Influence of the wood fibre filler on the internal recycling of poly(vinyl chloride)-based composites

The recycling of internal waste of poly(vinyl chloride) (PVC) and wood fibre-reinforced PVC composite was investigated and compared. Twenty extrusion-milling cycles were performed and the mechanical and thermal properties evaluated. This comparison provided evidence of the influence of the vegetable fibres on the thermo-mechanical degradation of the composite material. Up to five cycles, the composite properties remained stable. But after 10 cycles and especially at 20 cycles, the flexural strength increased, whereas the other mechanical properties remained almost constant. At the same time, a decrease of the degradation temperature revealed a deterioration of the molecular structure. The PVC properties remained constant, whereas a great increase in the impact strength was observed after 20 cycles without deterioration of the molecular structure. The different behaviours between the composite and the PVC were explained by the influence of the fibres, which accelerated the PVC degradation, characterized by dehydrochlorination followed by crosslinking reactions.     

Investigations on the recycling of hemp and sisal fibre reinforced polypropylene composites

Microscopic, mechanical, rheological and thermal tests were carried out in order to determine the recycling behaviour of PP/vegetal fibre composites. Different composites using hemp and sisal were characterized. All results were compared with PP-g-MA/hemp composites and PP/glass fibre composites.The results prove that mechanical properties are well conserved with the reprocessing of PP/vegetal fibre composites but that there is poor adhesion between the fibres and PP without any treatment. The addition of PP-g-MA shows an improvement of the bonding evidenced by MEB pictures. Vegetal fibres induce an increase in the percentage of crystallinity χ_c and in the crystallization temperature T_c which can be explained by the nucleating ability of the fibres improving crystallization of PP. The Newtonian viscosity η₀ decreases with cycles, indicating a decrease in molecular weight and chain scissions induced by reprocessing. The decrease of fibre length with reprocessing could be another reason for viscosity decrease.     

Rigidity analysis of polypropylene/vegetal fibre composites after recycling

Polypropylene/hemp or sisal fibre composites exhibit interesting recyclability [Bourmaud A, Baley C. Investigations on the recycling of hemp and sisal fibre-reinforced polypropylene composites. Polymer Degradation and Stability 2007;92(6):1034-45]. The obtained results prove that the tensile modulus of these polypropylene/vegetal fibre composites is well conserved with the number of reprocessing cycles. In this work, we investigated the relationship between the mechanical properties of the fibres and those of the composites by taking the influence of the recycling into account.In the first part of this study we carried out nanoindentation and tensile tests on vegetal fibres to obtain transversal and longitudinal Young's moduli. The experimental values were then introduced into micromechanical models, taking the aspect ratio changes into account, to estimate the stiffness of the PP/vegetal fibre injected composites before and after recycling. The first results show an interesting correlation between experimental results and model predictions; however a general underestimation of tensile stiffness of composites can be noticed.     

Polymer matrix influence on stability of wood polymer composites

The aim of the presented work is to show the influence of the various polymer matrices and the different amounts of the cellulose filler on the composites properties. Samples based on polypropylene, polystyrene, polyoxymethylene, acrylonitrile butadiene styrene, polyester resin, and polylactic acid with different contents of cellulose fibers were prepared by injection molding process. The mechanical and dielectric properties of these composites were studied in order to check whether investigated wood polymer composites fulfill requirements for their application in electrical devices. For all tested composites, a linear increase of modulus with cellulose content was observed. Addition of cellulose to the tested polymers significantly reduces strain at break. In the case of polypropylene and polyoxymethylene composites, the tensile strength increases with the content of the filler. For other materials, there is an inverse relationship, namely the addition of cellulose decreases the tensile strength. The electrical strength decrease was observed with increased cellulose content for the majority of the investigated composites. Polar groups incorporated by cellulose fibers have led to dielectric constant increase. Furthermore, aging of composites in mineral oil and evaluation of water uptake for wood–plastic samples were performed. Wood polymer composites have changed significantly after aging. The water diffusion coefficients were determined, and the significant influence of the amount of cellulose on the water absorption was shown. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of thermal-treatment of wood fibres on properties of flat-pressed wood plastic composites

This study aimed to enhance the dimensional stability of flat-pressed wood plastic composites (WPCs) containing fast growing wood fibres by a thermal-treatment method. The wood fibres were treated at three different temperatures (120, 150, or 180 °C) for 20 or 40 min in a laboratory autoclave. The WPC panels were made from dry-blended Eucalyptus camaldulensis wood fibres and polypropylene (PP) powder (50:50 by weight) using a conventional flat-press process under laboratory conditions. Thickness swelling and water absorption of the WPC panels significantly decreased with increasing the treatment temperature and time. The thermal-treatment of eucalyptus wood fibres slightly decreased the screw withdrawal resistance of the WPC panels as compared to the reference panels while the flexural properties and internal bond strength were more seriously affected by the treatment. The present study revealed that the thermal-treatment of the wood fibres significantly improved the dimensional stability of the WPC panels.     

The influence of interphases on properties of epoxy resin composites

Water sorption was determined and dynamic-mechanical measurements made on dry and water-containing systems. Different types of surface treatments of the glass fiber were studied. Immobilization of polymer chains in the interphase is determined by the nature of the curing system, annealing conditions, and surface treatment of glass fibers. Penetrating water can be found at three kinds of locations in the composite; water in the interphase has different properties than water in the polymer matrix and in microvoids. This fact can be used as a microscopic probe in epoxy-containing composites. Water content depends on the density of polar groups and the density of the network. At higher temperatures water causes crazes, at lower it mainly acts as a plasticizer. Water in crazes does not affect the glass transition temperature Tg, but it decreases (tan δ) and weakens the material. As long as water mainly goes into swelling, energy transfer between the resin and the matrix is not affected. The reinforcement then works as it should. The results demonstrate the importance of interphase properties on the behavior of the composite.     

Accelerated weathering of unbleached and bleached Kraft wood fibre reinforced polypropylene composites

In this paper, combined moisture/ultraviolet (UV) weathering performance of unbleached and bleached Kraft wood fibre reinforced polypropylene (PP) composites was studied. Composites containing 40 wt% fibre with 3 wt% of a maleated polypropylene (MAPP) coupling agent were fabricated using extrusion followed by injection moulding. Composite mechanical properties were evaluated, before and after accelerated weathering for 1000 h, by tensile and impact testing. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were also carried out to assess the changes occurring during accelerated weathering. Bleached fibre composites initially showed higher tensile and impact strengths, as well as higher thermal stability and greater crystallinity. During accelerated weathering, both unbleached and bleached fibre composites reduced tensile strength (TS) and Young's modulus (YM), with the extent of the reduction found to be similar for both unbleached and bleached fibre composites. Evidence supported that the reduction of TS and YM was due to PP chain scission, degradation of lignin and reduced fibre-matrix interfacial bonding.     

Development of ceramic-matrix composites — A challenge to chemistry

In this contribution the state-of-the-art of ceramic-matrix composites is briefly summarized. A critical review of the different types of ceramic composites is given, particularly emphasizing the challenge to chemistry. As example two important problem areas, which may only be solved by contributions from chemistry, are discussed: some low- temperature processing techniques for ceramic composites which avoid damage of fibres by thermal or mechanical loading and/or by chemical reactions as well as the optimization and control of interfaces.     

The influence of surface treatment on the tensile and tribological properties of wood fiber‐reinforced polyimide composite

In this paper, the effect of coupling agent surface treatment of wood fiber on tensile and tribological property of wood fiber‐reinforced thermoplastic polyimide (PI) composites was experimentally investigated. Experimental results revealed that coupling agent surface treatment could effectively improve the interfacial adhesion between wood fiber and PI matrix. Compared with the untreated wood fiber/PI composite, the coupling agent‐treated composite had better interfacial adhesion. The fracture surfaces and worn surface of samples were investigated by scanning electronic microscopy to analyze the effects of surface treatment methods.     

Physical properties of PVC/aminosilane‐treated wood flour/organoclay composites

Most physical properties of a wood plastic composite (WPC) with poly(vinyl chloride) (PVC) matrix are lower than those of corresponding neat PVC because of poor interfacial adhesion between hydrophobic PVC and hydrophilic wood. In this study, to improve the interfacial adhesion, wood flour was pre‐treated with N‐2(aminoethyl)‐3‐aminopropyltrimethoxysilane, and the surface modification was characterized and confirmed by X‐ray photoelectron spectroscopy (XPS). Furthermore, to improve the performance of PVC/wood composites, a type of organoclay was added as nanofiller. PVC/wood/clay composites were prepared by melt blending a heavy metal‐free PVC compound, the aminosilane‐treated wood flour, and the organoclay, and their physical properties were tested by universal testing machine and thermal gravimetric analyzer. X‐ray diffractometer (XRD) analyses of the WPCs showed an intercalated structure of the organoclay. The scanning electron microscope images for the fracture surfaces of the WPCs confirmed the positive effect of the aminosilane pre‐treatment by showing reduced debonding of wood flour from the PVC matrix. The performance of the WPCs was improved by the aminosilane pre‐treatment of the wood flour and the organoclay. Copyright © 2011 John Wiley & Sons, Ltd.     

Possible influence of electron — lattice interactions on the Verwey transition in magnetite

In the paper crystal lattice influence on the Verwey transition in magnetite related compounds is discussed based on the experimental activity of our group. Heat capacity studies indicate the distinct low temperature lattice properties of slightly doped magnetite from those with higher dopant concentration. Neutron scattering lattice examination and the elastic constants studies are then performed to further study this conjecture. Our main conclusion is that the Verwey transition in magnetite can not be understood and described without strong involvement of lattice dynamics.     

Performance of polypropylene–wood fiber composites

Polypropylene–wood fiber composites were prepared in the optimal mixture conditions determined in a previous work (180°C, 60 rpm, 10 min). Tensile, impact and three-point bending tests were performed in order to evaluate the adhesion between matrix and wood fibers. Other than mixture conditions, drying temperature of treated wood fiber is also an important factor to obtain good performance composites as shown in this work. Tensile properties of composites submitted to two extreme conditions (immersion in water at ambient temperature for 90 days and immersion in boiling water for 1 h) were determined. Heat deflection temperature and thermal analysis of composites were evaluated.     

Rheological properties of wood polymer composites at high shear rates

This paper presents the rheological properties of wood-polymer composites (WPC) with a polypropylene (PP) matrix in the corrected shear rate range from approx. 20 s⁻¹ to 150 000 s⁻¹. Tests were conducted using a capillary rheometer and a rheological head of the author's construction, for which the working element is a thermoplastic injection moulding machine. The constructed tool was found to be very useful, especially for the determination of the processing characteristics of WPC composites containing a large particle-size filler. It was observed that the rheological properties of wood-polymer composites in the shear rate range of up to several thousand s⁻¹ significantly depended on the filler content of the polymer matrix; at the same time, at higher shear rate, a clear decrease in the effect of the wood filler content on the viscosity of the composites and on the flow behaviour, as described by the power law, took place.     

Fire properties of silylated α‐zirconium phosphate composites based on polystyrene

α‐zirconium phosphate (ZrP) (prepared by both reflux and hydrothermal methods) is silylated with chlorotrimethylsilane and characterized by X‐ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. Polystyrene/silylated‐ZrP composites show higher thermal stability as the ZrP content increases. Cone calorimetry suggests that the reduction of the peak heat release rate of polystyrene (PS)/ZrP composites does not increase as the ZrP loading increases; the aspect ratio of ZrP has little effect in fire performance of PS/ZrP composites. Copyright © 2013 John Wiley & Sons, Ltd.     

Solvent-induced swelling of membranes — Measurements and influence in nanofiltration

This paper describes improvements to an apparatus for in-situ determinations of swelling where a linear inductive probe and electronic column gauge with an overall resolution of 0.1 μm was used for measurements of seven variants of polyacrylonitrile (PAN)/polydimethylsiloxane (PDMS) composite nanofiltration membranes in a range of alkane, aromatic and alcohol solvents. The unswollen membranes incorporated PDMS layers between 1 and 10 μm nominal thickness and were manufactured with a radiation and/or thermal crosslinking step.

The tested membranes exhibited a range of swelling dependent on the degree of crosslinking, the initial PDMS layer thickness and the type of solvent. With no applied pressure the PDMS layer on some radiation cross-linked membranes swelled as much as 170% of the initial thickness whilst other membranes were restricted to a maximum swelling of 80%. When a pressure up to 2000 kPa was applied to a membrane then swelling could be reduced to 20% of the value obtained at zero applied pressure. By vertically stacking up to three membrane samples it was possible to determine the swelling of PDMS layers as thin as 1 μm, although higher imposed pressures rendered some results unreliable as the measurement resolution of the apparatus was approached. The results of the swelling experiments are contrasted with crossflow nanofiltration performance in terms of solvent flux and solute rejection.     

The influence of the recycling stress history on LDPE waste pyrolysis

It is elementary to recognize the benefits and the negative impacts of the use of plastic materials on modern societies. Polyethylene (PE) is the major plastic component present in the municipal solid waste. In this paper, two types of low-density PE (LDPE) waste with different mechanical recycling stress histories were used to investigate the influence of recycling cycles on pyrolysis. The kinetic triplet and thermal degradation study were obtained using TGA data.To determine the sample composition and hydrocarbon arrangements, ultimate, proximate and X-ray diffraction analyses were carried out. Taking advantage of these analyses and combining them with differential scanning calorimetry (DSC) data, a series–parallel pyrolysis pathway was formulated. The waste of recycled polyethylene presented low enthalpy of pyrolysis, at about 205 J/g against 299 J/g for a virgin PE. The DSC analyses evidenced a multi-step reaction behavior of the pyrolysis, confirmed by the kinetic study using different isoconversional methods: the waste of recycled polyethylene presented a higher variation of activation energies as a function of the fraction reacted. The main conclusion is that the results suggest that the recycling stress history promotes the increase of long carbon chains while weakening the boundary among the compounds. This explains the fact that recycled waste needs less activation energy than other samples to degrade thermally. Finally, different categories of low-density polyethylene wastes must be considered when dealing with either kinetics or modeling of the product recovery process.     

Thermoplastic composites based on flax fibres and polypropylene: Influence of fibre length and fibre volume fraction on mechanical properties

Natural-fibre-mat-reinforced thermoplastic (NMT) composites based on flax fibre mats and a Polypropylene (PP) matrix were manufactured using (i) a film-stacking method and (ii) a paper making process. The influence of fibre length and fibre content on stiffness and strength is reported and compared with data for glass-mat-reinforced thermoplastic (GMT) composites, including the influence of using maleic-anhydride grafted PP. The data is also compared with existing micromechanical models like Kelly-Tyson and Cox-Krenchel for strength and stiffness, respectively. A good agreement was found between theory and experiment in case of stiffness while in case of strength the experimental values fall well below the theoretical predictions. Results indicated that NMTs are of interest for low-cost engineering applications and can compete with commercial GMTs, especially when a high stiffness per unit weight is desirable. Results also indicated that the key area for future development lies not only in improved adhesion but mainly in improving the fibre strength.