Performance of thermomechanical wood fibers in polypropylene composites

ABSTRACT

Thermomechanical wood fibers, as usually used for medium density fiberboard or cardboard production, feature promising characteristics, like a high aspect ratio, for the utilization in thermoplastic composites. The present study investigates the influence of fiber loading and fiber geometry on the mechanical properties of wood-polypropylene composites in order to confirm the results that were found in a previously published literature review. Composites were compounded at fiber contents from 20 to 60 wt.%, using a co-rotating twin-screw extruder and subsequently injection molded to test specimens. Field emission scanning electron microscopy was carried out to evaluate the fracture morphology of the composites. Fiber length was evaluated using an applying a dynamic image analysis system. Compounding reduced fiber lengths up to 97%. The mechanical properties decreased with increasing fiber content for composites without a coupling agent. Strength properties peaking at a fiber content of 50?wt.% for composites containing MAPP. Tensile strength and flexural strength reached 48.1 and 76.4 MPa, respectively. However, it was found that the processing of these fibers into conventional compounding equipment is still challenging.     

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.     

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 polypropylene, but the tensile and unnotched charpy impact strength decreased. And the above strength decreased with the wood fiber content increasing. When the wood fiber size becoming smaller (in higher mesh), the strength increased. In the comparison of wood species, the properties of composite using Chinese fir wood were better than that of Poplar, but not significant. The dynamic mechanical properties of the composites and PP were also tested and analyzed in this paper.     

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.     

Fundamental studies on wood/cellulose-plastic composites: effects of composition and cellulose dimension on the properties of cellulose/PP composite

Although wood/cellulose-plastic composites (WPC) of low wood/cellulose content have been more accepted worldwide and are promoted as low-maintenance, high-durability building products, composites containing high wood/cellulose content are not yet developed on an industrial scale. In this study, flow properties, mechanical properties, and water absorption properties of the compounds of cellulose microfiber/polypropylene (PP) and maleic anhydride-grafted polypropylene (MAPP) were investigated to understand effects of the high cellulose content and the dimensions of the cellulose microfiber. The molding processes studied included compression, injection, and extrusion. It was found that fluidity is not only dependent on resin content but also on the dimension of the filler; fluidity of the compound declined with increased fiber length with the same resin content. Dispersion of the composite was monitored by charge-coupled device (CCD) microscope. Increasing the plastic content in the cellulose-plastic formulation improved the strength of mold in addition to the bond development between resin and filler, and the tangle of fibers. The processing mode affected the physicomechanical properties of the cellulosic plastic. Compression-molded samples exhibited the lowest modulus of rupture (MOR) and modulus of elasticity (MOE) and the highest water absorption, while samples that were injection-molded exhibited the highest MOR (70 MPa) and MOE (7 GPa) and low water absorption (2%).     

Improved interaction between wood and synthetic polymers in wood/polymer composites

Summary This article describes the properties of wood polymer composites consisting of linear low density polyethylene (LLDPE) and wood flour (WF). In an attempt to improve the interfacial adhesion between the matrix and the filler, different compatibilizers were used. The interaction between polymer and wood were studied by comparing LLDPE/WF composites with composites when compatibilizer was added. The experimental measurements were conducted by impact and tensile strength testing and Scanning Electron Microscopy (SEM). The mechanical properties of the composites were improved with SEBS triblock copolymer modified with maleic anhydride and with the ionomer polymer, Surlyn, as compatibilizers. SEM fractography confirmed better adhesion between wood particles and LLDPE matrix when SEBS was present.This study was financed by the Swedish National Board for Industrial and Technical Development (NUTEK) which is gratefully acknowledged     

Field test of resistance of modified wood to marine borers

Abstract

Five mineral fillers were tested for wood–plastic composites (WPCs): calcium carbonate, two different types of wollastonite, soapstone and talc. The impact of the fillers on the mechanical properties of the composites was studied. The experiments included bending tests, tensile tests, Brinell hardness and scanning electron microscopy experiments. The amount of wood, mineral and plastic (polypropylene) was kept steady. Only the mineral type was changed during the tests. A control sample without any mineral added was also manufactured. The mineral addition improved the tensile strength of the WPCs. The hardness of the composite was also improved when the minerals were added, and along with the increasing mineral hardness, the hardness of the composite increased. The wollastonite acicular shape was crushed during the manufacturing process, so the phase of the process in which the minerals are added requires careful consideration.     

金属纤维与木单板的复合

为了赋予木基复合材料电磁屏蔽功能,在脲醛树脂胶中加入黄铜纤维和不锈钢纤维作为导电单元,制备三层结构的落叶松复合胶合板,研究金属纤维不同施加量以及涂胶量对木基复合材料电磁屏蔽性能(SE)和胶合强度(ST)的影响.结果表明,除SF25-80外,胶合强度均达到或超过国家标准,涂胶量增大对电磁屏蔽效能有不利影响.在施加黄铜纤维条件下,电磁屏蔽效能为6.34～28.76dB,电磁屏蔽和胶合强度模型均不显著;在施加不锈钢纤维条件下,胶合板的电磁屏蔽效能为13.63～21.14dB,电磁屏蔽模型显著,胶合强度模型不显著.金属纤维的加入一方面有利于导电网链的形成,但另一方面对胶合强度有不利影响,进而不利于胶合板的导电性,电磁屏蔽性能是这两个方面综合作用的结果.     

Nanoindentation of juvenile and mature loblolly pine (<Emphasis Type="Italic">Pinus taeda</Emphasis> L.) wood fibers as affected by thermomechanical refining pressure

The effects of thermomechanical refining pressures, varying from 2 to 18 bars, on the cell-wall properties of refined wood fibers of a 54-year-old loblolly pine (Pinus taeda L.) with reference to both juvenile (JW) and mature wood (MW) were investigated using nanoindentation and atomic force microscopy. The results of this study indicate that refining pressure plays a significant role in the physical damage sustained by refined wood fibers. No obvious damage was observed in the cell walls of MW fibers refined at 2 and 4 bar. Nanocracks (<500 nm in width) were found in fibers refined at pressures in the range of 2–12 bar for JW and 6–12 bar for MW, and micro cracks (>3,000 nm in width) were found in both MW and JW fibers subjected to a refining pressure of 14 and 18 bar. The micro damage to the fibers refined at higher pressures was more severe inside the lumen than on the surface of the fibers, and the lumen or S₃ layer was significantly damaged. The elastic modulus, hardness, and creep resistance of MW fibers were higher than those of the JW fibers subjected to the same refining-pressure conditions. The elastic modulus and hardness decreased, whereas nanoindentation creep increased, with increasing refining pressure. This study also suggests that lower refining pressures (<4 bar) and higher pressures (>14 bar for MW and >12 bar for JW) should be avoided in the manufacture of fiberboards and wood fiber–polymer composites, because of the lower aspect ratio of the fiber bundles, shorter length of the fibers and fines, and severe damages to the fiber cell walls.     

Crash simulation of wood and composite wood for future automotive engineering

ABSTRACT

Multi material mix is a promising approach to reduce weight and the carbon footprint in automotive engineering at competitive costs. As a result, automotive industry is getting more venturous, exploring and applying other materials than metals and plastics – e.g. fibre reinforced plastics (FRPs). In this context, engineered wood products (EWPs) and wood composites should be considered: Wood composites provide high stiffness, strength, excellent damping, high resistance against fatigue and a very low density at low material costs. It is hypothesized that modern wood composites are competitive to metals and artificial fibre-reinforced materials when designed and applied properly. The application of wood and wood composites in automotive engineering calls for precise and reliable material data, required for initial material selection and later in numerical simulation. In this study, a material model normally used for modelling FRPs was adopted. A material database was generated for three hardwood species, to establish the required material parameters and validate material model. Results prove that wooden components can be simulated in crash situations and the selected material model is applicable, even in full vehicle simulation.     

改性剂对木塑复合材料力学性能影响的研究

采用木材纤维,分别与PE、PS、ABS、SAN等热塑性高分子聚合物,经热压复合工艺制成木塑复合板材,通过加入不同的改性剂以及改变改性剂的加入量,研究它们对木塑复合材料力学性能的影响。结果表明:改性剂的加入能使木材纤维与各种热塑性高分子聚合物很好地胶接;改性剂不同对木塑复合材料的性能产生不同的影响;改性剂的加入量为木材纤维用量的5%时,该法制作的木塑复合板材力学性能最佳。     

A method to determine lumen volume and collapse degree of pulp fibers by using bottleneck effect of mercury porosimetry

On applying mercury porosimetry to wood blocks or paper sheets, the “bottleneck” effect due to pits of fibers occurs and thus lumen volume can be determined from the weight increase due to the remaining mercury. However, in addition to the mercury in the lumen, some mercury drops may also remain in the space between fibers within a paper sheet. The mercury between fibers increased with an increase of basis weight. Thus, a large number of paper sheets of low basis weight, such as 10 g·m⁻², should be used to determine the lumen volume of pulp fibers. Furthermore, in the case of fibers from mechanical pulp with many open cut fibers, mercury can retract from the open lumen such that the bottleneck effect due to pits does not occur. Therefore, the degree to which fibers are cut should also be considered for lumen volume determination. Although quantitative estimation of open cut fibers is difficult, the percentage of open cut fibers is quite low for the long fiber fraction. Thus, the remaining mercury for the long fiber fraction can be adopted as the lumen volume at least for practical purposes. Compared with the original lumen volume of the wood, the volumetric degree of fiber collapse was also estimated. Plausible values of almost 100% for lightly beaten KP and about 85% for slabwood thermomechanical pulp were obtained for the degree of collapse. Part of this report was presented at the 56th Annual Meeting of the Japan Wood Research Society, Akita, August 2006     

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.     

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。     

木纤维素与合成聚合物复合材料的研究进展

作为合聚俣物复合材料增强的木纤维素包括木纤维素粉和纤维素纤维。本文综述３个方面主要的研究进展；木纤维素粉在热固性塑料中的增强，用偶俣剂涂覆纤维素纤维在热塑性聚合物中的增强以及纤维素纤维在易生物降解聚俣物的增强。简要介绍了三类木纤维素增强复合材料的性质，指出最终的目标是制备符合环保要求完全物降解的复合材料。     

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.     

Lignin characteristics of bast fiber and core in kenaf, bark and wood of paper mulberry and mulberry

The structural features of bast fiber and core lignins in kenaf (Hibiscus cannabinus), bark and wood lignin of paper mulberry (Broussonetia papyrifera (L.) Vent × Broussonetia kazinoki Sieb.) and mulberry (Morus bombycis) were characterized by alkaline nitrobenzene oxidation, ozonation and methoxyl group determination. Bj?rkman lignins were isolated from bast fiber and core, and bark and wood fractions of the plant samples, and structural characteristics were investigated by ¹H NMR and ¹³C NMR spectroscopies. Kenaf bast fiber gave very high molar ratio of syringaldehyde to vanillin (S/V) of alkaline nitrobenzene oxidation products, while methoxyl content was about the same as that of the core fraction. Results of ¹H NMR and ¹³C NMR of Bj?rkman lignin suggested the presence of aliphatic fragments in lignins isolated from paper mulberry and mulberry bark, but not in kenaf bast fiber. The lower yield of alkaline nitrobenzene oxidation products from bast fiber and bark might be due to the higher content of condensed structure of lignin compared to core fraction. Total yield of erythronic (E) and threonic (T) acids of ozonation products and the molar ratio of erythronic acid to threonic acid (E/T) of the bast fibers and bark were lower than the corresponding core and wood fractions, suggesting that the contents of arylglycerol-β-aryl ether intermonomer linkages in the bast fiber and bark lignin were lower than those of the core and wood fractions. Methoxyl content of bark lignin was lower than the corresponding wood lignin. The methoxyl content of the extract-free kenaf bast fiber was similar to that of the core fraction, while the values of paper mulberry and mulberry bark were about one-half of the corresponding wood fractions, respectively. In bark lignins, the methoxyl contents of Klason lignin and Bj?rkman lignin from bark were lower than those of the extract-free barks. This result suggests that the purity of Klason lignin and Bj?rkman lignins of bark may be rather low.     

Recent research and development work on wood composites in Japan

Summary This paper highlights a number of articles on research and development on wood composites. The coefficient of variation in the mechanical properties of wood components tends to decrease when the thickness of the wood elements decreases. This finding was utilized in the manufacture of hollow cylindrical columns of laminated veneer lumber (LVL) from Cryptomeria plantation thinnings. In the future, the marketing of wood composite boards will tend toward two types: thick boards with low density properties and thin boards with fiber orientation. For the production of thick boards, fundamental parameters and application of steam-injection pressing have been studied, and continuous steam-injection pressing has been developed. For thin board production, generation principles of aligning torque in high-voltage system and the application has been studied. A new oriented mat former with electrodes positioned only at the reverse side of a forming belt has been developed. Various synthetic resins of low-molecular weight have been applied to improve dimensional stability of laminated products, such as LVLs and particleboards. Acetylation and formalyzation of fibers and particles were investigated to provide stabilized panels. High pressure steam treatment during pressing of wood composites has been studied and the process has been found effective and promising.The authors wish to thank Mr. Dwight A. Eusebio for his help in the preparation of this paperThis paper was presented at the IUFRO All Division 5 conference in Nancy, France, on August 15, 1992     

Effect of impact velocity on the fracture of wood as related to the mechanical pulping process

 The fiber separation step in refining is crucial for energy consumption in subsequent refining where the pulp properties are developed. The size reduction of chips during refining is dependent on refining intensity and chip strength. Factors affecting these two parameters are discussed in a literature review. The impact strength of chips and the break down of chips to separate fibers are also discussed. Specifically the effect of impact velocity on the fracture of wood has been studied by use of a falling weight impact tester. Samples were prepared from a freshly cut log of Norway spruce, Picea abies, and the impact strength was measured using an instrumented falling weight impact tester. An increase in impact velocity from about 2.7 to 4.8 m/s resulted in an increase in impact strength of about 50%. Received 23 August 1999     

Investigation on the compatibilizing effect of m-isopropenyl-α,α-dimethylbenzyl isocyanate grafted polypropylene on polypropylene and wood flour composites

Wood flour (WF) and polypropylene (PP) composites (WF/PP) were compatibilized by m-isopropenyl-α,α-dimethylbenzyl isocyanate grafted polypropylene (m-TMI-g-PP). The effect of wood flour, m-TMI-g-PP contents on the rheology, dynamic mechanical analysis (DMA), mechanical properties, as well as the morphology of the composites were investigated and discussed. Rheology, DMA results showed that m-TMI-g-PP was an effective compatibilizer for WF/PP composites. The shear modulus (G′) and complex viscosity (η*) of the composites were increased, which implied that the composites probably withstood pronounced shear forces, resulting from strong adhesion at the interface between the matrix PP and WF. The mechanical test indicated that the tensile strength and the flexural strength of the composites were improved with increasing content of m-TMI-g-PP. From the properties tests, the optimum loading of WF in WF/m-TMI-g-PP/PP was found to be 40%, and the optimum loading of m-TMI-g-PP was 6%. Property enhancement is attributed to improved wetting and interactions between the PP matrix and WF, which is supported by scanning electron microscopy analysis.