Investigation of bulk and in situ mechanical properties of coupling agents treated wood plastic composites

This paper presents the interfacial optimisation and characterisation of WPC by the use of maleated and silane coupling agents (MAPE, Si69 and VTMS), and its effect on the bulk and in situ mechanical properties. The results showed the treated WPC possessed better interface by showing improved compatibility between the constituents, wettability of wood flour, and resin penetration in the SEM images. The enhanced interface led to the increase in the tensile strength and stiffness of the treated WPC, which was confirmed by their superior load bearing capacity, namely the higher storage moduli measured by DMA. The observed shift of the relaxation peak of the treated WPC indicated the constraints on the segmental mobility of the polymeric molecules resulted from the treatments. Nanoindentation investigation revealed that the in situ mechanical properties were subject to a number of phenomena including fibre weakening or softening impact, crystalline structure transformation and cell wall deformation, concluding that the bulk mechanical properties of WPC might not be governed by the local property of materials within the interface.     

Influences of extractives on the photodegradation of wood

Wood is susceptible to photodegradation when exposed to light. In addition to three main components of wood, the influence of extractives on photodegradation is not fully understood. This study examines the role of wood extractives in photodegradation process, and so the variations in the surface properties of non-extracted and extracted Cryptomeria japonica and Acacia confusa heartwood were examined after exposure to ultraviolet light. FTIR and UV-visible techniques were used to analyze the variations in chemical characteristics on the wood surfaces after irradiation. Following the lightfastness test, the contents of quinonoids and carbonyl groups derived from the lignin increased. However, the wood surface deteriorated less when the extractives existed. In conclusion, extractives play an essential role in the photodegradation of wood, and the rate of wood degradation was lessened by the presence of extractives.     

Influence of photostabilizers on wood flour-HDPE composites exposed to xenon-arc radiation with and without water spray

The weathering of wood-plastic composites changes their appearance and/or mechanical properties. These changes can be slowed through the addition of ultraviolet absorbers and pigments. The first phase of this study examined the effect of incorporating different concentrations of an ultraviolet absorber and/or pigment into wood-flour-filled high-density polyethylene (WF/HDPE) composites. Lightness and flexural properties of the composites were determined periodically during exposure to UV radiation and water spray in a xenon-arc type weathering apparatus. The influence of exposure type (UV radiation, with or without water spray) on the properties of photostabilized WF/HDPE composites was determined in the second phase of the study. The results showed that both ultraviolet absorbers and pigments provide protection against weathering of wood-plastic composites. The amount of protection can be influenced by both photostabilzer concentration and exposure variables.     

Effect of thermal-treatment of wood fibres on properties of flat-pressed wood plastic composites

This study aimed to enhance the dimensional stability of flat-pressed wood plastic composites (WPCs) containing fast growing wood fibres by a thermal-treatment method. The wood fibres were treated at three different temperatures (120, 150, or 180 °C) for 20 or 40 min in a laboratory autoclave. The WPC panels were made from dry-blended Eucalyptus camaldulensis wood fibres and polypropylene (PP) powder (50:50 by weight) using a conventional flat-press process under laboratory conditions. Thickness swelling and water absorption of the WPC panels significantly decreased with increasing the treatment temperature and time. The thermal-treatment of eucalyptus wood fibres slightly decreased the screw withdrawal resistance of the WPC panels as compared to the reference panels while the flexural properties and internal bond strength were more seriously affected by the treatment. The present study revealed that the thermal-treatment of the wood fibres significantly improved the dimensional stability of the WPC panels.     

Accelerated weathering of unbleached and bleached Kraft wood fibre reinforced polypropylene composites

In this paper, combined moisture/ultraviolet (UV) weathering performance of unbleached and bleached Kraft wood fibre reinforced polypropylene (PP) composites was studied. Composites containing 40 wt% fibre with 3 wt% of a maleated polypropylene (MAPP) coupling agent were fabricated using extrusion followed by injection moulding. Composite mechanical properties were evaluated, before and after accelerated weathering for 1000 h, by tensile and impact testing. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were also carried out to assess the changes occurring during accelerated weathering. Bleached fibre composites initially showed higher tensile and impact strengths, as well as higher thermal stability and greater crystallinity. During accelerated weathering, both unbleached and bleached fibre composites reduced tensile strength (TS) and Young's modulus (YM), with the extent of the reduction found to be similar for both unbleached and bleached fibre composites. Evidence supported that the reduction of TS and YM was due to PP chain scission, degradation of lignin and reduced fibre-matrix interfacial bonding.     

The effects of HALS in the prevention of photo-degradation of acrylic clear topcoats and wooden surfaces

A study of the photocatalytic degradation of an acrylic dispersion based coating and its prevention using hindered amine light stabilizers (HALS) was carried out on solid films by exposing them to Xenon arc light. The degradation rates were compared using FTIR-ATR techniques by plotting the differential build up of the hydroxyl and hydroperoxide bands as function of exposure time. UV-Vis spectroscopic studies were carried out as well to obtain data about the light stabilization of organic UV Absorbers (UVA) and inorganic UV screeners by HALS. The effectiveness of an aqueous primer comprising a specific lignin stabilizing HALS in combination with clear topcoats with UVA or UV screeners in the prevention of photo-induced discolouration of wooden surfaces was investigated by measuring the colour change during exposure time. It was shown, that the usage of HALS was effective in reducing the degradation speed of clear coats with UVA and UV screeners. Results obtained by UV-Vis spectroscopic analysis during the exposure cycle showed an inhibition of the photo-degradation of the UVA themselves, while no positive effect occurred on inorganic UV screeners. A lignin stabilizer containing aqueous primer with a specific HALS as active component, showed some promising results in combination with transparent topcoats comprising organic UVA and inorganic UV screeners, except ZnO, where a strong antagonistic effect occurred.     

动态力学分析方法在塑木复合材料研究中的应用

阐述了动态力学分析(DMA)方法在塑木复合材料研究中的应用现状,重点介绍了国内外运用动态力学方法分析塑木复合材料界面相容性的问题。使用各类改性剂改善塑木复合材料的界面相容性后,塑木复合材料的刚性增加,其储能模量比相容性差的复合材料要高。当用DMA的损耗角正切(tanδ)来分析塑木复合材料的界面相容性时,我们可以得出如下结论:对于填料纤维和塑料之间具有良好界面相容性的复合材料,由于强的界面粘结作用可以限制填料-基体界面链段的运动,往往使得tanδ的振幅值降低,而其对应的温度,即玻璃化转变温度(Tg)将移动到更高的温度,并且复合材料界面增强指数和弛豫过程的活化能越大,界面粘结强度越大。     

Stabilizing effect of extractives on the photo-oxidation of Acacia confusa wood

This study shows the photo-stabilizing effect of extractives on wood. XPS and FTIR techniques were used to analyze the variations in chemical characteristics on the surfaces of non-extracted and extracted Acacia confusa heartwood after lightfastness test. XPS survey analyses reveal that non-extracted heartwood exhibits a higher O/C ratio than the extracted wood. Furthermore, results from the detailed analysis of C1s indicated that the photo-oxidative derivatives increased in both extracted and non-extracted specimens after lightfastness test. On extracted wood, the derivatives are mainly derived from lignin, whereas extractives are the major component responsible for the generation of derivatives on non-extracted wood surface. After leaching test of UV-irradiated specimens, it was noted that the degradation products were readily removed by water. More water-soluble derivatives were leached out from the extracted wood, although higher lignin content was observed on the non-extracted wood surface. In conclusion, it is shown that photodegradation of A. confusa wood can be retarded by extractives oxidation.     

Effect of the nanosilica content in the shell of coextruded wood‐plastic composites to enhance the ultraviolet aging resistance

Weathering durability of wood‐plastic composites (WPCs) is a significant issue for outdoor applications. Nanosilica is widely used to enhance the ultraviolet (UV) aging resistance of composites. In this study, the effects of nanosilica (0%, 1%, 2%, 5%, and 10%) added into the shell of coextruded WPCs were investigated after 2500‐hour UV exposure. Discoloration, durability, degradation, and photooxidation of the composites were studied by colorimetry, mechanical testing, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X‐ray photoelectron spectroscopy (XPS). The samples with 2% nanosilica addition (the N2 samples) provided optimal color protection, showing the lowest ΔE* (color difference) and ΔL* (lightness) values in all samples. The surface of N2 samples was less oxidized after UV exposure as revealed by FTIR and XPS analysis, and showed fewer cracks in SEM images compared with controls and other samples. In addition, N2 samples provided best flexural properties. In summary, the addition of 2% nanosilica was most effective in protecting WPCs from UV degradation. Moreover, obtained results provide a theoretical development for adopting the nanosilica as a reinforcing agent in WPCs and applying coextruded WPCs in outdoors.     

The effect of chemical modification on the strength of wood and bonded wood joints

The effect of propionic, crotonic or methacrylic anhydride (MA) modification on the lab joint strength of monomer bonded veneer strips was investigated. Lap joints were formed by hot pressing veneers of modified wood with monomer in the presence of free radical initiator and bond strength was determined on an Automatic Bonding Evaluation System tensile tester. Test results indicated that chemical treatment improved bond quality between hydrophilic wood and hydrophobic monomer. Extremely strong bonds (wet and dry conditions) formed in the case of MA modified veneer strips. In addition, the effect of chemical modification on the mechanical properties of strips was also investigated. Chemical modification had a detrimental effect on the mechanical properties.     

The addition of clay on the mechanical properties of surface‐treated CF‐filled PA66 composites

Polyamide 66 (PA66) composites filled with clay and carbon fiber (CF) were prepared by twin‐screw extruder in order to study the influence of nanoparticle reinforcing effect on the mechanical behavior of the PA66 composites (CF/PA66). The mechanical property tests of the composites with and without clay were performed, and the fracture surface morphology was analyzed. The results show that the fracture surface area of the clay‐filled CF/PA66 composite was far smoother than that of the CF/PA66 composite, and there formed a tense interface on the CF surface after the addition of clay. The tensile and flexural strength of CF/PA66 composites with clay was improved. The impact strength decreased because of the high interfacial adhesion. In conclusion, the addition of clay favored the improvement of the higher interface strength and so had good effect on improving the tensile and flexural properties of the composites. Copyright © 2017 John Wiley & Sons, Ltd.     

钛酸酯偶联剂的结构对PVC/木质素复合材料性能的影响

本文采用钛酸酯系列偶联剂对造纸工业废渣──木质素磺酸盐进行处理，然后填充聚氯乙烯（PVC）制成复合材料．结果发现用钛酸酯类偶联剂处理的木质素磺酸盐，填充PVC体系，其拉伸强度随使用钛酸酯偶联剂不同，拉伸强度下降幅度不同，而冲击强度和伸长率都不同程度上升，尤以冲击强度的提高最为明显．     

Influence of the wood fibre filler on the internal recycling of poly(vinyl chloride)-based composites

The recycling of internal waste of poly(vinyl chloride) (PVC) and wood fibre-reinforced PVC composite was investigated and compared. Twenty extrusion-milling cycles were performed and the mechanical and thermal properties evaluated. This comparison provided evidence of the influence of the vegetable fibres on the thermo-mechanical degradation of the composite material. Up to five cycles, the composite properties remained stable. But after 10 cycles and especially at 20 cycles, the flexural strength increased, whereas the other mechanical properties remained almost constant. At the same time, a decrease of the degradation temperature revealed a deterioration of the molecular structure. The PVC properties remained constant, whereas a great increase in the impact strength was observed after 20 cycles without deterioration of the molecular structure. The different behaviours between the composite and the PVC were explained by the influence of the fibres, which accelerated the PVC degradation, characterized by dehydrochlorination followed by crosslinking reactions.     

The effect of wood extractives on the thermal stability of different wood species

This study compares the thermal stability of different wood species, which is an important factor for the production of wood–polymer composites (WPCs), and investigates the effect of extraction on thermal properties. The chemical composition of four wood species – Quercus alba, Pinus radiata, Eucalyptus grandis and Acacia cyclops – has been determined, as the species is expected to affect the thermal stability of wood. Subsequently, the hot-water (HW) extractives, ethanol/cyclohexane (E/C) extractives and both extractives were eliminated from the wood via Soxhlet extraction and the thermal stability of the wood determined with thermogravimetric analysis (TGA) under identical conditions. The results suggest that a higher cellulose and lignin content leads to better thermal stability of wood in different temperature regimes. In all cases, the removal of extractives improved the thermal stability of the wood. The effect of combined extractions was more pronounced than of an individual extraction and E/C-extraction caused less improvement in the thermal stability of wood than HW extraction. The degradation of the investigated wood extractives occurred at low rates over a broad temperature range. Pure cellulose exhibited superior thermal stability compared to wood, but differences were observed between the investigated wood species.     

Effect of sol-gel derived nano-silica and organic peroxide on the thermal and mechanical properties of low-density polyethylene/wood flour composites

The influence of nano-silica, synthesized and mixed with low-density polyethylene (LDPE) through a sol-gel process, on the thermal and mechanical properties of LDPE and LDPE/wood flour (WF) composites, prepared in the absence and presence of dicumyl peroxide, was investigated. Scanning electron microscopic (SEM) analyses show a uniform dispersion of silica nano-particles of size 10-50 nm in the matrix, and Fourier-transform infrared (FTIR) spectroscopic results indicated interaction between the nano-silica and the LDPE matrix, which seems to improve for samples prepared in the presence of dicumyl peroxide (DCP). WF and nano-silica, as well as the presence of DCP during sample preparation, substantially improve the thermal stability of the LDPE matrix. The tensile strength of the samples decreased with increasing wood flour content, while the tensile modulus substantially increased. The presence of nano-silica gave rise to lower values for both tensile strength and tensile modulus, while higher tensile strength (and an increase in tensile strength with WF content) is observed for samples prepared in the presence of DCP. The tensile modulus increases with increasing WF content, but is not substantially influenced by the presence of nano-silica or by sample preparation in the presence of DCP. The DMA results were in line with the tensile results.     

Effect of the melt flow index of an HDPE matrix on the properties of composites with wood particles

Composites of wood waste and high-density polyethylene (HDPE) resins and different melt flow index (MFIs) was development in this work. Therefore, it was possible to assess their effect on the mechanical, thermal, and morphologic properties of these composites. The formulations were prepared using a twin-screw extruder, and the MFI, tensile strength, flexural strength, and impact strength of the composites were analyzed. Additionally, the thermal properties were evaluated by differential scanning calorimetry (DSC). Finally, structural analyses using optical microscopy (OM) and scanning electron microscopy (SEM) were performed to assess the particles’ dispersion, distribution, and adhesion to the polymer matrix. The results indicated that composites from HDPE resins with a lower MFI yielded a better dispersion of the wood waste. During processing was observed, reduce the MFI and better dispersion of the polymer matrix, which positively influenced some of the mechanical properties analyzed in the study.     

The effects of a silane coupling agent on curing characteristics and mechanical properties of bamboo fibre filled natural rubber composites

The effects of a silane coupling agent on curing characteristics and mechanical properties of bamboo fibre filled natural rubber composites were studied. Scorch time, t₂ and cure time, t₉₀ of the composites decrease with increasing filler loading and with the presence of a silane coupling agent, Si69. Mooney viscosity also increases with increasing filler loading but at a similar filler loading shows lower value with the presence of Si69. The mechanical properties of composites viz tensile strength, tear strength, hardness and tensile modulus were also improved with the addition of Si69.     

聚氯乙烯/木纤维复合材料的研究Ⅰ.硬脂酸和ABS改性木纤维对复合材料力学性能的影响

为改善聚氯乙烯（PVC）和木纤维两者的界面亲合性，提高PVC／木纤维复合材料的机械力学性能，分别用硬脂酸和ABS来改性木纤维的表面，研究发现用硬脂酸处理木纤维可提高复合材料的拉伸强度，但对复合材料的冲击强度影响不大．ABS处理木纤维可同时提高复合材料的拉伸强度和冲击强度。本文也研究了改性剂用量和木纤维含量对复合材料力学性能的影响。     

The effects of cauliflower-like short carbon fibers on the mechanical properties of rigid polyurethane matrix composites

Stress concentration and weak interfacial strength affect the mechanical properties of short carbon fibers (CFs) reinforced polymer composites. In this work, the cauliflower-like short carbon fibers (CCFs) were prepared and the point was to illuminate the effects of fiber morphology on the mechanical properties of the CCFs/rigid polyurethane (RPU) composites. The results indicated that the surface structure of CCFs could increase the surface roughness of the fibers and the contact area between fibers and matrix, thereby promoting the formation of irregular interface. Compared with pure RPU and initial CFs/RPU composites, the strength and toughness of CCFs/RPU composites were simultaneously improved. The satisfactory performance was attributed to the special fibers structure, which played an anchoring role and consumed more energy during crack propagation.     

The influence of hydroxyapatite modification on the cross-linking of polydimethylsiloxane/HAp composites

Hydroxyapatite (HAp) was modified by the action of various hydrophobic agents based on silicon-containing compounds. The influence of the type of applied agent on the thermodynamic and kinetic parameters of the cross-linking of poly(dimethyl siloxane)/HAp composites was investigated. All the modified HAp particles became hydrophobic and these samples were used to synthesize the polysiloxane/hydroxyapatite composites (PDMS/HAp). The possible modes of interaction between the hydroxyapatite and hydrophobing agents were discussed. The most probable interaction between hydroxyapatite and the applied hydrophobing agents is hydrogen bonding. PDMS/HAp composites were formed directly in the cell of the DSC and cross-linking was investigated in situ. It was determined that the introduction of hydroxyapatite into polysiloxane matrices changed the enthalpy of cross-linking, as well as the activation energy of cross-linking and reaction order, while the introduction of modified HAp led to thermodynamic and kinetic parameters more similar to those of the cross-linking of unfilled elastomer.