron‐SiO2, especially incorporating via wet dispersion. The cone calorimetry tests revealed that incorporating 9 wt% micron‐SiO2 slightly decreased the heat release and smoke production of the WPCs. The incorporation of nano‐SiO2 in WPCs showed a moderate reduction in the heat release, while slightly increased the smoke production. The wet dispersion presented minor advantage over dry dispersion in improving the flame retardancy of WPCs. In addition, the dynamic thermal‐mechanical analysis revealed that the WPCs containing wet‐dispersed micron‐ or nano‐SiO2 exhibited a higher storage modulus compared to that dry‐dispersed SiO2. [ABSTRACT FROM AUTHOR]

Highlights: [•] Removal of hemicellulose reduced water absorption and thickness swelling. [•] Removal of lignin caused the highest tensile modulus and storage modulus. [•] WPCs with αC had the highest tensile strength, elongation at break, and toughness. [Copyright &y& Elsevier]

Kevlar fiber [KF; poly( p-phenylene terephthalamide)] can be used as a reinforcing element to improve the mechanical properties of the resulting wood thermoplastic composites. This study was devised to investigate the effects of incorporation of KF on the isothermal crystallization kinetics of high-density polyethylene (HDPE) in the resulting composites using differential scanning calorimetry. Avrami model was applied to describe the isothermal crystallization process, and the fold surface-free energy was calculated according to the Hoffman-Lauritzen theory. Comparative study of neat HDPE, wood flour/HDPE composite (WPC), virgin KF-reinforced WPC (KFWPC), and grafted Kevlar fiber (GKF)-reinforced WPC (GKFWPC) showed that the overall crystallization rate, the activation energy, the equilibrium melting temperature, and the fold surface-free energy of the WPC were apparently changed due to the addition of KF; the crystallizability exhibited an order of KFWPC > GKFWPC > HDPE > WPC. The incorporation of virgin KF may cause the heterogeneous nucleation to induce a change in the crystal growth of HDPE from the tridimensional to bidimensional or to the mixed patterns. Avrami exponent values of the composites decreased with time, confirming the change of crystallization behavior. This study demonstrates that both the KF and GKF can act as nucleating agents to improve the crystallization rate of HDPE. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

The influence of nano-silica (nSiO2) and micro-silica (mSiO2) in the shell and wood fiber filler in the core on the thermal expansion behavior of co-extruded wood/polyethylene composites (Co-WPCs) was investigated to optimize the thermal expansion resistance. The cut Co-WPCs samples showed anisotropic thermal expansion, and the thermal expansion strain and linear coefficient of thermal expansion (LCTE) decreased by filling the shell layer with rigid silica, especially nSiO2. Finite element analysis indicated that the polymer-filled shell was mainly responsible for the thermal expansion. The entire Co-WPCs samples exhibited a lower thermal expansion strain than the cut Co-WPCs samples due to protection by the shell. Increasing the wood fiber content in the core significantly decreased the thermal expansion strain and LCTE of the Co-WPCs. The Co-WPCs whose core layer was filled with 70% wood fiber exhibited the greatest anisotropic thermal expansion. [ABSTRACT FROM AUTHOR]

• Coextruded wood plastic composites (Co-WPCs) were prepared with highly filled core layer. • The flexible shell layer acted as a stress transferring medium avoiding stress concentration for Co-WPCs. • The HDPE shell layer endowed the Co-WPCs with twice impact strength than controls. • Core/shell structure can markedly improve dimensional stability at high wood flour contents. To obtain an optimum balance in performance and cost, this study aims to investigate the effect of wood flour (WF) content in both shell and highly filled core layers on the mechanical properties, creep behavior, and dimensional stability of the resulting coextruded WF/high density polyethylene composites (Co-WPCs). Scanning electron microscopy showed good interfacial adhesion between the core and shell layers. The flexural strength and modulus of the Co-WPCs increased with increasing WF content in shell layer, while the flexural strain and impact strength decreased but still higher than those of the core-only controls. Finite element analysis showed that the coextruded flexible shell layer acted as a stress transferring medium avoiding stress concentration and endowed the Co-WPCs with higher toughness. Increasing the content of rigid WF in both the core and shell layers resulted in significant reduction in creep strain. Coating the highly filled core layer with less filled shell layer can markedly reduce the water absorption and thickness swelling. For Co-WPCs with 70 wt% WF in core layer and 20 wt% WF in shell layer, the flexural strength, modulus, and creep strain were comparable to those of the core-only control, but the flexural strain, impact strength, and water resistance were much better. [ABSTRACT FROM AUTHOR]

[Display omitted] • UH-WPCs were successfully fabricated using recycled PP and waste WF. • R-PP protected WF from damage due to the improved wettability and plasticization. • UH-WPCs exhibited more complex solid-like rheological behavior than the traditional WPCs. • This study formalizes a sustainable strategy for full-component utilization of the industrial waste and residue. The development of wood-plastic composites (WPCs) is one of the key scientific interests in recent years for recycling industrial waste and reducing environmental pollution risks. In this study, low-cost and high-strength ultra-high-filled wood fiber/polypropylene composites (UH-WPCs) were fabricated using recycled polypropylene (R-PP) as the polymer matrix and 60–85 wt% recycled wood fiber (R-WF) from the waste sawdust of phenolic resin enhanced wood products as reinforcement. The UH-WPCs possessed robust mechanical properties and better creep resistance than composites using original WF or PP due to the sufficient R-WF/R-PP interface interaction. Specifically, compared with R-WF/PP composites, the maximum increases in the tensile, flexural, and impact strength of the R-WF/R-PP composites at 80 wt% R-WF content were 94.30%, 89.66%, and 96.33%, respectively. The Burges model could well predict the solid-like rheological behavior of UH-WPCs. This study formalizes a preventive sustainable strategy for full-component utilization of the industrial waste and residue. [ABSTRACT FROM AUTHOR]

[Display omitted] • The maximum filler content of wood plastic composites (WPCs) is increased to 90 wt% by profile extrusion. • The PP matrix with moderate melt flow index (MFI) is beneficial to the preparation of ultra-highly filled WPCs with excellent comprehensive mechanical properties. • The PP matrix with low MFI is suitable for ultra-highly filled WPCs to obtain better dimensional stability and creep resistance. • This work provides an important reference for the high-performance ultra-highly filled WPCs. Simultaneous realization of high filler fraction and excellent comprehensive properties remains a great challenge for extruded wood plastic composites (WPCs). Herein, ultra-highly filled bamboo fiber/polypropylene composites (UH-BPCs) with total filler content varying from 75 wt% to 90 wt% were fabricated via profile extrusion. Six kinds of polypropylene (PP) with melt flow indices (MFIs) ranging from 0.165 to 24 g (10 min)−1 were selected as the matrix. The tensile, flexural, impact strengths and dimensional stability of the UH-BPCs decreased with increasing filler content. However, a relatively high filler content (no more than 85 wt%) could improve the modulus and creep resistance of UH-BPCs. At 85 wt% filler content, the UH-BPCs with PP of moderate MFI exhibited the best mechanical properties with a tensile strength, tensile modulus, flexural strength, flexural modulus, and unnotched impact strength of 22.39 MPa, 6.05 GPa, 39.86 MPa, 7.19 GPa, and 4.22 kJ m−2, respectively. The UH-BPCs with low MFI PP presented better dimensional stability and creep resistance, especially at high temperatures. This work can provide an important reference to prepare ultra-highly filled WPCs with high performance via profile extrusion. [ABSTRACT FROM AUTHOR]