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.

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.

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.

Rheological and mechanical properties of wood fiber-PP/PE blend composites

For evaluation of the rheological and mechanical properties of highly filled wood plastic composites （WPCs）, polypropylene/polyethylene （PP/PE） blends were grafted with maleic anhydride （MAH） to enhance the interfacial adhesion between wood fiber and matrix. WPCs were prepared from wood fiber up to 60 wt.% and modified PP/PE was blended by extrusion. The rheological properties were studied by using dynamic measurement. According to the strain sweep test, the linear viscoelastic region of composites in the melt was determined. The result showed that the storage modulus was independent of the strain at low strain region （〈0.1%）. The frequency sweep resuits indicated that all composites exhibited shear thinning behavior, and both the storage modulus and complex viscosity of MAH modified composites were decreased comparing to those unmodified. Flexural properties and impact strength of the prepared WPCs were measured according to the relevant standard specifications. The flexural and impact strength of the manufactured composites significantly increased and reached a maximum when MAH dosage was 1.0 wt%, whereas the flexural modulus after an initial decreased, also increased with MAH dosage. The increase in mechanical properties indicated that the presence of anhydride groups enhanced the interracial adhesion between wood fiber and PP/PE blends.

Effects of two modification methods on the mechanical properties of wood flour/recycled plastic blends composites: addition of thermoplastic elastomer SEBS-g-MAH and in-situ grafting MAH

The effect of maleic anhydride grafted styrene-ethylene- buty-lene-styrene block copolymer （SEBS-g-MAH） and in-situ grafting MAH on mechanical, dynamic mechanical properties of wood flour/recycled plastic blends composites was investigated. Recycled plastic polypro-pylene （PP）, high-density polyethylene （HDPE） and polystyrene （PS）, were mixed with wood flour in a high speed blender and then extruded by a twin/single screw tandem extruder system to form wood flour/recycled plastic blends composites. Results show that the impact properties of the composites were improved more significantly by using SEBS-g-MAH compatibilizer than by using the mixtures of MAH and DCP via reactive blending in situ. However, contrary results were ob-served on the tensile and flexural properties of the corresponding com-posites. In General, the mechanical properties of composites made from recycled plastic blends were inferior to those made from virgin plastic blends, especially in elongation break. The morphological study verified that the interfacial adhesion or the compatibility of plastic blends with wood flour was improved by adding SEBS-g-MAH or in-situ grafting MAH. A better interfacial bonding between PP, HDPE, PS and wood flour was obtained by in-situ grafting MAH than the addition of SEBS-g-MAH. In-situ grafting MAH can be considered as a potential way of increasing the interfacial compatibility between plastic blends and wood flour. The storage modulus and damping factor of composites were also characterized through dynamic mechanical analysis （DMA）.

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.

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.

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.

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.

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.

马来酸酐接枝PP/PE共混物及其木塑复合材料

通过聚丙烯(PP)与聚乙烯(PE)机械混合来模拟废旧塑料混合物,利用马来酸酐(MAH)对PP/PE混合物进行接枝改性,然后以接枝共混物作为基体与木纤维复合制备木塑复合材料。通过对比接枝前后的红外光谱图,证明MAH已成功接枝在PP/PE共混物上。力学测试结果显示:基体经过接枝改性后,复合材料的弯曲强度和无缺口冲击强度均大幅度升高,当MAH用量为1%时,弯曲强度提高了50.4%,无缺口冲击强度提高了90.8%,而以废旧塑料为原料制备的复合材料的弯曲强度和无缺口冲击强度分别提高40.2%和53.4%。微观相形态分析表明:通过接枝改性不仅改善了PP/PE共混体系的相容性,同时也显著改善了木纤维与PP/PE共混物之间的界面结合状况,因而宏观上表现为力学性能提高。这表明,共混接枝改性方法可能是利用混合废旧塑料制备高性能木塑复合材料的一条可行途径。

不同改性剂对PP/木粉复合材料性能的影响

研究了苯甲酸(BA)、硬脂酸(SA)、甲苯-2,4-二异氰酸酯(TDI)对聚丙烯/木粉复合材料的改性效果。结果表明,木粉经改性剂处理后,表面极性减弱,与聚丙烯的界面张力降低,相容性提高;所有改性剂均可提高复合材料的拉伸强度、冲击强度以及熔体流动性能,但对弯曲强度影响不大。用TDI/SA复合处理木粉,复合材料的综合性能最好。扫描电镜(SEM)分析表明,木粉经过处理后,木粉与聚丙烯间界面较模糊。

EVA改性PP/杨木粉复合材料的制备及性能研究

以PP为基体,采用热压成型的方法制备PP/杨木粉复合材料。通过转矩流变、维卡耐热、SEM等分析方法研究了偶联剂含量、2种热塑性弹性体及其含量对复合材料流变、耐热、力学性能的影响。结果显示,0.5份的偶联剂可以提高木粉30份体系的拉伸强度及缺口冲击强度。EVA的改性效果显著,试样EA10的拉伸强度和缺口冲击强度分别为31.4MPa和7.94kJ/m2,较WF30分别提高23.62%和56.92%。SEM断面观察发现,试样的EA10基体连续性良好,大量木纤维在基体中断裂,撕裂区域较多,说明材料的韧性得到明显改善。

APP对木粉-HDPE复合材料阻燃和力学性能的影响

以聚磷酸铵(APP)对木粉-HDPE复合材料(WF-HDPE)进行阻燃处理,用锥形量热仪系统评价复合材料的阻燃性能,并进行等温燃烧反应动力学分析,用万能力学试验机进行静态力学试验。结果表明,在35 kW/m2热辐射流量下,APP添加量达到15%时,WF-HDPE燃烧热释放速率(RHR)峰值和总热释放量(THR)均降低约50%、成炭率提高150%,表现出显著的阻燃作用;可用动力学模型ln(1-α)=-kt+C描述WF-HDPE的等温燃烧反应,APP的加入使反应速率常数k降低、半衰期延长。APP对WF-HDPE的冲击性能有显著的不利影响,但能改善刚性,对弯曲强度和拉伸强度影响不大。综合阻燃性能与力学实验结果,APP的适宜添加量为15%左右。

不同相容剂对PP/木粉复合材料力学性能的影响

研究了3种相容剂和3种偶联剂分别在单独使用和配合使用情况下对PP/木粉(质量比50/50)复合材料力学性能的影响。相容剂PP-g-MAH、PE-g-MAH、SBS-g-MAH单独使用发现:SBS-g-MAH使材料综合性能最好,PE-g-MAH对冲击强度提高明显。硅烷偶联剂HP-172在提高复合材料的冲击强度和拉伸强度方面较好,HP-174对弯曲性能改善较好,钛酸酯偶联剂NDZ-201仅对弯曲模量有所改善,而对其它性能改善不大。相容剂与偶联剂共同使用具有协同效应,其中HP-174与SBS-g-MAH并用效果最好,使各项力学性能都有提高。

PP基木塑复合材料的制备及性能研究

以PP为基体,采用热压成型方法制备木塑复合材料。通过X射线衍射和SEM研究了木粉含量、偶联剂改性对复合材料结晶、流变、力学性能的影响。结果表明,木粉的加入会抑制-βPP晶型的生成,10份木粉可能有助于(040)晶面的生长。随着木粉含量的增加,复合材料的拉伸强度有所提高,而冲击性能明显降低。加入0.5份铝酸酯偶联剂时,-αPP的特征峰(130)以及主要晶面(010)(、040)的衍射强度均有所增加,缺口冲击强度为6.25kJ/m2,较未添加铝酸酯偶联剂的复合材料提高23.52%,SEM结果也显示出同样的趋势;同时,材料的加工性能也有所改善。

PP基木塑复合材料的热失重分析

研究了几种聚丙烯(PP)基木塑复合材料的热失重性能,并用显微镜观察了其微观结构。结果表明,实验用的几种木粉在140～165℃之间开始失重,而制得的PP基木塑复合材料的起始失重温度要比木粉高5～15℃,木粉和木塑复合材料在350℃上下出现了失重速率的峰值,到500～600℃质量基本上不再变化。显微镜观察显示,木粉与树脂之间有较好的分散效果。