Mold susceptibility of rigid PVC/wood‐flour composites

Rigid PVC/wood‐flour composite lumber containing either hardwood (maple) or a softwood (southern pine) wood flour at different levels of wood‐flour content was evaluated for susceptibility to fungal colonization and discoloration by using standard tests that mimicked exterior (ASTM G21) and interior (ASTM D3273) environments, respectively. In the exterior test protocol, although both types of PVC/wood‐flour composite lumber exhibited fungal colonization and discoloration, the composites containing maple exhibited greater discoloration than those containing pine. Irrespective of wood species, fungal colonization and discoloration in the composite lumber were greater at the bottom faces where they were in constant contact with moisture. The wood content range (50–100 phr) used in this study showed no effect on extent of fungal colonization and discoloration. All composites showed no discoloration in the interior test protocol. Both optical microscopy and environmental scanning electron microscopy clearly demonstrated that wood flour particulates are not completely encapsulated by the PVC matrix, so that exposed wood flour in the surface crevices of the composite lumber may serve as points of moisture sorption and staging points for fungal colonization and discoloration. J. Vinyl Addit. Technol. 10:179–186, 2004. © 2004 Society of Plastics Engineers.     

Microcellular foaming of impact‐modified rigid PVC/wood‐flour composites

Solid state microcellular foaming technology was employed to investigate the influence of impact modification on the foamability of neat rigid PVC and rigid PVC/wood‐flour composite samples. The effects of impact modifier types (crosslinked versus uncrosslinked) and concentrations on the void fraction of foamed samples were examined. The influence of impact modification on the sorption behavior of CO₂ in the samples was also studied. The experimental results indicate that impact modification accelerates the rate of gas loss during the foaming process, which impedes the growth of nucleated cells, independent of modifier type. Because of this accelerated gas loss, impact modification inhibits the potential of producing foamed samples with void fractions similar to those achieved in unmodified samples.     

Mechanical properties of extrusion‐foamed rigid PVC/wood‐flour composites

This study was conducted to characterize the mechanical properties of extrusion‐foamed neat rigid PVC and rigid PVC/wood‐flour composites by using endothermic and exothermic chemical foaming agents (CFAs). The specific elongation at break (ductility) of the samples was improved by foaming, while the opposite trend was observed for the tensile strength and modulus of the samples, regardless of the chemical foaming agent type. In addition, experimental results indicated that foaming reduced the Izod impact resistance of both neat rigid PVC and rigid PVC/wood‐flour composites but that this reduction was not statistically significant for the composites. A comparison between batch microcellular processing and extrusion foam processing was made, which demonstrated that foams with very fine cells (microcellular processed) exhibit better impact strength than foams with larger cells (extrusion processed with CFAs).     

Fusion characteristics of rigid PVC/wood‐flour composites by torque rheometry

This study was aimed at examining the effects of wood flour contents, wood species (softwood vs. hardwood), and particle size on the fusion characteristics (fusion time, fusion temperature, fusion torque, and fusion energy) of rigid PVC/wood‐flour composites in a torque rheometer. Neat rigid PVC exhibited one fusion peak, whereas the addition of wood flour into the PVC matrix led to two fusion peaks. Increased wood flour content caused a significant increase in the time, temperature, and energy at which fusion between the primary particles started, thereby leading to increased fusion torque, irrespective of the wood flour species. These results implied that rigid PVC filled with wood flour must be processed at higher temperatures than neat resin. Although fusion characteristics of the composites were influenced by the wood species, a clear trend between softwood and hardwood species could not be established. However, finer particles fused more quickly and needed less energy than coarse ones. J. VINYL ADDIT. TECHNOL., 13:7–13, 2007. © 2007 Society of Plastics Engineers.     

Effect of multi‐walled carbon nanotubes dispersity on the light transmittancy of multi‐walled carbon nanotubes/epoxy composites

Two types of multi‐walled carbon nanotubes (MWCNTs), chemically modified and unmodified, were dispersed in epoxy resin with ultrasonication. The light transmittance characteristics of epoxy composites with different ratios of MWCNTs to epoxy resin were measured at wavelengths ranging from 200 to 1100 nm. Results showed that composites with modified MWCNTs had a much higher light transmittance than those with unmodified MWCNTs. This was presumably due to a more uniform dispersion of modified MWCNTs in the epoxy matrix, as indicated by both transmission electron microscopy and optic microscopy. The wavelength dependency of light transmittance of the composites was expressed empirically as a function of weight fraction (f_w) of MWCNTs and the light wavelength (λ). POLYM. ENG. SCI. 46:635–642, 2006. © 2006 Society of Plastics Engineers.     

PVC/wood‐flour composites compatibilized with chlorinated polyethylene

Chlorinated polyethylene has been demonstrated to be an effective compatibilizer for dissimilar materials in various mixed‐polymer or recycled‐polymer systems. In this paper the use of chlorinated polyethylene to compatibilize polymer/natural‐fiber composites is discussed. Examples of applications in PVC/wood‐flour composites are given.     

Foaming of rigid PVC/wood‐flour composites through a continuous extrusion process

The effects of chemical foaming agent (CFA) types (endothermic versus exothermic) and concentrations as well as the influence of all‐acrylic processing aid on the density and cell morphology of extrusion‐foamed neat rigid PVC and rigid PVC/wood‐flour composites were studied. Regardless of the CFA type, the density reduction of foamed rigid PVC/wood‐flour composites was not influenced by the CFA content. The cell size, however, was affected by the CFA type, independent of CFA content. Exothermic foaming agent produced foamed samples with smaller average cell sizes compared to those of endothermic counterparts. The experimental results indicate that the addition of an all‐acrylic processing aid in the formulation of rigid PVC/wood‐flour composite foams provides not only the ability to achieve density comparable to that achieved in the neat rigid PVC foams, but also the potential of producing rigid PVC/wood‐flour composite foams without using any chemical foaming agents.     

Accelerated ultraviolet weathering of PVC/wood‐flour composites

Ultraviolet weathering performance of polyvinyl chloride (PVC) filled with different concentrations of wood flour was studied. Extruded PVC/wood‐flour composite samples were subjected to cyclic ultraviolet lamps/condensation exposures and assessed over a total of 400 and 2600 hours. Each assessment consisted of DRIFTFTIR and XPS collections, contact angle measurement, color measurement, and tensile property testing. The experimental results indicated that wood flours are effective chromophore materials since their incorporation into a rigid PVC matrix accelerated the degradation of the polymeric matrix. Photodegradation converted unfilled PVC samples to a colored material of lower extensibility. Although composite samples exhibited greater discoloration than unfilled PVC samples, they retained all their original strength and stiffness properties even after 2600 hours of cyclic UV irradiation/condensation exposures.     

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     

Preparation and properties of multi‐walled carbon nanotubes/carbon fiber/epoxy composites

Multi‐walled carbon nanotubes/carbon fiber (MWCNTs/CF) hybrid fillers are employed to prepare MWCNTs/CF/epoxy composites. Results reveal that a great improvement of the thermal conductivities of the epoxy composites with the addition of MWCNTs/CF hybrid fillers, and the thermal conductivity of the MWCNTs/CF/epoxy composites is 1.426 W/mK with 8 vol% treated MWCNTs/CF hybrid fillers (5 vol% MWCNTs + 3 vol% CF). Both the flexural and impact strength of the MWCNTs/CF/epoxy composites are increased firstly, but decreased with the excessive addition of MWCNTs. The flexural and impact strength of the MWCNTs/epoxy composites are optimal with 2 vol% MWCNTs. For a given MWCNTs/CF hybrid fillers loading, the surface treatment of MWCNTs/CF hybrid fillers can further increase the thermal conductivities and mechanical properties of the MWCNTs/CF/epoxy composites. POLYM. COMPOS., 35:2150–2153, 2014. © 2014 Society of Plastics Engineers     

Enhanced dielectric properties of polyamide 11/multi‐walled carbon nanotubes composites

Composites with multi‐walled carbon nanotubes (MWNTs) involved in polyamide 11 (PA11) were prepared via a conventional melt blending method. The structure, morphology, crystallization behavior, electrical, and dielectric properties of composites were investigated. The results demonstrated that the dispersed uniformly MWNTs favored the formation of α crystal of PA11 when the composites were quenched from melt. The dielectric constant of composites was dependent on the electric field frequency and MWNTs content, and the highest value of dielectric constant was as high as 350 for the composite with 1.21 vol % MWNTs at 10³ Hz, accompanied by a low dielectric loss. The enhanced dielectric properties could be interpreted by the formation of abundant nanocapacitors within the composites and the interfacial polarization effect resulting from accumulation of charge carriers at the internal interfaces between MWNTs and PA11. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42642.     

Photoaging and stabilization of rigid PVC/wood‐fiber composites

Ultraviolet (UV) weathering performance of unpigmented and rutile titanium dioxide pigmented rigid polyvinyl chloride (PVC)/wood‐fiber composites has been studied. The composite samples were manufactured by dry‐blending PVC, wood fibers, and other processing additives in a high‐intensity mixer. The dry‐blended compounds were extruded and compression molded into panel samples. The manufactured samples were artificially weathered using laboratory accelerated UV tests. Composite samples were exposed to 340‐nm fluorescent UV lamps and assessed every 200 h, for a total of 1200 h of accelerated weathering. Each assessment consisted of a visual examination of surface roughness or erosion, a contact angle measurement, a FTIR collection, and a color measurement. The experimental results indicated that wood fibers are effective sensitizers and that their incorporation into a rigid PVC matrix has a deleterious effect on the ability of the matrix to resist degradation caused ultraviolet irradiation. The light stability of these composites could be improved quite efficiently with the addition of rutile titanium dioxide photoactive pigment during formulation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1943–1950, 2001     

Novel coupling agents for PVC/wood‐flour composites *

Effective interfacial adhesion between wood fibers and plastics is crucial for both the processing and ultimate performance of wood–plastic composites. Coupling agents are added to wood–plastic composites to promote adhesion between the hydrophilic wood surface and hydrophobic polymer matrix, but to date no coupling agent has been reported for PVC/wood‐fiber composites that significantly improved their performance and was also cost‐effective. This article presents the results of a study using chitin and chitosan, two natural polymers, as novel coupling agents for PVC/wood‐flour composites. Addition of chitin and chitosan coupling agents to PVC/wood‐flour composites increased their flexural strength by ～20%, their flexural modulus by ～16%, and their storage modulus by ～33–74% compared to PVC/wood‐flour composite without the coupling agent. Significant improvement in composite performance was attained with 0.5 wt% of chitosan and when 6.67 wt% of chitin was used. J. VINYL ADDIT. TECHNOL., 11:160–165, 2005. © 2005 Society of Plastics Engineers     

Mechanical and surface properties of polyurethane/fluorinated multi‐walled carbon nanotubes composites

To improve the mechanical and surface properties of poly(etherurethane) (PEU), multi‐walled carbon nanotubes (MWCNTs) were surface grafted by 3,3,4,4, 5,5,6,6,7,7,8,8,8‐tridecafluoro‐1‐octanol (TDFOL) (MWCNT‐TDFOL) and used as reinforcing agent for PEU. Fourier‐transform infrared spectroscopy revealed the successful grafting of MWCNTs. PEU filled with MWCNT‐TDFOL could be well dispersed in tetrahydrofuran solution, and tensile stress–strain results and dynamic mechanical analysis showed a remarkable increase in mechanical properties of PEU by adding a small amount of MWCNT‐TDFOL. Contact angle testing displayed a limited improvement (just 9°) in the hydrophobicity of PEU surface by solution blending with MWCNT‐TDFOL. However, a large improvement of surface hydrophobicity was observed by directly depositing MWCNT‐TDFOL powder on PEU surface, and the water contact angle was increased from 80° to 138°. Our work demonstrated a new way for the modification of carbon nanotubes and for the property improvement of PEU. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Online measurement of rheological properties of PVC/wood‐flour composites

By using a factorial design approach, this study examined the effect of the component materials on the viscoelastic properties of PVC/wood‐flour composites. Statistical analysis was performed to determine the effects of wood‐flour content, acrylic modifier content, and plasticizer content on the die swell ratio and viscosity of the composites measured online on a conical twin‐screw extrusion capillary rheometer. The viscoelastic properties of the samples also were measured using dynamic mechanical analyzer (DMA). Wood‐flour content and acrylic modifier content were the two important variables affecting the die swell ratio, whereas the addition of a low level of plasticizer did not affect this ratio. The die swell increased with the increased acrylic modifier content, but it was reduced considerably by adding wood flour into the PVC matrix. The true viscosity of neat PVC and PVC/wood‐flour composites decreased with the plasticizer content, irrespective of the acrylic modifier content. However, the addition of acrylic modifier significantly increased the viscosity of unfilled PVC, while an opposite trend was observed for the composites, owing to the differing effect of acrylic modifier on the melt elasticity and viscosity of these materials. J. Vinyl Addit. Technol. 10:121–128, 2004. © 2004 Society of Plastics Engineers.     

Melt extrudate swell behavior of multi‐walled carbon nanotubes filled‐polypropylene composites

The extrudate swell behavior of polypropylene (PP) composite melts filled with multi‐walled carbon nanotubes (MWCNTs) was studied using a capillary rheometer in a temperature range from 190 to 230°C and at various apparent shear rates varying from 50 to 800 s⁻¹. It was found that the values of the extrudate swell ratio of the composites increased nonlinearly with increasing apparent shear rates, while the values of the extrudate swell ratio decreased almost linearly with increasing temperature. The values of the melt extrudate swell ratio increased approximately linearly with increasing shear stress, while decreased approximately nonlinearly with an increase of the MWCNT weight fraction. In addition, the extrudate swell mechanisms were discussed with observation of the fracture surface of the extrudate using a scanning electronic microscopy. This study provides a basis for further development of MWCNTs reinforced polymer composites with desirable mechanical and thermal properties. POLYM. COMPOS., 38:2433–2439, 2017. © 2015 Society of Plastics Engineers     

Effects of copper amine treatment on mechanical properties of PVC/wood‐flour composites

Copper amine–treated wood flour was added to PVC [poly(vinyl chloride)] matrix in order to manufacture PVC/wood‐flour composites. Effects of copper treatments on the mechanical properties of PVC‐wood composites were evaluated. Unnotched impact strength, flexural strength, and flexural toughness of the composites were significantly improved by the wood‐flour copper treatment. The optimum copper concentration range was 0.2 to 0.6 wt% of wood flour. Fractured surfaces were examined by using scanning electron microscopy (SEM) combined with energy‐dispersive spectroscopy (EDS). PVC/wood interfacial debonding was the main fracture mode of untreated wood‐flour composites, whereas wood‐particle pullout and breakage dominating the fractured surfaces of copper‐treated wood‐flour composites. On the fractured surfaces, more PVC could be found on the exposed copper‐treated wood particles than on untreated wood, a result suggesting improved PVC‐wood interfacial adhesion after copper treatments. J. Vinyl Addit. Technol. 10:70–78, 2004. © 2004 Society of Plastics Engineers.     

Preparation and characterization of polydiphenylamine/multi‐walled carbon nanotube composites

We describe the synthesis of methane sulfonic acid (MeSA)‐doped poly(diphenylamine) (PDPA) with carboxylic groups containing multi‐walled carbon nanotubes (c‐MWNTs) via in situ polymerization. Diphenylamine monomers were adsorbed on to the surface of c‐MWNTs and polymerized to form PDPA/c‐MWNT composites. SEM and TEM images indicated two different types of materials: the thinner fibrous phase and the larger globular phase. The individual fibrous phase had a diameter around 100–130 nm, which should be the carbon nanotubes (diameter 20–30 nm) coated with a PDPA layer. The structure of PDPA/c‐MWNT composites was characterized by FTIR, UV‐visible spectroscopy and X‐ray diffraction patterns. The electrical conductivities of PDPA/c‐MWNT composites were much higher than that of PDPA without c‐MWNTs. Copyright © 2006 Society of Chemical Industry     

Electrical and mechanical properties of multi‐walled carbon nanotubes reinforced PMMA and PS composites

The use of multi‐walled carbon nanotubes (MWCNT) as reinforcing material for thermoplastic polymer matrices, polymethyl methacrylate (PMMA), and polystyrene (PS) has been studied. MWCNT were synthesized by chemical vapor deposition (CVD) technique using ferrocene‐toluene mixture. As‐prepared nanotubes were ultrasonically dispersed in toluene and subsequently dispersed in PMMA and PS. Thin polymer composite films were fabricated by solvent casting. The effect of nanotube content on the electrical and mechanical properties of the nanocomposites was investigated. An improvement in electrical conductivity from insulating to conducting with increasing MWCNT content was observed. The carbon nanotube network showed a classical percolating network behavior with a low percolation threshold. Electromagnetic interference (EMI) shielding effectiveness value of about 18 dB was obtained in the frequency range 8.0–12 GHz (X‐band), for a 10 vol% CNT loading. An improved composite fabrication process using casting followed by compression molding and use of functionalized MWCNT resulted in increased composites strength. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Effects of impact modifiers on the properties of rigid PVC/wood‐fiber composites

This study examined the effects of impact modifier types and addition levels on the mechanical properties of rigid PVC/wood‐fiber composites. The impact resistance of rigid PVC/wood‐fiber composites depends strongly on the type and content of impact modifier. With the proper choice of modifier type and concentration, the impact strength of rigid PVC/wood‐fiber composites can be significantly improved without degrading the tensile properties. Methacrylate‐butadiene‐styrene and all‐acrylic modifiers performed in a similar manner and were more effective and efficient in improving the impact resistance of rigid PVC/wood‐fiber composites than the chlorinated polyethylene modifier.