J.-A. E. Månson

Dendritic hyperbranched polymers as tougheners for epoxy resins

Reference LTC-ARTICLE-1999-002doi:10.1016/S0032-3861(98)00464-9View record in Web of Science URL: http://www.sciencedirect.com/science/journal/00323861 Record created on 2006-06-26, modified on 2016-08-08

Life Cycle Assessment of Biofibres Replacing Glass Fibres as Reinforcement in Plastics

This article aims to determine the environmental performance of China reed fibre used as a substitute for glass fibre as reinforcement in plastics and to identify key environmental parameters. A life cycle assessment (LCA) is performed on these two materials for an application to plastic transport pallets. Transport pallets reinforced with China reed fibre prove to be ecologically advantageous if they have a minimal lifetime of 3 years compared with the 5-year lifetime of the conventional pallet. The energy consumption and other environmental impacts are strongly reduced by the use of raw renewable fibres, due to three important factors: (a) the substitution of glass fibre production by the natural fibre production; (b) the indirect reduction in the use of polypropylene linked to the higher proportion of China reed fibre used and (c) the reduced pallet weight, which reduces fuel consumption during transport. Considering the whole life cycle, the polypropylene production process and the transport cause the strongest environmental impacts during the use phase of the life cycle. Since thermoplastic composites are hardly biodegradable, incineration has to be preferred to discharge on landfills at the end of its useful life cycle. The potential advantages of the renewable fibres will be effective only if a purer fibre extraction is obtained to ensure an optimal material stiffness, a topic for further research. China reed biofibres are finally compared with other usages of biomass, biomaterials, in general, can enable a three to ten times more efficient valorisation of biomass than mere heat production or biofuels for transport.

A review of dendritic hyperbranched polymer as modifiers in epoxy composites

Dendritic hyperbranched polymers have been shown to be able to double the interlaminar fracture resistance of epoxy-based composites and to reduce the internal stress level by as much as 80% with only 10 phr of modifier. These property improvements were obtained without affecting the viscosity, and thus the processability, nor the glass transition temperature of the epoxy resin. In the investigation, both fully soluble and phase-separating epoxy-functionalised hyperbranched polymers were used, the latter showing more efficient toughening properties. In these blend formulations, however, a close control of the phase separation mechanism was required, in order to avoid filtering effects before or during fibre impregnation. In composite plaques, the phase separation was investigated as a function of fibre surface treatment. In a few cases, a heterogeneous nucleation of modifier particles occurred at the fibre surface as a consequence of favoured fibre/particle interactions. This reduced the fibre/matrix bonding strength and led to adhesive failures at the fibre/matrix interface. In using dendritic hyperbranched polymer modifiers, maximum toughness enhancement and internal stress reduction, were thus obtained when the modifier nucleated within the matrix phase and adhesive failure at the fibre/matrix interface was avoided by selecting suitable fibre surface treatments.

Adhesion of silicon oxide layers on poly(ethylene terephthalate). I: Effect of substrate properties on coating's fragmentation process

Reference LTC-ARTICLE-1997-008View record in Web of Science URL: http://www3.interscience.wiley.com/cgi-bin/jhome/36698 Record created on 2006-06-26, modified on 2016-08-08

Residual stress build-up in thermoset films cured above their ultimate glass transition temperature

The stress build-up during isothermal cure below the ultimate glass transition temperature of epoxy and acrylate films is investigated in detail. Four systems are studied; two acrylates and two epoxies, with different crosslink densities. Relaxation modulus and film shrinkage are measured simultaneously during cure. The stress build-up is measured independently using a bi-layer beam bending technique. A model for the build-up of cure stresses is proposed, in which stresses are generated by the cure shrinkage and decay by viscoelastic relaxation. The relaxation is described by a simple, modified Maxwell model. Owing to the absence of memory in the Maxwell model, the resulting equation is simple and numerical stress computation straightforward. The stress build-up over time is thus simulated for the four model systems based on the relaxation and shrinkage data, and the simulations compared with the experimentally observed stress build-up. The model successfully predicts the cure stresses where more standard elastic methods fail. It is found that the amount of stress build-up during cure varies greatly between the different systems. In general, a higher crosslink density results in higher stress build-up. The stress on cure ranged from less than 1% of the total stress on cure and cool-down in a lightly crosslinked epoxy to more than 30% of the total stress in densely crosslinked epoxies and acrylates. Finally simple approximations for estimating the stress levels after cure and cool-down from basic material properties, e.g. modulus and cure shrinkage, are proposed.

Adhesion of silicon oxide layers on poly(ethylene terephthalate). II: effect of coating thickness on adhesive and cohesive strengths

Reference LTC-ARTICLE-1997-007View record in Web of Science URL: http://www3.interscience.wiley.com/cgi-bin/jhome/36698 Record created on 2006-06-26, modified on 2016-08-08

Prediction of Process-Induced Residual Stresses in Thermoplastic Composites

A model to predict the macroscopic in-plane residual stress state of semi crystalline thermoplastic composite laminates induced by process cooling is presented. Heat transfer during processing is based upon an incremental transient formulation that consists of a finite difference heat transfer analysis coupled to the crystallization kinetics. Micromechanics is used to evaluate the instantaneous spatial variation of mechanical prop erties as a function of temperature and degree of crystallinity. Residual stresses are based upon an incremental laminate theory that includes temperature gradients, shrinkage due to crystallization and thermal contraction. Temperature dependent relaxation times are used to model first order viscoelastic effects. A parametric study is conducted to explore the sensitivity of residual stresses to process history. Input parameters varied include surface temperature history (cooling rate), the amount of shrinkage caused by crystallization and the relaxation time at the reference temperature. The model predictions were in good agreement with experimental residual stress measurements for unidirectional graphite (AS4) reinforced polyetheretherketone (PEEK) laminates.

Reactive processing of poly(ethylene terephthalate) modified with multifunctional epoxy-based additives

Keywords: poly(ethylene terephthalate) ; epoxy-additives ; reactive processing Reference LTC-ARTICLE-2000-006doi:10.1016/S0032-3861(99)00768-5View record in Web of Science URL: http://www.sciencedirect.com/science/journal/00323861 Record created on 2006-06-26, modified on 2016-08-08

Impregnation technology for thermoplastic matrix composites

Abstract This paper reviews the technology available for the impregnation of carbon and glass fibres with thermoplastic resins. Process models and the key material factors influencing the achievement of impregnation are outlined, then the processes by which impregnation is currently carried out are discussed. These techniques can be divided into three categories: direct melt, processes where there is intimate mingling of the solid constituents prior to melting of the resin, and operations where low resin viscosities are employed (solvent impregnation and processes involving reactive chain extension).

Novel pulp fibre reinforced thermoplastic composites

The reinforcement potential of pulp fibres is presently not fully explored in thermoplastic composites. One of the reasons is that currently used processing methods comprise several severe thermomechanical steps inducing premature degradation of the fibres. Three pre-forming techniques were developed to prepare pulp fibre reinforced cellulose diacetate (CDA) pre-forms, namely filtration-forming, solvent impregnation, and commingling with polymer fibres. These techniques eliminate all thermomechanical steps, prior to final processing. The CDA polymer was nevertheless found to be very sensitive to the specific process histories relevant to each technique, contrary to the pulp fibres, whose size, shape, and mechanical properties were not affected by neither of the pre-forming processes. The tensile properties of composites compression moulded from solvent impregnated pre-forms were compared to those of ground china reed reinforced CDA. Whereas ground china reed particles were found to act merely as fillers increasing composite stiffness, a remarkable reinforcement effect was observed for the pulp fibre reinforced impregnated pre-forms. A combination of a stiffness increase by a factor 5.2 and a strength increase by a factor of 2.3 relative to the pure polymer was achieved, whereas in typical pulp fibre reinforced thermoplastics, the stiffness increase is frequently obtained at the expense of loss in strength. This work highlights the key factors which control the mechanical performance of pulp fibre reinforcements previously neglected in literature, and demonstrates the remarkable reinforcement potential of such renewable material. Furthermore, the properties achieved by optimising the extraction and processing steps indicate that pulp fibre reinforced thermoplastics composites are appropriate materials for load bearing applications.