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）.

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.

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.

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.

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.

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.

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.

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.

聚丙烯/木粉复合材料的制备及性能

分别采用聚丙烯的固相接枝共聚物和熔融接枝共聚物作为聚丙烯/木粉复合材料的界面改性剂,研究两种多单体接枝共聚物用量对复合材料界面结构、拉伸性能、弯曲性能、抗冲击性能等的影响,并根据拉伸性能数据计算复合材料的界面黏结强度。结果表明:两种多单体接枝共聚物均能有效地提高复合材料的力学性能,并维持良好的热稳定性;随多单体接枝共聚物用量的增加,复合材料的力学性能提高,当多单体接枝共聚物用量为5 phr时,复合材料的界面相容性较稳定,力学性能最佳,界面黏结强度参数从2.56升至3.50以上,表明复合材料具有较强的界面黏结强度。

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。

木粉预处理对PP/WF复合材料力学性能的影响

随着环境的恶化和森林资源的匮乏,木塑复合材料等代木材料愈显重要。界面相容性差导致力学性能不足是限制木塑复合材料应用的重要因素。为了提高木塑复合材料的力学性能,分别采用干燥、汽蒸、水煮等方式处理木粉,研究这三种处理方式对接枝共聚物增容的聚丙烯/木粉复合材料界面相容性以及拉伸性能、弯曲性能、冲击性能等力学性能的影响;并根据拉伸性能计算复合材料的界面结合强度。结果表明,汽蒸、水煮两种处理方式有助于进一步提高该复合材料的界面相容性及其力学性能;水煮处理比汽蒸和干燥处理更有效地提高复合材料的力学性能。干燥、汽蒸、水煮三种处理复合材料的界面结合强度参数B值分别是3.45、3.48和3.54,均高于未增容聚丙烯/木粉复合材料的2.72,表明复合材料具有较强的界面结合强度。

新型胶合板水性木质复合覆面填补材料的制备和评价

探究了基于木纤维粒径/木粉种类差异填充胶合板缝隙的复合腻子配方、影响因素、性能评价,致力于胶合板素板表面缝隙填充、平整度调控的技术开发。采用单因素条件探讨了温度、木粉种类、木纤维目数等对腻子性能的影响。结果表明:添加木纤维的腻子填充材料除表干时间略高于未添加木纤维的对照组外,耐磨性、干强度、湿强度、相容性、稳定性相比于未添加木纤维的腻子填充材料均有了明显提高。在木纤维目数一致的情况下,添加木纤维的种类不同也会对腻子的各项性能产生影响。其中湿强度与粗糙度优劣排列依次是:桉木粉、杨木粉、杂木粉、松木粉、竹粉;干强度优劣排列依次是:桉木粉、杂木粉、杨木粉、松木粉、竹粉;耐磨性优劣排列依次是:杨木粉、松木粉、杂木粉、桉木粉、竹粉。木纤维的种类对腻子的表干时间、相容性、稳定性没有显著影响。

3D打印工艺对木粉/聚乳酸材料性能的影响

采用熔融沉积法(FDM)3D打印工艺制作木粉(WF)与聚乳酸(PLA)质量比为3∶100的WF/PLA复合材料,研究了打印工艺参数对WF/PLA复合材料力学性能的影响,确定了最佳打印工艺条件,然后,在最佳条件下,打印WF与PLA质量比为11∶100的WF/PLA复合材料,并且,将该材料的性能与FDM 3D打印PLA试样进行了对比。结果表明,当打印层厚度为0.1 mm、打印温度为220℃、打印速度为50 mm/s、填充密度为100%、沉积角度为0时,WF/PLA复合材料的力学性能最佳。在该工艺条件下,WF与PLA质量比为11∶100的WF/PLA复合材料的拉伸强度、拉伸模量、弯曲强度、弯曲模量和冲击强度分别为纯PLA的89.61%、97.56%、82.86%、92.40%和95.04%,与纯PLA相比,复合材料的表面润湿性能较好,吸水率显著增大。

柠檬酸三丁酯改性WF/PLA复合材料的制备及性能

以聚乳酸为基体材料、木粉为增强材料、柠檬酸三丁酯为增容剂,采用熔融共混挤出工艺制备了木粉/聚乳酸(WF/PLA)复合材料,分析了柠檬酸三丁酯(TBC)的添加量对复合材料力学性能、流动性、热性能、吸水性等性能的影响。结果表明,TBC提高了复合材料的力学性能,当TBC的含量为4%时,复合材料的拉伸强度及断裂伸长率达到最大,其值分别为36.84 MPa、2.7%,与未添加TBC相比,分别提高了44.0%、53.4%。添加4%的TBC后,复合材料的吸水率降低,并且,复合材料达到饱和吸水的时间较长。除此以外,TBC还有效地改善了复合材料的界面相容性及流动性,降低了复合材料的熔融温度Tm。