Preliminary study of viscoelastic properties of MAPP-modified wood flour/polypropylene composites

Viscoelastic properties of maleated polypropylene （MAPP）-modified wood flour/polypropylene composites （WPC） were investigated by both a compression stress relaxation method and dynamic mechanical analyses （DMA）. Three wood to polymer ratios （40：60, 60：40, and 80：20） and five MAPP loading levels （0, 1, 2, 4 and 8%） were used to study their effects on the viscoelastic prop- erties of MAPP-WPC. The results show that： 1） higher wood to polymer ratio corresponds to higher stress relaxation levels for unmodified WPC. The modification with MAPP has an obvious effect on the stress relaxation of MAPP-WPC at higher wood to polymer ratios （60：40 and 80：20）, but almost no effect at the 40：60 wood to polymer ratio. The optimal MAPP loading level for the wood to polymer ratio of 60：40 appears at 1%; 2） the storage modulus reaches its maximum at a MAPP loading level of 1% for wood to polymer ratios of 40：60 and 60：40, while for the 80：20 wood to polymer ratio, a higher storage modulus is observed at higher MAPP loading levels, which is quite consistent with the stress relaxation results. The results suggested that a suitable loading level of MAPP has a positive effect on the viscoelastic properties of WPC at higher wood to polymer ratios. Excessive MAPP loading would have resulted in adverse effects.

Dielectric properties of Simon poplar wood flour/polypropylene composite at oven-dry state

Interfacial compatibility is a crucial factor to the performance of wood-plastic composites （WPCs）. Yet, so far, the coupling mechanisms of WPC have not been completely understood. In order to further clarify the interfacial coupling mechanism, the dielectric constant and dielectric loss factor of Simon poplar wood flour/polypropylene composites without additives at different wood contents were measured at oven-dry state, and parameters and thermodynamic quantities of the relaxation process were also analyzed and calculated. Consequently, an obvious relaxation process based on the reorientation of methanol groups in amorphous region of wood cell wall was observed exactly that its dielectric loss factor peak decreased with the decreasing wood content within the measured range of 50%-100%. With the trend of dielectric relaxation strength, the two changing trends both revealed that the existence of polypropylene could hinder reorientation of methanol groups. Following the decreasing wood contents, the effect of the hindrance on the dielectric properties turned obvious gradually. It elucidated that introduction of polypropylene caused the quantities of hydrogen bonds formed between each methanol group and the groups around it change. The same conclusion could be drawn from the analysis of thermodynamic quantities during the dielectric relaxation progress.

Dynamic-mechanical analysis and SEM morphology of wood flour/polypropylene composites

A study was conducted to investigate the effects of compatibilizers, including Maleic anhydride grafted polypropylene （MA-PP） and maleic anhydride grafted ethylene-propylene-diene copolymer （MA-EPDM）, on wood-flour/polypropylene （WF/PP） composites. WF/PP composites were prepared by direct extrusion profiles using a twin-screw/single-screw extruder system. DMA analysis showed that the loss factor of composites decreased and the storage modulus improved in the presence of MA-PP, which indicated much better interfacial adhesion between the PP matrix and wood flour filler than in the absence of compatibilizer. Morphological feature based on SEM observation showed that MA-PP and MA-EPDM improved the dispersion of the wood particles in the plastic matrix. MA-EPDM is a soft segment, although it improved the interfacial adhesion, storage modulus decreases with adding of MA-EPDM. As compatibilizer of wood-flour/polypropylene composites, both DMA analysis and SEM feature proved that MA-PP was superior to MA-EPDM.

Study on Water Resistance of Polydopamine Treatment Wood Flour/Polypropylene Composites

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.

Reinforcing effects of modified Kevlar~ fiber on the mechanical properties of wood-flour/polypropylene composites

Kevlar fiber （KF） is a synthesized product with strong mechanical properties. We used KF as a reinforcement to improve the mechanical properties of wood-flour/polypropylene （WF/PP） composites. KF was pretreated with NaOH to improve its compatibility with the thermoplastic matrix. Maleated polypropylene （MAPP） was used as a coupling agent to improve the interfacial adhesion between KF, WF, and PP. Incorporation of KF improved the mechanical properties of WF/PP composites. Treatment of KF with NaOH resulted in further improvement in mechanical strength. Addition of 3% MAPP and 2% hydrolyzed KF （HKF） led to an increment of 93.8% in unnotched impact strength, 17.7% in notched impact strength, 86.8% in flexure strength, 50.8% in flexure modulus, and 94.1% in tensile strength compared to traditional WF/PP composites. Scanning electron microscopy of the cryo-fractured section of WF/PP showed that the HKF surface was rougher than the virgin KF, and the KF was randomly distributed in the composites, which might cause a mechanical interlocking between KF and polypropylene molecules in the composites.

Properties of PEG/thermally modified wood flour/polypropylene (PP) composites

In order to improve the dimensional stability of wood-polymer composites, wood flour pre-treated by polyethylene glycol （PEG） at two different concentrations and then thermally treated at 140℃, was used as raw material to produce wood flour/poly- propylene （PP） composites at a wood content of 40%. The structure of modified wood flour was analyzed with a scanning electron microscope （SEM） and its effect on the physical and mechanical properties of wood flour/PP composites was evaluated. The SEM results indicated the ＂bulking＂ effect of PEG on wood flour, which resulted in reduced water uptake. The combination of PEG and heat treatment further improved the moisture resistance of the composites. However, PEG modification had a negative effect on the flexural modulus of rupture （MOR） and the modulus of elasticity （MOE）; whereas heat treatment partly compensated for this reduc- tion. For dynamic mechanical properties, PEG treatment decreased the storage modulus （E＇）. However, the heat treatment resulted in an increase orE＇ of the wood flour/PP composites, with the temperature of loss factor peaks shifting to a higher temperature.

Morphology, Thermal Behavior and Dynamic Rheological Properties of Wood Polypropylene Composites

Wood polymer composites (WPCs) were made with pine and polypropylene matrix (PP). The composites were produced by melt blending in a Brabender at 180°C. Characterization of the samples, with the aid of scanning electron microscopy supplemented by microscope photography, showed an improved dispersion of wood in the polymeric material in presence of polypropylene grafted with maleic anhydride (MAPP) or nanoclay. The use of the MAPP instead of clay seems to have enhanced the level of crystallinity in the composites for the same levels of wood loading and also accelerates the crystallization. Melt rheological measurements of neat PP and PP-wood composites were carried out at 180°C with an ARES Rheometer scientific mechanical spectrometer in oscillatory frequency. All the composites materials exhibit viscoelastic values greater than those for neat PP. The samples containing MAPP as comptabilizer show the higher Newtonian viscosity, however, the addition of a small concentration of nanoparticles like nanoclays does not improve the resulting melt viscoelastic behavior of the composite.

Effect of maleic anhydride grafted styrene-ethylene-butylene-styrene （MA-SEBS） on impact fracture behavior of polypropylene / wood fiber composites

MA-SEBS 作为 compatibilizer；影响修饰词被合并到聚丙烯 / 木头纤维(PP/WF ) 提高接口粘附；影响力量合成。PP/WF composites 的影响破裂行为上的 MA-SEBS 内容的效果被学习。有 8% MA-SEBS 的 composites 的影响性质到达了最大的价值。并且到 10% 的 MA-SEBS 内容的进一步的增加没改进破裂坚韧，但是由直接存储器存取分析改进 composites 的僵硬。这被归因于改进 PP/WF 粘附。因为 MA-SEBS 内容是超过 8% ， PP 的分子相互作用；WF 被期望到比更低的 MA-SEBS 强壮的大部分。扫描电子显微镜学(SEM ) 被执行分析影响破裂表面；为木头表面显示出一种更强壮的亲密关系。

Creep Behaviour of Wood Flour/Poly(vinyl chloride) Composites

The experimental creep data were focused on wood-flour （WF）/poly vinyl chloride （PVC） composites with the variations in additive concentrations of wood flour, silane coupling agent, organomodified montmorillonite （OMMT） and nano-cacium carbonate （nano-CaCO3）. Their effects were analyzed using the Four-element Burger Model incorporating microscopic mechanisms. Total creep strain was low with increasing WF while elastic strain was high and plastic flow strain was low in modeling. Modification of WF with silane was beneficial to creep resistance, so did adding low ratio of OMMT （1.5 wt%） and nano-CaCO3 in composites. Thus, it was effective in reducing creep either by stiffening the PVC matrix using rigid nano-particles or by improving their adhesion with resin. However, superfluous quantity of any additament did not benefit the improvement owing to either earlier destruction of their agglomerates or stress-concentrated cracks in the over-incrassated interface.

Microwave Irradiation Treatment of Wood Flour and Its Application in PVC-Wood Flour Composites

The technique of microwave irradiation induced free radical bulk- polyaddition reactions in porous wood flour was used to modify wood flour. The behaviors of the modified wood flour under microwave irradiation, such as thermal stability and moisture sorption properties, were studied. A kind of semiinterpenetrating polymer network wood four （Semi-IPN-WF） can be formed through polymerization of MMA in the porous wood flour by microwave irradiation, and the thermal decomposition temperature of the semi-IPN-WF is considerably increased. PVC/Semi-IPN-WF composites were prepared by melt mixing in double rolls, which exhibit improved rheological properties, lower water sorption properties and outstanding mechanical performances.

Mechanical properties of wood flour/recycled-thermoplastic-blends composites

The mechanical properties of composites prepared from wood flour and thermoplastic blends were investigated. Thermoplastic mixtures of polypropylene (PP) and high-density polyethylene (HDPE) and polystyrene (PS), virgin or recycled, were mixed with wood flour in a high speed blender and then extruded by a specially designed twin/single screw extruder system to form wood-flour/thermoplastic-blends composites (WTBCs). Comparative studies were made to evaluate the effectiveness of the two modification methods of the thermoplastic blends, the one of the addition of maleic anhydride grafted styrene-ethylene-butylene-styrene block copolymer (SEBS-g-MAH) as compatibilizer and the other of blend grafting of maleic anhydride (MAH) using dicumyl peroxide (DCP) as initiator by reactive extrusion. The results showed that the impact properties of WTBCs using SEBS-g-MAH as compatilizer were better improved than that of the blend grafting. However, adverse results were observed on the tensile and flexural properties of the corresponding WTBCs. The mechanical properties of WTBCs prepared from recycled plastic blends were poorer to some extent than that from virgin plastic blends in general, especially in elongation break. The morphology of WTBCs breaking section was analyzed by scanning electron microscopy (SEM) and the results showed that a good interfacial adhesion between wood flour and polymer matrix was observed with both of the two modification methods. However, by blend grafting of adding DCP as initiator and MAH as monomer, a better interfacial bonding between wood and plastic matrix was obtained than that of the addition of SEBS-g-MAH. Blend grafting can be considered as a potential way of increasing the interfacial compatibility of different plastics and between plastic blends and wood.

Chemical characterization of smoke from the production process of wood-plastic composites

The chemical composition of unpleasant smell, emitted from the production process of wood-plastic composites using Manchurian ash sawdust （Fraxinus mandschurica Rupr.） and polypropylene powder as the raw material, was investigated. Wood sawdust and polypropylene powder were subjected to heat treatment to 290℃ during 8 min （the conditions were similar to those employed on an industrial scale）. The emitted compounds were collected and analyzed by gas chromatography-mass spectrometry （GC-MS）. The analytical results showed that the unpleasant smell was emitted from the pyrogenation of wood sawdust rather than from the polypropylene powder. Nine types of compounds （hydrocarbons, ethers, phenols, aldehydes, ketones, alcohols, acids and their derivatives, furan and its derivatives, and nitrogen-containing compounds） were collected in the gas phase during heating. Among those 126 components detected by GC-MS, 112 compounds were identified.

Effect of Wood Variables on the Properties of Wood Fiber-Polypropylene Composites

The effect of wood species (Chinese fir and Poplar), wood fiber content (10%, 25%, 40%) and wood fiber sizes (16 to 32 mesh, 32-65 mesh, above 65 mesh) on the properties of the wood fiber-Polypropylene composites were studied in this paper. The results indicate that the effect of wood fiber content and size in composite were more important than that of chosen wood species. Compared with polypropylene without wood fiber, the flexural strength of the composites increased when adding wood fiber into polypr...

Effect of Wood Particle Size on the Properties of Wood/Polypropylene Composites Ⅰ:Mechanical Properties

The mechanical properties of wood powder/polypropy!ene composites with different wood particle sizes and wood species have been studied. All of the wood particie sizes increased the E-modulus of the composites. Tensile tests showed that wood partide sizes had a negative effect on the elongation at break and the tensile strength of the composites has been improved when wood particle sizes were be(ow 150 μm (below 100 mesh). For the impact tests, the wood partide sizes had a negative effect, but the MDF f...

Dynamic Mechanical Properties of Wood Powder /Polypropylene Composites

The dynamic mechanical properties of wood powder/polypropylene composites with different wood content treated and untreated with the compatibilizer have been studied. It has been found that addition of wood powders and the compatibilizer can both improve the viscoelasticity of composites. Glass transition temperature (Tg) of appropriate wood powder-filled composites decreased. The value for the storage modulus (G') increased gradually with increasing wood powder content. The addition of the compatibiliz...

不同聚乙烯基塑木复合材料的性能

采用注塑工艺制备高密度聚乙烯(HDPE)基、低密度聚乙烯(LDPE)基及HDPE、LDPE混合基塑木复合材料(WPC),同时制备了纯HDPE及LDPE试样,对比研究了不同试样的吸水率、吸水尺寸稳定性、受热尺寸稳定性、耐冷热循环性、抗低温冻融性及抗冲击性能。结果表明,纯塑料的吸水率及吸水后尺寸变化率均较低,但是,受热后正反面尺寸变化相差较大,冷热循环后尺寸变化较大;当形成WPC后,试样的吸水率及吸水后尺寸变化率显著升高,其中,HDPE与LDPE混合基体的WPC的吸水率最高,其值为1.57%,宽度和厚度尺寸变化率分别为0.11%和1.08%;受热后,正反面尺寸变化率差值减小,耐冷热循环能力得到显著提升;HDPE及其WPC的弯曲强度与LDPE及其WPC相比较高,但是,后者的抗冻融性能及抗冲击性能与前者相比较好。

多功能磷酸酯共聚物阻燃HDPE木塑复合材料的性能

以1-氧基磷杂-4-羟甲基-2,6,7-三氧杂双环[2.2.2]辛烷、多聚磷酸、1,4-丁二醇二缩水甘油醚、双酚A型环氧树脂和三聚氰胺为原料合成磷酸酯共聚物,以其为阻燃剂对高密度聚乙烯(HDPE)/木粉(WF)木塑复合材料进行阻燃改性,并评价了阻燃剂含量对复合材料阻燃性能、力学性能和热性能的影响。结果表明:集酸源、气源和碳源为一体的磷酸酯共聚物的热稳定性明显高于常规磷系阻燃剂,阻燃剂含量为20%(w)时,HDPE/WF复合材料的垂直燃烧等级达到UL 94 V-0级,极限氧指数高达31.5%,残炭量提高了21.5%(w);随阻燃剂含量增加,复合材料的拉伸强度呈先上升后下降的趋势。

不同聚乙烯基塑木材料水热老化性能分析

以高密度聚乙烯、低密度聚乙烯及两者混合物为基体,以木粉为填料,制备塑木复合材料(WPC),对比研究了3种WPC在60和90℃水热环境中的老化性能。结果表明,所有WPC在温度为60或90℃条件下的吸水率及尺寸变化率均随浸泡时间的延长而增加,并且,呈现先快速增加、后逐渐缓和的趋势,混合基体WPC的吸水率和尺寸变化率在同样的时间段均高于其他2种WPC;经水热老化后,所有WPC的拉伸强度、弯曲强度和冲击强度均有下降,当温度为60℃时,LDPE基的拉伸强度、弯曲强度及冲击强度下降均较显著,保持率分别为96.22%、93.76%和92.66%;当温度为90℃时,LDPE基的拉伸强度及冲击强度下降均较显著,保持率分别为89.44%和87.20%,HDPE/LDPE混合基WPC弯曲强度下降较显著,保持率为88.76%;扫描电子显微镜照片显示,水热老化使WPC的内部结构发生了一定程度的破坏,90℃下破坏程度较显著。