In this research, wood flour (WF) was modified using sodium–montmorillonite (Na-MMT) at four different concentrations (0.5, 1.0, 2.0, and 4.0 wt%, respectively) and didecyl dimethyl ammonium chloride (DDAC) in a two-step process to form organo-montmorillonite (OMMT) inside the WF or attached to the WF surface. The thus-modified WF was then mixed with poly(lactic acid) (PLA) to produce WF/PLA composites. The thermal stability of these composites with respect to their resistance against both thermal deformation and thermal decomposition was characterized by stress relaxation, differential scanning calorimetry (DSC), and thermogravimetric (TG) analysis. Besides, the activation energies for thermal decomposition of the composites were calculated. The results showed the following: (1) The modification of WF by OMMT improved the resistance against thermal deformation of the composites at appropriate OMMT loadings (lower than 1 wt% in this study). However, after introducing excessive OMMT, the enhancements in thermal stability diminished. Composite containing WF modified by 0.5 wt% of OMMT showed the optimal thermal deformation stability in this study, reflected in the highest values of thermal properties such as the glass transition temperature, melting temperature, crystallization temperature, and slowest stress relaxation rate. (2) OMMT showed a negative effect on the resistance against thermal decomposition. Namely, OMMT accelerated the thermal decomposition of the composites, probably by the easier degradation of the organic surfactant used for the WF modification. However, this behavior might be favorable for achieving fire retardancy. POLYM. COMPOS., 37:1971–1977, 2016. © 2015 Society of Plastics Engineers

In this study, micronized organo-montmorillonite (OMMT) suspension was prepared with sodium-montmorillonite (Na-MMT), didecyl dimethyl ammonium chloride, and dispersant polyethylene glycol 1000 by a ball-milling process. Then, wood flours (WFs) were impregnated with prepared OMMT suspension at a concentration of 0.5, 1.0, 2.0, or 4.0%. WFs were characterized by X-ray diffraction and scanning electron microscopy. The hygroscopicity of WF was investigated by a vapor adsorption method. WFs were, respectively, blended with poly (lactic acid) (PLA) to produce WF/PLA composites. Thereafter, physical, mechanical, and thermal properties of the composites were tested. The results showed that a great amount of OMMT attached on the surface of WF, partly penetrating into the microstructure of WF. Owing to the hydrophobicity of OMMT, the vapor adsorption of OMMT-modified WF decreased. The composite which was produced by WF treated with 0.5% OMMT suspension, showing an increment in the physical, mechanical, and thermal properties. However, OMMT should not be overloaded. Otherwise, the accumulation of OMMT might cause poor interfacial adhesion between WF and PLA matrix. POLYM. COMPOS., 36:731–738, 2015. © 2014 Society of Plastics Engineers

The purpose of this research was to investigate the influence of vitamin E (Ve) with different loading levels (0.1, 0.2, 0.4, and 1.2 %wt) on the photodegradation of wood flour/polypropylene composites. Five groups of composites were exposed in a QUV-accelerated weathering tester for 960 h and then the surface color and the flexural properties were tested. Besides, the surface morphology and chemical changes of the composites during weathering were analyzed by scanning electron microscopy, attenuated total reflectance fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results revealed that (1) the addition of Ve had a positive effect on hindering the photooxidation process of the composites; (2) composites with higher Ve loading levels (0.4 and 1.2 %wt) showed better flexural properties, less color fading, cracks, and disclosure of wood fibers on surface after weathering; (3) Ve alleviated the chain scission of PP and the formation of carbonyl groups by reacting with free radicals that generated from photodegradation during weathering. Therefore, it could be an effective antiphotodegradation agent for the composites. POLYM. COMPOS., 35:2085–2093, 2014. © 2014 Society of Plastics Engineers

To quantitatively evaluate the effect of maleic anhydride grafted polypropylene (MAPP) as a coupling agent on interfacial compatibility between wood and polymer in wood/polypropylene (PP) composite, the dielectric constant and dielectric loss factor were measured for poplar (Populus tomentasa Carr.) wood flour/polypropylene (PP) composites prepared with six MAPP loading levels (0.5, 1.0, 1.5, 2.0, 4.0, and 8.0%), and the Cole–Cole plots, the dielectric relaxation strength, the distribution of relaxation time and the activation thermodynamic quantities of the dielectric relaxation based on the reorientation of the methylol groups (CH₂OH) in the amorphous region of wood cell wall were further analyzed. The results showed that the dielectric relaxation strength decreased with the MAPP loading and dropped to the lowest at MAPP loading of 2.0%, after which it kept almost constant. It suggested that the internal bonding between wood and PP molecules was the strongest at 2.0% MAPP, therefore the reorientation of the methylol groups in wood became very difficult under the strong hindrance from the long-chained PP molecules and the physical or/and chemical bonds between MAPP, wood flour, and PP in the composites. The activation free energy ΔE could be served as the indicator to quantitatively evaluate the effect of MAPP on interfacial compatibility of the wood/PP composites. ΔE of 2.0% MAPP modified composites showed the maximal value among all the tested conditions, which was 33.52 kJ mol⁻¹; while the values for 1.5 and 4.0% MAPP modified were 23.35 and 21.75 kJ mol⁻¹. Therefore, excessive MAPP was not beneficial to improve the internal compatibility of wood/PP composites, but had negative effect. POLYM. COMPOS., 35:489–494, 2014. © 2013 Society of Plastics Engineers

This study aimed to investigate the combination effect of glycerin treatment and thermal modification of wood flour on the physical, mechanical, thermal dynamic mechanical properties of wood flour/polypropylene (PP) composite. The morphological aspect was also investigated. The wood flour was first impregnated in the aqueous solution of glycerin, followed by heat treatment at 200°C for 1 h. Then the unmodified or modified wood flour was blended with PP at a weight ratio of 4:6 to prepare composites. Moisture adsorption experiment and X-ray photoelectron spectroscopy analysis of wood flour demonstrated that the hygroscopicity and the free surface hydroxyl groups of wood flour decreased after glycerin-thermal modification. Thickness swelling of the 10% wt glycerin-thermally modified wood flour/PP composite was reduced by 42.8% after 96 h immersion as compared to unmodified control. Evaluation of mechanical properties in impact and flexure modes indicated that glycerin treatment alone had no significant effect, but the combination of glycerin and thermal treatment slightly decreased the strength, with the exception of 10% glycerin and heat modified sample. Dynamic mechanical analysis and scanning electron microscope illustrated the improved interfacial bonding between PP and wood flour modified by 10% glycerin and heat treatment. POLYM. COMPOS., 35:201–207, 2014. © 2013 Society of Plastics Engineers

To investigate the effects of two types of clay, namely, Na-montmorillonite (Na-MMT) and organic-montmorillonite (OMMT), on poly(lactic acid) (PLA)/wood flour (WF) composites, some physical and mechanical properties including the water sorption, thickness swelling, flexural modulus of rupture (MOR), and modulus of elasticity (MOE) of PLA/WF composites at different WF contents of 0, 20, 40, and 60 wt% were tested in this study. The results showed that: (1) the 24 h water uptake and thickness swelling increased and the flexural MOR and crystallinity decreased with the increasing WF content, whereas the flexural MOE of the composites increased with WF content up to 40 wt% but decreased sharply at WF content of 60 wt%; (2) the addition of Na-MMT slightly increased the 24 h water uptake as well as the thickness swelling rate below 40 wt%, whereas OMMT reduced the thickness swelling at higher WF contents (40, 60 wt%) although it showed little effect on 24 h water uptake; (3) both Na-MMT and OMMT could improve the flexural MOR and MOE of PLA/WF composite at WF contents below 40 wt%, and OMMT resulted in more obvious improvement than Na-MMT. However, they both showed negative effect at WF content of 60 wt%; (4) XRD and FT-Raman analysis suggested that clays would be attached more on the surface of the WF rather than diffused in the PLA matrix at a higher WF content (60 wt%); (5) SEM analysis proved that the interfacial adhesion of PLA and WF became poorer at WF content above 40 wt%, whereas it could be improved by OMMT modified. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

To clarify the interaction between the wood and polymer in wood flour/polymer composites, the dielectric constant and dielectric loss factor values were measured for poplar (Populus tomentasa Carr.) wood flour/polypropylene (PP) composites with different wood contents. The dielectric relaxation strength, distribution of relaxation time, and activation thermodynamic quantities of the dielectric relaxation caused by the reorientation of the methylol groups (CH₂OH) in the amorphous region of the wood cell wall were then calculated. The results show that the dielectric relaxation strength changed very little below a wood content of 40% and began to increase above that value; this was due to the strong hindrance of PP to the reorientation of methylol groups and, therefore, suggests a close interaction between the wood and PP below a wood content of 40%. The low distribution coefficient of the relaxation time at extremely low temperatures below a 40% wood content was also found; this indicated that some groups in the wood could not move because of the influence of PP. The apparent activation energy increased with wood contents below 40% and then decreased; this further confirmed the optimal interfacial compatibility at a 40% wood content in the wood flour/PP composites in the absence of additives. This result was consistent with the results we obtained by a stress-relaxation approach. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

To investigate the interfacial compatibility of wood flour/polypropylene (PP) composite, compressive stress relaxation curves at different temperatures (26, 40, and 60°C) were determined at various wood contents (0, 20, 30, 40, 50, 60, and 70%) without coupling agent and further determined at wood contents of 50 and 60% by using maleic anhydride grafted polypropylene (MAPP) and silane as coupling agents. The apparent activation energy (▵E) was also calculated according to the Eyring's absolute rate reaction theory. The results showed that the stress relaxed faster at higher temperatures. ▵E of wood flour/polypropylene composites without coupling agent showed the highest value at wood content of 40%, suggesting that the best interfacial compatibility between wood and PP occurred at 40% wood content. Adding coupling agents increased ▵E obviously at higher wood contents (50 and 60%). With the increasing loading level of coupling agents, ▵E increased at first and then decreased gradually or finally reached a constant level depending on the type of coupling agent. The optimal loading of coupling agent corresponding to the highest ▵E value was related to wood content and the type of coupling agent. Within the experimental conditions used in this study, the optimal loading level for MAPP was 2% at both wood contents while for silane it was 1.5% and 2% at wood content of 50 and 60%, respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012