Moisture uptake and hygroexpansion of wood fiber composite materials with polylactide and polypropylene matrix materials

Effects of butantetracarboxylic acid (BTCA) modification, choice of matrix, and fiber volume fraction on hygroexpansion of wood fiber composites have been investigated. Untreated reference wood fibers and BTCA‐modified fibers were used as reinforcement in composites with matrices composed of polylactic acid (PLA), polypropylene (PP), or a mixture thereof. The crosslinking BTCA modification reduced the out‐of‐plane hygroexpansion of PLA and PLA/PP composites, under water‐immersed and humid conditions, whereas the swelling increased when PP was used as matrix material. This is explained by difficulties for the BTCA‐modified fibers to adhere to the PP matrix. Fiber volume fraction was the most important parameter as regards out‐of‐plane hygroexpansion, with a high‐fiber fraction leading to large hygroexpansion. Fiber‐matrix wettability during processing and consolidation also showed to have a large impact on the dimensional stability and moisture uptake. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Moisture uptake and resulting mechanical response of bio‐based composites. II. composites

The durability of entirely bio‐based composites with respect to the exposure to elevated humidity was evaluated. Different combinations of bio‐based resins (Tribest, EpoBioX, Envirez) and cellulosic fibers (flax and regenerated cellulose fiber rovings and fabrics) were used to manufacture unidirectional and cross‐ply composite laminates. Water absorption experiments were performed at various humidity levels (41%, 70%, and 98%) to measure apparent diffusion coefficient and moisture content at saturation. Effect of chemical treatment (alkali and silane) of fibers as protection against moisture was also studied. However, fiber treatment did not show any significant improvement and in some cases the performance of the composites with treated fibers was lower than those with untreated reinforcement. The comparison of results for neat resins and composites showed that moisture uptake in the studied composites is primarily due to cellulosic reinforcement. Tensile properties of composites as received (RH = 24%) and conditioned (RH = 41%, 70%, and 98%) were measured in order to estimate the influence of humidity on behavior of these materials. Results were compared with data for glass fiber reinforced composite, as a reference material. Previous results from study of unreinforced polymers showed that resins were resistant to moisture uptake. Knowing that moisture sorption is primarily dominated by natural fibers, the results showed that some of the composites with bio‐based resins performed very well and have comparable properties with composites of synthetic epoxy, even at elevated humidity. POLYM. COMPOS., 36:1510–1519, 2015. © 2014 Society of Plastics Engineers     

Moisture absorption properties of wood‐fiber‐reinforced recycled polypropylene matrix composites

To reduce the moisture absorption of wood‐fiber‐reinforced recycled plastic composites (WRPCs), a coupling agent (KH550), methyl methacrylate (MMA), and maleic anhydride (MA) were used to modify the wood fibers. The surface‐treated wood fibers were mixed with recycled polypropylene and processing agents to fabricate the WRPCs. The mechanical properties and moisture absorption behavior of the WRPCs were determined. The results showed that the three surface treatment methods could effectively reduce the moisture absorption and thickness swelling of WRPCs. In Comparison to the properties of untreated wood‐fiber‐reinforced WRPCs, the moisture absorption ratio of WRPCs with wood fibers treated by MMA, KH550, and MA was reduced by 31.4%, 49.8%, and 38.2%, respectively, and the tensile strength was increased by 22.1%, 26.3%, and 4.2%, respectively. The impact toughness of the WRPCs was increased by 36.2% KH550 treatment and 19.2% for MMA treatment but was decreased by 4.2% for MA treatment. Coupling treatment of the wood fibers was the best way to reduce the moisture absorption of WRPCs, and this kind of WRPC possessed the best comprehensive properties. J. VINYL ADDIT. TECHNOL., 2010. © 2009 Society of Plastics Engineers     

Effects of alkaline and silane treatments on the water‐resistance properties of wood‐fiber‐reinforced recycled plastic composites

The water‐resistance properties of wood‐fiber‐reinforced recycled plastic composites (WRPCs) prepared from postconsumer high‐density polyethylene (HDPE) and wood fibers from saw mills were studied. Three methods consisting of an alkaline method (AM), a silane method (SM), and a combination of the alkaline and silane methods (ASM) were used to modify the wood fibers. The effects of fiber/matrix mix ratio and surface treatment on the moisture content, thickness swelling, and flexural strength change of the WRPCs, before and after immersion in 60°C water for 8 weeks, were studied and analyzed. The flexural fractured surfaces of the WRPCs before and after immersion in hot water were examined, and the fracture mechanism of the WRPCs was discussed. The results showed that the different surface treatments of the wood fibers had significant effects on the moisture content, thickness swelling, and flexural strength of the WRPCs after a long immersion time in hot water. For WRPCs treated by ASM, the moisture content was the lowest, the thickness swelling was at a minimum, and the flexural strength was the highest. Higher water absorption of composites with fiber treated by the AM or SM methods, as compared to those treated by ASM, could be attributed to the incomplete adhesion and wettability between the wood fibers and the polymer matrix, which may have caused more gaps and flaws at the interface. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.     

Effect of moisture content on mechanical properties,thermal and structural stability and extrudate texture of poly(vinyl chloride)/wood sawdust composites

Mechanical properties and thermal and structural changes of poly(vinyl chloride) (PVC)/wood sawdust composites were assessed with respect to the effect of moisture content, varying from 0.33 to 3.00 % by weight in the composite, for three different wood sawdust contents. The swell ratio and texture characteristics of the composite extrudates were also evaluated. Unique explanations were given to describe changes in the composite properties in terms of molecular interactions between PVC, cellulosic sawdust and moisture, such as dipole–dipole interactions, interfacial defects and bonding, fibre swelling, and moisture evaporation. The results suggest that at low moisture content the tensile modulus decreased and elongation at break of the composites increased with moisture content, the effect being reversed for high moisture content. Tensile strength decreased with increasing moisture content up to 1–2 %, and then unexpectedly increased at higher moisture contents. The effect of moisture content on flexural properties of the composite was similar to that on tensile properties. Impact strength of the composites was considerably improved with moisture content at low sawdust contents (16.7 wt%), and was independent of the moisture content at higher sawdust contents (28.6 and 37.5 wt%). A decrease in decomposition temperature with an increase in polyene content was evidenced with increasing moisture content, while the glass transition temperature did not change with varying moisture content. The extrudate swell ratio increased with the shear rate but remained unaffected by moisture content. The bubbling and peeling‐off in the composite extrudate occurred as a result of the evaporation of water molecules and the application of a high shear rate. Copyright © 2004 Society of Chemical Industry     

Foaming of PS/wood fiber composites using moisture as a blowing agent

This paper presents an experimental study on foam processing of polystyrene (PS) and high‐impact polystyrene HIPS/wood‐fiber composites in extrusion using moisture as a blowing agent. Wood‐fiber inherently contains moisture that can potentially be used as a blowing agent. Undried wood‐fiber was processed together with PS and HIPS materials in extrusion and wood‐fiber composite foams were produced. The cellular morphology and volume expansion ratios of the foamed composites were characterized. Because of the high stiffness of styrenic materials, moisture condensation during cooling after expansion at high temperature did not cause much contraction of the foamed composite and a high volume expansion ratio up to 20 was successfully obtained. The experimental results showed that the expansion ratio could be controlled by varying the processing temperature and the moisture content in the wood fiber. The effects of a small amount of a chemical blowing agent and mineral oil on the cell morphologies of plastic/wood‐fiber composite foams were also investigated.     

Manufacture of rigid PVC/wood‐flour composite foams using moisture contained in wood as foaming agent

Relatioships between the density of foamed rigid PVC/wood‐flour composites and the moisture content of the wood flour, the chemical foaming agent (CFA) content, the content of all‐acrylic foam modifier, and the extruder die temperature were determined by using a response surface model based on a four‐factor central composite design. The experimental results indicated that there is no synergistic effect between teh CFA content and the moisture content of the wood flour. Wood flour moisture could be used effectively as foaming agent in the production of rigid PVC/wood‐flour composite foams. Foam density as low as 0.4 g/cm³ was produced without the use of chemical foaming agents. However, successful foaming of rigid PVC/wood‐flour composite with moisture contained in wood flour strongly depends upon the presence of all‐acrylic foam modifier in the formulation and the extrusion die temperature. The lowest densities were achieved when the all‐acrylic foam modifier concentration was between 7 phr and 10 phr and extruder die temperature was as low as 170°C.     

Long‐term water uptake behavior of lignocellulosic‐high density polyethylene composites

Composites of different lignocellulosic materials and high‐density polyethylene were prepared and their long‐term water absorption behaviors were studied. Wood flour, rice hulls, newsprint fibers, and kenaf fibers were mixed with the polymer at 25 and 50 wt % fiber contents and 1 and 2% compatibilizer, respectively. Water absorption tests were carried out on injection‐molded specimens at room temperature for five weeks. Results indicated a significant difference among different natural fibers with kenaf fibers and newsprint fibers exhibiting the highest and wood flour and rice hulls the lowest water absorption values, respectively. Very little difference was observed between kenaf fiber and newsprint composites and between rice hulls and wood flour composites regarding their water uptake behavior. The difference between 25 and 50% fiber contents for all composite formulations increased at longer immersion times, especially for the composites with higher water absorption. Kenaf fiber composites containing 50% kenaf fibers exhibited the highest water diffusion coefficient. A strong correlation was found between the water absorption and holocellulose content of the composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3907–3911, 2006     

Aramid‐short‐fiber reinforced rubber as a tire tread composite

Mechanical and dynamic‐mechanical properties of a typical tire tread compound reinforced with one part aramid short fibers were investigated in order to predict the effects of fibers on tire tread performances such as rolling resistance and traction. Rubber processing, including mixing and extrusion, was performed in an industrial scale. Fiber orientation as a result of extrusion was evaluated quantitatively and qualitatively using mechanical anisotropy in swelling and scanning electron microscopy, respectively. Unidirectional tensile tests revealed higher modulus, but slightly lower strength and elongation at break for the composites stretched in the longitudinal (orientation) and transverse directions than those for the isotropic reference compound with no fiber. Dynamic mechanical thermal analysis showed that relative values of loss factor for the longitudinal and transverse composites and the reference compound depended on the state of polymer as glassy or rubbery. Therefore, a high loss factor at lower temperatures and a low loss factor at higher temperatures predicted a balanced improvement of tire traction and rolling resistance as a result of fiber addition. Heat build‐up and abrasion experiments showed that addition of fiber did not deteriorate other performances of tire tread. Also, the fibers had negligible effects on processing and vulcanization characteristics of the composite. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A novel mica‐based composite with hybrid aramid fibers for electrical insulating applications: largely improved mechanical properties and moisture resistance

The fabrication of mica‐based composites with good mechanical properties is very important especially for electrical insulation applications. In this study, a new aramid fibrid along with chopped fibers was introduced into a mica system, and the composites were prepared using a papermaking machine. It was found that the mechanical properties of both fibrid–mica composite (F‐M paper) and fiber/fibrid–mica composite (A‐M paper) were largely improved in comparison with the reference sample (M paper) with an increase in the content of fibrid or hybrid floc/fibrid. This enhancement can be attributed to two mechanisms: (1) enhanced interfacial adhesion derived from the addition of fibrids with good flexibility and wrapping properties and (2) significant reinforcing due to the frameworks originating from the addition of chopped flocs with high modulus and rigid‐rod morphology. Interestingly, a synergetic effect of enhanced interfacial adhesion and reinforcing could also be observed when both flocs and fibrids were introduced, which further improved the mechanical properties. Furthermore, the addition of aramid fibrid greatly enhanced the moisture resistance, which expands the potential for mica‐based composites. Thus, we successfully fabricated a mica‐based composite for electrical insulation with good mechanical properties, high end‐use temperature and excellent moisture resistance by adding hybrid aramid fibers. © 2017 Society of Chemical Industry     

Durability of Wood Flour-Thermoplastic Composites under Extreme Environmental Conditions and Fungal Exposure

Abstract

The main purpose of this research work was to investigate the response of wood flour reinforced polyethylene composites to 2 hours water boiling, five complete boiling and freezing cycles and fungal (Gloeophyllumm Traebum/Brown-rot fungus) exposure. Five composite formulations were manufactured and analyzed (0, 50, 60, 70 and copper carbonate treated 60% wood flour/polyethylene composites). The results showed that wood flour loading decreased the resistance of the composites to moisture and fungal environment. The exposure of the composites to 2 hours water boiling and five complete boiling and freezing cycles caused serious damage to the interfacial adhesion between wood flour and polyethylene matrix due to contraction and swelling stresses developed during cyclic exposure. The addition of 1 percent copper carbonate salt during compounding of wood flour and polyethylene prevented the colonization and proliferation of fungus on the surface of the composites, but had a negative effect on the water uptake and flexural properties of the composites.     

Wood‐fiber‐reinforced poly(lactic acid) composites: Evaluation of the physicomechanical and morphological properties

This article presents the results of a study of the processing and physicomechanical properties of environmentally friendly wood‐fiber‐reinforced poly(lactic acid) composites that were produced with a microcompounding molding system. Wood‐fiber‐reinforced polypropylene composites were also processed under similar conditions and were compared to wood‐fiber‐reinforced poly(lactic acid) composites. The mechanical, thermomechanical, and morphological properties of these composites were studied. In terms of the mechanical properties, the wood‐fiber‐reinforced poly(lactic acid) composites were comparable to conventional polypropylene‐based thermoplastic composites. The mechanical properties of the wood‐fiber‐reinforced poly(lactic acid) composites were significantly higher than those of the virgin resin. The flexural modulus (8.9 GPa) of the wood‐fiber‐reinforced poly(lactic acid) composite (30 wt % fiber) was comparable to that of traditional (i.e., wood‐fiber‐reinforced polypropylene) composites (3.4 GPa). The incorporation of the wood fibers into poly(lactic acid) resulted in a considerable increase in the storage modulus (stiffness) of the resin. The addition of the maleated polypropylene coupling agent improved the mechanical properties of the composites. Microstructure studies using scanning electron microscopy indicated significant interfacial bonding between the matrix and the wood fibers. The specific performance evidenced by the wood‐fiber‐reinforced poly(lactic acid) composites may hint at potential applications in, for example, the automotive and packaging industries. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4856–4869, 2006     

Influence of mineral fillers on the fire retardant properties of wood‐polypropylene composites

The effects of mineral fillers on the fire retardancy of wood‐polypropylene composites have been studied. Wood‐polypropylene composites containing mineral fillers have been compounded in a conical twin‐screw extruder. A composite manufactured without any mineral filler addition has been used as a reference. The flame resistance properties of the composite materials have been studied using the cone calorimeter. The results show that the introduction of mineral fillers into the wood‐polypropylene composites has a favourable effect on the fire resistance properties of the composite materials. The reaction‐to‐fire properties have been improved according to the fire classification of construction products based on the Euroclass system. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanical performance and moisture absorption of various natural fiber reinforced thermoplastic composites

Natural fibers are seeing increased use in composite applications due to their reduced cost, low density, and environmental benefits (more sustainable and lower carbon footprint). Although many natural fiber systems have been examined over the last decade, there have been relatively few studies which have compared a variety of fiber types and processing methods directly in the same experimental set. In this study, natural fiber composites made from low density polyethylene (LDPE) and a variety of Canadian based fiber feedstocks were examined including hemp bast, flax bast, chemically pulped wood, wood chips, wheat straw, and mechanically pulped triticale. The effect of fiber type, fiber fraction and maleic anhydride polyethylene (MAPE) coupling agent on the mechanical properties and long‐term moisture absorption behavior was quantified. In general, addition of natural fiber to LDPE results in an increase in modulus (stiffness) with a corresponding loss of material elongation and impact toughness. Of the fiber types tested, composites made from chemically pulped wood had the best mechanical properties and the least moisture absorption. However, the use of MAPE coupling agent was found to significantly increase the mechanical performance and reduce moisture absorption for all other natural fiber types. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 969‐980, 2013     

The influence of carbon‐based fillers on the flammability of polypropylene‐based co‐extruded wood‐plastic composite

Comparative analysis of the effect of carbon‐based fillers with different particle sizes and morphologies on the flammable properties of a co‐extruded wood‐plastic composite is performed. Five carbon‐based fillers, namely carbon black, carbon nanotubes, graphite, expandable graphite, and carbon fibers were loaded into the shell layer of the composite. The flammability was characterized by using the cone calorimeter technique. The nanosized fillers, carbon black and carbon nanotubes, had a larger impact on the peak of the heat release rate, decreasing it by 16% and 17%, respectively. The samples with graphite, expandable graphite, and carbon fibers, decreased the peak of the heat release rate by 10%, 6%, and 11%, respectively. The total heat release decreased slightly for all the samples, except for the carbon fibers–wood‐plastic composite. The effective heat of combustion decreased also slightly, and carbon monoxide production increased for all the studied composites. Copyright © 2015 John Wiley & Sons, Ltd.     

Mechanical properties of carbon fiber/vinylester composites exposed to marine environments

The effects of seawater exposure on the mechanical properties of unidirectional T700 carbon fiber/vinylester (510A) composites have been examined. Carbon fibers with two different types of sizings (F and G) were studied. Dynamic mechanical analysis testing of the neat resin and a carbon/vinylester composite revealed similar viscoelastic responses and glass transition temperatures indicating same type of cured resin for both cases. An analysis of moisture absorption dynamics of the composites revealed Fickian behavior. The composites absorbed more moisture than the resin. The moisture up‐take in the composites is dominated by the fiber/matrix region. A comprehensive mechanical test program involving tension, compression, and shear tests was conducted on the composites at dry and saturated conditions. Composites with F‐sized carbon fibers displayed overall higher strengths than those with G‐sized fibers at both dry and moisture‐saturated conditions. Moisture absorption was found to have a moderate influence on most composite strengths, except for the in‐plane and interlaminar shear strengths, where reductions in the range of 10–16% occurred. POLYM. COMPOS., 35:1559–1569, 2014. © 2013 Society of Plastics Engineers     

Coextruded PVC/wood‐flour composites with WPC cap layers

Wood‐plastic composites (WPCs) can absorb moisture in a humid environment owing to the hydrophilic nature of the wood, thereby making the products susceptible to microbial growth and loss of mechanical properties. In this study, rigid poly(vinyl chloride) (PVC)/wood‐flour composites (core layer) were coextruded with either unfilled rigid PVC (cap layer) or rigid PVC filled with a small amount (5–27.5%) of wood flour (composite cap layers) in order to decrease or delay the moisture uptake. The thickness of the cap layer and its composition in terms of wood flour content were the variables examined during coextrusion. Surface color, moisture absorption, and flexural properties of both coextruded and noncoextruded (control) composite samples were characterized. The experimental results indicated that both unfilled PVC and composite cap layers can be encapsulated over rigid PVC/wood‐flour composites in a coextrusion process. The moisture uptake rate was lower when a cap layer was applied in the composites, and the extent of the decrease was a strong function of the amount of wood flour in the cap layer but insensitive to cap layer thickness. Overall, coextruding PVC surface‐rich cap layers on WPCs significantly increased the flexural strength but decreased the flexural modulus as compared with those of control samples. The changes in bending properties were sensitive to both cap layer thickness and wood flour content. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers     

Dynamic mechanical properties of extruded nylon–wood composites

Dynamic mechanical properties determine the potential end use of a newly developed extruded nylon–wood composite in under‐the‐hood automobile applications. In this article, the dynamic mechanical properties of extruded nylon–wood composites were characterized using a dynamic mechanical thermal analyzer (DMTA) to determine storage modulus, glass transition temperature (T_g), physical aging effects, long‐term performance prediction, and comparisons to similar products. The storage modulus of the nylon–wood composite was found to be more temperature stable than pure nylon 66. The T_g range of the nylon–wood composite was found to be between 23 and 56°C, based on the decrease in storage modulus. A master curve was constructed based on the creep curves at various temperatures from 30 to 80°C. The results show that the relationship between shift factors and temperature follows Arrhenius behavior. Nylon–wood composites have good temperature‐dependent properties. Wood fillers reduced the physical aging effects on nylon in the wood composites. The comparison of the nylon–wood composite with other similar products shows that nylon–wood composites are a promising low cost material for industrial applications. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Expansion mechanisms of plastic/wood‐flour composite foams with moisture,dissolved gaseous volatiles,and undissolved gas bubbles

The large quantity of moisture in wood‐flour may lead to the deterioration of the cell structure of foamed plastic wood‐flour composites in terms of cell size, non‐uniformity, and poor surface quality. Since these anomalies can cause poor mechanical properties of the foamed composites, the removal of the moisture from wood‐flour becomes a critical issue with respect to the improvement of these properties. The wood‐flour in this experimental study was first oven‐dried at different temperatures and then subjected to acetone extraction and thermogravimetric analysis (TGA). The oven‐dried wood‐flour was blended with plastic and then subjected to extrusion foaming. The results obtained from the TGA studies indicate that most volatiles were released from the extractives. Conversely, a comparative experimental study of the foaming behavior of these plastic/wood‐flour composites versus that of undried wood‐flour composites confirms that removal of the adsorbed moisture from wood‐flour results in a better cell morphology. However, it seems that some gaseous emissions released from wood‐flour are soluble in plastic and thereby favorably contribute to the development of the cell morphology. This paper describes the expansion mechanisms of wood‐flour composite foams resulting from the adsorbed moisture and dissolved gaseous emissions as well as resulting from the finely dispersed undissolved gas bubbles released from a chemical blowing agent.     

Effects of fiber size on short‐term creep behavior of wood fiber/HDPE composites

When natural fiber‐thermoplastic composites are used in long‐term loading applications, investigating creep behavior is essential. The creep behavior of high‐density polyethylene (HDPE)‐based composites reinforced with four sizes of wood fibers (WFs) (120–80, 80–40, 40–20, and 20–10 mesh) was investigated. The instantaneous deformation and creep strain of all WF/HDPE composites increased at a fixed loading level when the temperature was increased incrementally from 25 to 85°C. At a constant loading level, composites containing the larger‐sized WFs had better creep resistance than those containing smaller‐sized fibers at all measured temperatures. The creep properties of composites with smaller‐sized WFs were more temperature‐dependent than those with larger‐sized WFs. Two creep models (Burger's model and Findley's power law model) were used to fit the measured creep data. A time–temperature superposition principle calculation was attempted for long‐term creep prediction. The Findley model fitted the composite creep curves better than the four‐element Burger's model. From the predicted creep response of the WF/HDPE composites, two groups of small fibers (120–80 and 80–40 mesh) had the lowest creep resistance over long periods of time at the reference temperature of 25°C. The largest WFs (10–20 mesh) provided the best composite creep resistance. POLYM. ENG. SCI., 55:693–700, 2015. © 2014 Society of Plastics Engineers