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.     

Preparation of acetylated wood meal and polypropylene composites II: mechanical properties and dimensional stability of the composites

Acetylated wood meals of Sugi (Cryptomeria japonica D.Don) wood were prepared by mechanochemical processing using a high-speed vibration rod mill. Weight percent gain (WPG) of the acetylated wood meals ranged from 7.0 to 35.5 %. Wood–plastic composites (WPCs) containing 50 % acetylated woods were produced by an injection molding technique. The polymer matrix used was polypropylene homopolymer. Maleic anhydride-grafted polypropylene (MAPP) was also used as a compatibilizing agent. The mechanical properties of WPCs in bending and tensile tests were independent of WPG of acetylated wood meals, and the test values for WPCs containing acetylated wood meals were lower than that of unmodified wood meal. The use of MAPP increased bending and tensile strength, but no effect on bending modulus was found. An increase in WPG significantly decreased water absorbability and thickness swelling of WPCs as measured by dimensional stability tests. These results demonstrated that mechanochemical processing is a promising technique for preparing WPC material with improved dimensional stability. The future challenge is to inhibit the decreases in mechanical properties of WPCs containing acetylated wood meals.     

Micromorphology,moisture sorption and mechanical properties of a biocomposite based on acetylated wood particles and cellulose ester

Abstract

One of the major issues in a long-term perspective for the use of wood–plastic composites (WPCs) in outdoor applications is the moisture sensitivity of the wood component and the consequent dimensional instability and susceptibility to biological degradation of the composite. In this work, the effects of using an acetylated wood component and a cellulose ester as matrix on the micromorphology, mechanical performance and moisture uptake of injection-moulded WPCs have been studied. Composites based on unmodified and acetylated wood particles, specially designed with a length-to-width ratio of about 5–7, combined with both cellulose acetate propionate (CAP) and polypropylene (PP) matrices were studied. The size and shape of the wood particles were studied before and after the processing using light microscopy, and the micromorphology of the composites was studied using a newly developed surface preparation technique based on ultraviolet laser irradiation combined with low-vacuum scanning electron microscopy (LV-SEM). The water vapour sorption in the composites and the effect of accelerated weathering were measured using thin samples which were allowed to reach equilibrium moisture content (EMC). The length-to-diameter ratio was only slightly decreased for the acetylated particles after compounding and injection moulding, although both the unmodified and the acetylated particles were smaller in size after the processing steps. The tensile strength was about 40% higher for the composite based on acetylated wood than for the composite with unmodified wood using either CAP or PP as matrix, whereas the notched impact strength of the composite based on acetylated wood was about 20% lower than those of the corresponding unmodified composites. The sorption experiments showed that the EMC was 50% lower in the composites with an acetylated wood component than in the composites with an unmodified wood component. The choice of matrix material strongly affected the moisture absorptivity of the WPC. The composites with CAP as matrix gained moisture more rapidly than the composites with PP as matrix. It was also found that accelerated ageing in a Weather-Ometer® significantly increased the moisture sensitivity of the PP-based composites.     

Surface deterioration of wood-flour polypropylene composites by weathering trials

The market for wood-fiber plastic composites (WPCs) is expanding rapidly in many countries including Japan, where WPCs are mainly used for exterior products. In such applications, WPCs undergo undesirable color change, chalking, and shrinkage and swelling, and accordingly there is a need to better understand the mechanisms responsible for the weathering of WPC and develop methods of improving their weathering resistance. In this study, weatherability of WPC was assessed by natural and accelerated weathering trials. Discoloration (whitening) of WPC during exposure was caused by degradation of both wood and plastic. Darker color pigments as additives improved the color stability of WPC; however, chalking on the surfaces still occurred. The color stability of WPC was improved by application of exterior coatings. Preweathering of WPC (before coatings were applied) increased the absorption of coatings by the WPC and had a positive effect on the color stability and prevented chalking of the composites. Parts of this study were presented at the IUFRO XXII World Congress Meeting, Brisbane, August 2005 and the IAWPS 2005, Yokohama, November 2005     

微发泡木塑复合材料耐腐性能的研究

研究了5种不同木塑比的木塑复合材料的天然耐腐性能。结果表明:①木塑复合材料的天然耐腐性能为强耐腐等级,受菌侵染后质量损失率随着木粉含量的提高而增大,但均小于3.5%,方差分析表明,木粉含量对试件质量损失率的影响高度显著,指数函数y=a×exp(x/b)+c对5种木塑材料的平均质量损失率拟合结果较好,决定系数R2为0.923 58;②通过SEM和DSC分析,木塑材料受菌侵染后,主要是木质材料受到了破坏。     

Hygroscopic thickness swelling rate of composites from sawdust and recycled plastics

The thickness swelling rates of compression molded wood plastic composites (WPCs) prepared from 50% by weight sawdust and 50% by weight virgin and/or recycled plastics (HDPE and PP) were studied. Thickness swelling rates of the manufactured WPCs were evaluated by immersing them in water at room temperature and monitoring thickness changes for several weeks. A swelling model developed by Shi and Gardner (Composites Part A, 37:1276–1285, 2006) was used to study the thickness swelling process of WPCs. The parameter K _SR of the model can be used to quantify the swelling rate. The results indicated that composites containing PP had lower equilibrium thickness swelling and also shorter equilibrium time (time to reach equilibrium thickness swelling). The swelling model developed was a good predictor of the hygroscopic swelling process of wood plastic composites. Composites containing PP (virgin and recycled) had higher K _SR than those containing HDPE. The minimum and maximum K _SR values were observed in composites made of virgin HDPE and a mixture of recycled plastics, respectively. With increasing recycled plastic content K _SR linearly decreased.     

热氧老化和水浸渍对木粉/HDPE和稻壳粉/HDPE两种复合材料性能的影响

木粉和稻壳粉是制备木塑复合材料(WPC)常用原料。WPC在使用过程中经常受到热和水分的影响,笔者对比研究了稻壳粉/HDPE和木粉/HDPE两种复合材料经历热氧老化和长时间水浸渍后性能的变化规律。结果表明:木粉/高密度聚乙烯(HDPE)复合材料的弯曲强度和弹性模量都大于稻壳粉/HDPE的;随着热氧老化或水浸渍处理时间的延长,复合材的挠曲性能下降,其中木粉/HDPE复合材的弹性模量下降最为迅速;复合材料表面明度值随着热处理时间的延长而减小,说明颜色变暗,稻壳粉与木粉填充的复合材之间差别不大。通过光学显微镜观察发现,HDPE与稻壳粉或木粉之间都有缝隙存在,为水分和氧气的进出提供了通道。     

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.     

Photodegradation of wood flour/polypropylene composites incorporated with carbon materials with different morphologies

ABSTRACT

In this study, wood flour/polypropylene (WF/PP) composites were prepared by incorporating 2?wt% carbon materials with different morphologies, including carbon black (CB), graphite (G), and multi-walled carbon nanotubes (CNTs). WF/PP composite without any additives was included as a reference. All composites were placed in the accelerated UV weathering tester for a total of 960 h. The physical and mechanical properties of composites were compared. The changes in surface morphology and surface chemistry were characterized by SEM AFM, and ATR-FTIR. The results showed that: (1) the addition of CNTs improved both flexural and impact properties of composites; (2) composites containing CNTs exhibited better color stability and less severe surface cracking during weathering; and (3) ATR-FTIR results revealed that all the additives alleviated surface photo-oxidation of composites due to their UV-screening effect. Overall, due to the improved interfacial bonding between WF and PP, CNTs were more effective in protecting wood–plastic composites from photodegradation.     

Performance of three-layer composites with densified surface layers of Nothofagus pumilio and N. antarctica from Southern Patagonian forests

Nothofagus pumilio and N. antarctica forests of Southern Patagonia, Argentina are currently being managed for production of saw logs with fast growing conditions. The result of these management strategies is faster growing forests, but also an increase in the percentage of low-density wood. The motivation for this study was to find a way to valorise this low-density wood. Surface and bulk densification treatments were applied these wood species and were then applied as face layers in three-layer composites. The mechanical properties of three-layer composites were studied. The modulus of elasticity, modulus of rupture, and modulus of hardness were improved compared to many types of structural composite lumber. This increase in mechanical properties of N. pumilio and N. antarctica wood opens the possibility for its use in structural composites and added value to these otherwise underutilised and undervalued species.     

Cellulose esters as compatibilizers in wood/poly(lactic acid) composite

One of the important issues relevant to wood/plastic composite molding is the compatibility between hydrophilic wood and hydrophobic plastic. Polyolefins modified with maleic anhydride, which have been frequently used for wood and polyolefin composites, are not effective for poly(lactic acid) composites. Because compounds with both hydrophilic and hydrophobic groups are potential compatibilizers, cellulose esters of several carboxylic acids, RCOO-cellulose (R = CH₃, C₂H₅, C₃H₇, C₄H₉, C₅H₁₁, C₁₁H₂₃), were synthesized and their effects as compatibilizers of wood/poly(lactic acid) composites (WPLC) were examined in this study. The mechanical properties of WPLC were improved with a small amount of added cellulose esters, especially cellulose butyrate or cellulose valerate. The relevant effect of added cellulose esters on the thermal properties of wood/PLA composite was analyzed by measuring dynamic viscoelasticity. Part of this report was presented at the 56th Annual Meeting of Japan Wood Research Society, Akita, August 2006 and the 9th International Conference on Frontiers of Polymers and Advanced Materials, Cracow, Poland, July, 2007     

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。     

Properties of flat-pressed wood plastic composites as a function of particle size and mixing ratio

This paper presents the effects of particle size and mixing ratio on the properties including physical, mechanical, and decay resistance of wood plastic composites (WPCs). In addition, it also presents the effects of immersion temperatures on water absorption (WA) and thickness swelling (TS) of the WPCs. WPCs with a thickness of 6 mm were fabricated from Albizia richardiana King & Prain wood particles and recycled polyethylene terephthalate (PET) by the flat-press method. To prepare the WPCs, two different wood particle sizes (0.5–1.0 and 1.01–2.0 mm) were used along with four different mixing ratios (w/w). Subsequently, the physical properties include density, moisture content, WA, and TS, and mechanical properties include modulus of elasticity (MOE) and modulus of rupture (MOR) of the produced WPCs was evaluated. Furthermore, decay resistance was evaluated by the weight loss percentage method. Moreover, the effects of immersion temperatures on WA and TS of WPCs after 24 h of immersion in water at three different temperatures, i.e., 25, 50, and 75 °C were investigated. Results showed that the wood particle size had impact on WPC’s density (only 6% decreased with the increase of particle size); however, the density decreased by 29% when the wood particle content increased from 40 to 70%. The WA and TS gradually increased with the increase of particle content and decrease of particle size. In addition, WA and TS increased proportionately with increasing immersion temperature from 25 to 75 °C. Furthermore, the highest MOE (2570 N/mm²) was found for the WPCs fabricated from large wood particles having the ration of 50:50 (wood particle:PET). For decay resistance, WPCs consisted of larger particles and higher PET content showed greater resistance against decay. Therefore, it is comprehensible that fabrication of the WPCs from 50% large particles and 50% PET is technically feasible and further improvement of WPC performance like enhancement of MOE and reduction of density using coupling agent and agricultural waste fibers, respectively, in the WPC formulation is recommended.     

植物纤维/塑料复合材作地板基材的研究

Three kinds of composites （fiber/Polypropylene, fiber/Polyethelene, and fiber/Polystyrene） were made by using hot pressing process for substrate of floorboard and the properties of each kind of composites were tested. MORs of PP/wood fiber, PS/fiber, and PE/fiber composites with coupling agent added were raised by 18.4%, 37.1%, and 42%. respectively, compared to those without coupling agent. Among the three kinds of fiber/plastic composites, fiber/PP composite has best mechanical properties, and it can meet quality standard of eligible grade product and come up to the excellent grade products of China when the coupling agent is added. The performance of composite made of PE/fiber or PS/fiber can exceed qualified product grade only with coupling agent added.     

光老化时间对旱柳枝桠材纤维/聚乳酸复合材料性能的影响

采用自然光对比不同纤维含量木纤维/聚乳酸复合材料进行光照老化试验,对比经过不同时间光照后材料的弯曲性能以及拉伸性能的变化,分析光照时间对材料力学性能的影响。结果显示,加入木纤维后,复合材料的弯曲强度和拉伸强度均出现了先下降后上升的趋势,说明加入一定量的木纤维会对复合材料体系起到一定的增强作用;在受到一定时间的自然光照射后,纯聚乳酸材料和木纤维/聚乳酸材料的弯曲性能和拉伸性能均有显著降低,含有木纤维的复合材料强度降低较少。     

亚麻屑/高密度聚乙烯复合材料性能研究

采用两步法工艺和设备,按照9组实验配方,在基础配方的基础上,添加铁红和UV531作为添加剂,制备出亚麻屑/高密度聚乙烯复合材料。分析了加入不同添加剂的复合材料老化前后的弯曲性能、冲击性能和密度。实验数据表明,亚麻屑含量为60%、添加抗老化剂UV531的木塑复合材料物理及力学性能较好,得出了加工亚麻屑/HDPE复合材料的最优工艺和实验配方。     

Using master curves based on time–temperature superposition principle to predict creep strains of wood–plastic composites

To verify master curves obtained based on time–temperature superposition principle for wood–plastic composites (WPCs), a 220-day long-term creep test was conducted under an unconditioned environment. In this study, WPCs were made by extrusion with various formulations; using mountain pine beetle-attacked lodgepole pine flour and high-density polyethylene as raw materials, as well as maleated polypropylene as coupling agent. The results showed that the effect of naturally elevated temperature during the summer months caused additional increases in creep strain. The information obtained from the conventional creep study method may be insufficient to reflect the practical application. Comparisons between long-term data and the master curves showed that the master curves tended to overestimate the real creep strain of large specimens and that the deviation increased with time. The prediction of the master curve agreed more reasonably with the long-term data for coupled WPC products, whereas the master curves showed considerable overestimation for the uncoupled ones. In general, the master curves cannot precisely predict the long-term creep strain, but merely provide conservative estimations.     

Formation of carbon–carbon composite using wood as a precursor

Abstract

The use of wood as structure-giving material may be an effective approach to reduce some barriers for producing high temperature ceramic especially carbon composites. The objective of this study was to develop a simple process for producing carbon–carbon (C–C) composite through porous template result from pyrolysing of wood. Walnut, known to be relatively permeable, was being heat treated under controlled atmosphere. The carbon-template formed was infiltrated with coal tar pitch. Morphological characterization of the resulting composite was carried out by scanning electron microscopy morphology and physical properties of sample were evaluated with determination of bulk density and open porosity. In addition mechanical properties of products were analysed with three-point bending test and Vickers micro hardness. Results showed that bulk density had an uprising trend with increasing the number of densification cycles and subsequently open porosity decreased. Moreover, from mechanical property's point of view, results had a good compatibility with increase in the densification cycles.     

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]     

聚丙烯/亚麻纤维复合材料的性能研究

研究了亚麻纤维(flaxfiber,FF)的含量和马来酸酐接枝聚丙烯(MAH-g-PP)对聚丙烯/亚麻纤维(PP/FF)复合材料各项性能的影响,通过扫描电镜研究了复合材料的界面结构.结果表明:随着FF含量增大,复合材料拉伸强度、硬度和热变形温度提高;添加MAH-g-PP提高了复合材料力学性能和热稳定性,降低了复合材料吸水性.