Effect of chemical modification on the properties of wood/polypropylene composites

对以铝酸酯为偶联剂对木粉进行表面改性处理后制备的木粉/聚丙烯复合材料的力学性能和形态学特征进行了研究。结果表明:铝酸酯偶联剂可以增加木塑复合材料的抗冲击强度,但会对复合材料的抗拉强度和抗弯强度造成负面的影响。对木塑复合材料的动态力学性能和微分扫描热量分析研究表明,以铝酸酯作为偶联剂,对木塑复合材料的储存模量和损失模量有少许增加,同时可降低材料的熔点和熔解热。利用扫描电镜观察木塑复合材料的木材与塑料界面发现,经铝酸酯处理过的木材与聚丙烯复合界面之间具有更好的相容性。这些研究结果表明,在木塑复合材料制造过程中利用廉价的铝酸酯作为木材化学改性剂,对改善复合材料的性质同样起作良好的作用。图6 表2 参16。     

Improvement in compatibility and mechanical properties of modified wood fiber/polypropylene composites

To improve the interfacial compatibility between wood fibers and polypropylene and the toughness of wood-fiber/polypropylene composites, maleic anhydride grafted polypropylene (PP-g-MAH) and maleic anhydride grafted styrene-ethylene-butadiene-styrene copolymers (SEBS-g-MAH) were used as modifiers. Mechanical properties of wood-fiber/polypropylene (WF/PP) composites were improved when PP-g-MAH or SEBS-g-MAH was added. When either of these copolymers was added, the composites had better interfacial compatibility than the unmodified composite. This was verified by scanning electron microscope (SEM) observations and dynamic mechanical analysis (DMA). The mechanical properties of the composites were significantly improved because of the good interfacial bonding between wood fibers and polypropylene when PP-g-MAH and SEBS-g-MAH were added. __________ Translated from Journal of Beijing Forestry University, 2007, 29(2): 133–137 [译自: 北京林业大学学报]     

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 properties 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.     

MA-SEBS对木纤维/聚丙烯复合材料冲击断裂行为的影响(英文)

马来酸酐接枝苯乙烯-乙烯-丁烯-苯乙烯(MA-SEBS)用作聚丙烯/木纤维复合体系的界面相容剂及冲击改性剂,来提高其界面粘接及冲击强度。研究了MA-SEBS含量对PP/WF复合材料冲击断裂行为的影响,当MA-SEBS含量达到8%时,冲击性能达到了最大值,进一步增加到10%并未提高其断裂韧性,但动态热机械分析(DMA)表明复合材料刚性的提高,这归因于PP/WF界面的改善,当MA-SEBS超过8%,聚丙烯与木纤维分子间的相互作用增强。扫描电子显微镜(SEM)分析了样品的断裂表面,表明木纤维与聚丙烯表面强烈的界面粘结。图5表1参11。     

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

MA-SEBS as compatibilizer and impact modifier was incorporated into Polypropylene/Wood Fiber （PP/WF） to enhance interface adhesion and impact strength of the composite. The effect of MA-SEBS content on the impact fracture behavior of PP/WF composites was studied. The impact properties of composites with 8% MA-SEBS reached the maximum value. And further increasing of MA-SEBS content to 10% did not improve the fracture toughness, but improved the stiffness of composites by DMA analysis. This was attributed to the improved PP/WF adhesion. As the MA-SEBS content is more than 8%, the molecule interaction of PP and WF was expected to much stronger than lower MA-SEBS. Scanning electron microscopy （SEM） was performed to analyze the impact fracture surface and showed a stronger affinity for the wood surfaces.     

Microscopic structure and properties of wood-based foaming composites

In order to reduce the density of wood-based composites without causing a deterioration of their mechanical properties, we studied the process of manufacturing wood-based composites. A combination of polymer foaming technology and flat hot-pressing technology was used. The microscopic structure of the various wood-based composites was analyzed with a scanning electron microscope (SEM). Modulus of rupture (MOR), modulus of elasticity (MOE), impact strength, and thickness expansion rate of water sorption (TS) were all measured. The results showed that fibers loosely interweave, and fibers had been connected by micropore. They also showed that spaces between fibers had big micropore structure. MOR, MOE and impact strength were the highest among three levels of ratio. When the total content of resin and foaming agent were 20% by weight, TS was higher. A hot-pressing temperature of 120°C was optimal. At the low temperatures of 80°C, the foaming process was uncompleted. At a higher temperature, micropores burst at a certain pressure. Based on the variance analysis and maximum difference analysis, a significance test shows that the optimum conditions for the total content of resin and foaming agent is 20% by weight, with a hot pressing temperature of 120°C for 15 min. Under these conditions, the properties of wood-based foaming composites all achieved the industry standard. __________ Translated from Journal of Beijing Forestry University, 2007, 29(3): 154–158 [译自: 北京林业大学学报]     

Effect of the amount of lignin on tensile properties of single wood fibers

Chemical components are the main factors affecting the mechanical properties of wood fibers. Lignin is one of the main components of wood cell walls and has a critical effect on the mechanical properties of paper pulp and wood fiber based composites. In this study, we carried out tensile tests on single mature latewood tracheids of Chinese fir (Cunninghamia lanciolata (Lamb.) Hook.), using three different delignified treatment methods to obtain different amounts of lignin. We applied single fiber tests to study the effect of the amount of lignin on mechanical tensile properties of single wood fibers at the cellular level. The results show that in their dry state, the modulus of elasticity of single fibers decreased with the reduction in the amount of lignin; even their absolute values were not high. The amount of lignin affects the tensile strength and elongation of single fibers considerably. Tensile strength and elongation of single fibers increase with a reduction in the amount of lignin.     

The effect of isolation method on the chemical structure of residual lignin

Two methods are used for the isolation of residual lignin: acidolytic and enzymatic hydrolysis. Recently a two-step procedure that is a combination of enzymatic and acidic hydrolyses was proposed. In this paper, the structures of residual lignins isolated by these three methods are compared. Enzymatic hydrolysis gave lignin with the highest yield (83%); however, it contained high amounts of carbohydrates and protein. The molar mass of enzymatic lignin was the highest, indicating that no cleavage of lignin occurred. Acidolysis gave a significantly lower lignin yield (40%), but this lignin was practically free from impurities. The -aryl ether and lignin-carbohydrate linkages cleaved during the isolation, which was manifested in the decreased molar mass of the lignin as well as in increased phenolic hydroxyl group content. The new two-step isolation procedure gave properties between the preparations of enzymatic and acidolytic hydrolyses. The lignin yield was high (78%), but it contained some impurities, although less than the enzymatic lignin. The lignin-carbohydrate linkages cleaved to some extent, but the -aryl ether linkages remained intact.Y. Sun also affiliated with the Pulp and Paper Research Institute of Canada (PAPRICAN), Pulp and Paper Research Centre, McGill University.     

The effect of lignin on the bending properties and fixation by cooling of wood

To clarify the effects of lignin on the fixation of bending deformation by cooling, cooling set for delignified woods with various lignin residues were investigated to compare with mechanical and dynamic viscoelastic properties. Bending tests showed that steep reductions occurred in the modulus of elasticity and modulus of rupture with delignification during the initial stage of delignification. The dynamic viscoelastic measurements revealed that the peak temperature of tan δ due to micro-Brownian motion of lignin was reduced with delignification, and the peak disappeared in the temperature range of 5°–100°C for the specimens that had lost more than 21% of their weight. On the other hand, no clear change in residual set was found in the range of 0%–15% of weight loss in spite of a marked reduction in lignin content. Subsequently, set decreased steeply for the specimens delignified beyond 15% of weight loss. It was suggested that cooling set is not determined solely by lignin content but is influenced by changes in the quality of lignin due to delignification. Lignin quality affects the balance of the elastic potential to recover from deformation and its viscosity, which is an indication of resistance against flow. Part of this report was presented at the 57th Annual Meeting of the Japan Wood Research Society, Hiroshima, August 2007     

木纤维PP/PE共混物复合材料的流变和力学性能(英文)

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.     

炭含量对竹炭/高密度聚乙烯复合材料电磁屏蔽和力学性能的影响

为了探究竹炭含量对竹炭基复合材料性能的影响,以竹炭(BC)和高密度聚乙烯(HDPE)为原料,采用熔融挤出-模压成型工艺制备竹炭/高密度聚乙烯(BC/HDPE)复合材料,通过对不同竹炭含量的BC/HDPE复合材料进行测试,研究炭含量对复合材料力学性能、热性能、电磁屏蔽性能以及微观结构的影响.结果表明,竹炭对BC/HD...     

不同改性剂对木塑复合材料性能的影响研究

采用木材纤维分别与PE、PS、ABS、SAN四种塑料制成木塑复合材料，根据物理力学性能的检测，研究了不同改性剂对木塑复合材料性能的影响。结果表明：加入改性剂能改善木材纤维与所用塑料交接性能，改性剂可以提高复合材料的力学强度；不同的改性剂对复合材料的性能产生不同的影响，异氰酸酯胶改性效果比较好。木塑复合材料既保持了木质材料原来的优良品质，又具有塑料的一些特性，其防水性、尺寸稳定性、力学强度等指标均有较大改善。图5参6。     

The effect of mineral fillers on the thermal properties of wood-plastic composites

Abstract

The thermal properties of wood-plastic composites with five different mineral fillers were studied. The tested mineral fillers were calcite (CaCO₃), two different qualities of wollastonite, soapstone, and talc. The amount of wood, mineral, and plastic (polypropylene) was kept constant. Only the mineral type has been changed during the tests. The thermal behavior of the samples was studied by using a differential scanning calorimeter, a thermogravimetric analyzer and by determining the heat build-up. The analyzed properties were compared with a reference sample made without adding any minerals. The results show that the addition of mineral fillers does not remarkably change the thermal stability of composites. All the studied mineral fillers except soapstone had a small effect on the heat build-up.     

Preliminary study of the effects of EVA coupling agents on properties of wood-plastic composites

As a hot-melt adhesive, ethylene-vinyl-acetate (EVA) has been used in many industrial applications. But studies of the application of EVA in wood-plastic composites (WPC) are relatively few, so we have investigated the proposition of whether EVA is a suitable coupling agent for WPC or not. The results show that EVA with 8% VA is not a suitable coupling agent, because it reduces the mechanical properties of WPC without any significant effect on its physical properties. With an increase in the amount of wood powder, the mechanical properties of WPC decrease and the ability of water absorption of WPC increases.     

氧等离子体改性酶解木质素/杨木纤维复合材料热压工艺研究

采用响应面法优化了氧等离子体改性酶解木质素/杨木纤维复合材料的热压工艺参数。结果表明,纤维含水率和热压温度对复合材料的物理力学性能有显著影响。优化后的热压工艺参数范围为:热压温度205～210℃,纤维含水率17%～20%,热压时间63～68 s/mm。     

SEBS-g-MAH和原位接枝MAH对木粉/废旧塑料混合物复合材料力学性能的影响研究

由聚丙烯（PP）、高密度聚乙烯（HDPE）和聚苯乙烯（PS）组成的混合废旧塑料与木粉经高速混合机混合后,采用双螺杆/单螺杆串联挤出机组制备了木粉/混合废旧塑料复合材料。探讨了马来酸酐接枝苯乙烯-乙烯/丁烯-苯乙烯嵌段共聚物（SEBS-g-MAH）和原位接枝马来酸酐（MAH）对木粉/混合废旧塑料复合材料力学性能的影响。结果表明,与使用MAH和DCP的原位反应共混相比,SEBS-g-MAH显著提高了复合材料的抗冲击性能,但对拉伸和弯曲性能的改善不如原位反应共混显著。总的来说,混合废旧塑料制备的复合材料的力学性能要低于纯塑料混合物制备的复合材料,尤其是拉伸断裂伸长率。微观形态研究表明,添加SEBS-g-MAH和原位接枝MAH均可提高木粉与塑料混合物之间的界面相容性,但与添加SEBS-g-MAH相比,原位接枝MAH能更好的改善PP、HDPE、PS与木粉之间的界面结合。原位接枝MAH可被看作是一种改善木粉与塑料混合物间界面相容性的有效途径。此外,采用动态力学分析（DMA）进一步表征了复合材料的储能模量和阻尼因子。     

羟甲基脲改性氧化石墨烯材料的制备及吸附Cu2+和Ni2+的性能

针对当前氧化石墨烯材料存在的吸附后固液分离困难的问题,采用化学接枝法制备了一种新型的氧化石墨烯/羟甲基脲复合材料(UF-GO),并用于水中重金属离子的去除。探讨了pH、时间及初始浓度对重金属离子去除能力的影响。结果表明:UF-GO复合材料保持了GO对重金属离子优异的吸附能力,吸附过程符合Langmuir吸附等温式,室温下对Cu²⁺、Ni²⁺的饱和吸附容量分别为96.9、94.1 mg·g^-1。在循环利用8次后,UF-GO复合材料对Cu²⁺、Ni²⁺两种离子的吸附容量仍保持有初次吸附容量的60、58%,表明UF-GO复合材料的回用性能较好,且能稳定存在。与GO相比,UF-GO复合材料吸附后的固液分离更加方便,有望成为一种具有较好应用前景的吸附材料。     

Formation and chemical structures of acid-soluble lignin II: reaction of aromatic nuclei model compounds with xylan in the presence of a counterpart for condensation,and behavior of lignin model compounds with guaiacyl and syringyl nuclei in 72% sulfuric acid

To elucidate the formation and chemical structures of water-soluble material in acid-soluble lignin (ASL), lignin aromatic nuclei model compounds of creosol (I) and 5-methoxycreosol (II) were reacted with xylose or xylan in the presence of apocynol as a counterpart for condensation in 72% sulfuric acid (SA). The reaction of I gave mainly condensation product. However, the condensation reaction of II with apocynol was suppressed because of steric hindrance from the methoxyl group, and II yielded a C-xyloside after refluxing in 3% SA together with condensation products. To obtain information on CHCl₃-soluble material in ASL, model compounds of arylglycerol--aryl ethers with guaiacyl (VIII) and syringyl (X) nuclei were treated by the Klason procedure. VIII gave only insoluble polymerized product, while X gave insoluble polymerized product and CHCl₃-soluble low molecular weight products, which were dissolved in 3% SA. These results prove earlier views that water-soluble material in ASL consists of condensation products formed from syringyl lignin and monosaccharide units in hemicellulose. In addition, the CHCl₃-soluble material in ASL appears to be composed of low molecular weight degradation products from SA treatment of Klason lignin with the syringyl nucleus.Part of this report was presented at the 51st Annual Meeting of the Japan Wood Research Society, Tokyo, April 2001 and at the 47th Lignin Symposium, Fukuoka, October 2002, and was reviewed in Mokuzai Gakkaishi (2002) 48:55–62