Boudewijn J. R. Scholtens

Influence of the film former on fibre-matrix adhesion and mechanical properties of glass-fibre reinforced thermoplastics

Abstract The film former is in mass percentage the main component in most glass fibre sizes. Its influence on the fibre-matrix adhesion and the compound properties is studied in two thermoplastic matrices, i.e. polypropylene (PP) and rubber-modified styrene-co-maleic anhydride. The composition of the size is varied by changing the chemical nature and molecular mass of the film former and by leaving out the silane. The sizes morphology on the glass fibres is studied with scanning electron microscopy and X-ray photoelectron spectroscopy. The effect on fibre-matrix adhesion is inferred from 0° bending and interlaminar shear strength measurements of unidirectional, continuous fibre reinforced composites. The possible effect of the film former on matrix crystallinity in PP is studied with differential scanning calorimetry and polarized-light microscopy. The same sizes are also tested in injection moulded, short fibre reinforced compounds by measuring their mechanical properties. In addition, the diffusion of ...

Theoretical treatment of network formation by a multistage process

SummaryA general scheme for a multistage process of network formation is formulated in which the Galton-Watson or universal consistency relation is assumed to be valid. The scheme is elaborated with the theory of branching processes with cascade substitution. Cyclization is postulated not to occur, substitution effects are allowed and can be incorporated in the probability generating functions (pgf).

Nonlinear Viscoelastic Analysis of Uniaxial Stress‐Strain Measurements of Elastomers at Constant Stretching Rates

Two mathematical methods are presented to analyze uniaxial stress‐strain measurements of amorphous polymeric materials at constant stretching rates. Both methods are based on a well‐known single integral constitutive equation in which the time and strain effects are separated. The first approach results in an analytical equation and is only valid for materials of which the relaxation rate and nonlinearity are restricted. The second method is based on a numerical evaluation of the integral, and is exact for infinitesimal summation steps. Both methods enable the nonlinearity of the strain tensor to be determined if the linear viscoelastic behavior of the material is known.

Nonlinear Viscoelasticity of Noncrystalline EPDM Rubber Networks

An experimental study has been carried out to specify the nonlinear viscoelastic behavior of noncrystalline peroxide‐cured EPDM networks covering a range in elongation ratios between one and seven. Stress‐strain curves, measured at constant rates of elongation at 300, 345, and 390 K, are analyzed with two recently published methods. Time and strain effects are shown to be separable. The nonlinear strain measure, determined at various stretching rates, is studied as a function of temperature, cross‐link density, and prepolymer type. These results are compared with the strain measures of two phenomenological theories, namely with the Mooney‐Rivlin equation and a constitutive equation which contains the nonlinear n measure of strain, and with the predictions of the molecular theory of elasticity of polymer networks developed by Flory.

An IGC Study of Interactions in SAN/SMA Blends

Abstract Inverse gas chromatography has generated surface energy and acid-base interaction data for copolymers of styrene/acrylonitrile (SAN) and styrene maleic anhydride, (SMA) at mole per-cent compositions of SAN-26, SMA-26, and SMA-18. Also measured were polymer pair interaction data for 1:1 weight ratio blends of the copolymers. Explicit values of the X interaction parameter over wide temperature ranges also were obtained from these experiments. SAN was shown to be amphoteric, while SMA polymer surfaces interact as bases. The surface and bulk compositions differ both in single copolymers and polymer blends, with an excess of styrene moieties at surfaces and interfaces resulting from thermodynamic drives to minimize the relevant energies. Miscibility-immiscibility relationships in polymer blends are strongly temperature-dependent. Blends were shown to be miscible below glass transition temperatures, and again at temperatures above about 190°C, with immiscible conditions between these temperature ranges.

Time-temperature superposition and linear viscoelastic behaviour of EPDM networks with various degrees of crosslinking

SummaryConventional time-temperature (t-T) superposition appears to be inappropriate to the viscoelastic behaviour of amorphous, peroxide cured EPDM networks. A phenomenological approach is presented that reduces these permanent elastomers to thermorheologically simple materials. Although the origin of the anomalous behaviour observed is not yet completely understood, it is attributed to an unusual variation of the equilibrium modulus with temperature.

Synthesis of α-hydroxy-ω-amino poly(ethylene oxide) and its use in reaction injection moulding (RIM)

SummaryComputer simulations show that oligomers with two different terminal groups with dissimilar reactivities for isocyanates give a delayed viscosity rise in polyurethanes. This is a desired behaviour for RIM processes. Therefore, an α-hydroxy-ω-amino poly(ethylene oxide) (HAPEO) has been prepared. The synthesis was carried out by the ethoxylation of 2-hydroxyethyl phthalimide as a blocked amine. Hydrazinolysis appears to be the best way to obtain the deblocked oligomer. The product properties were compared with an oligomeric diamine ether (Jeffamine D2000). The gel time of HAPEO (Mn=500) and JAD2000 (Mn=2000) was the same (2 sec.). The product with HAPEO had a higher modulus, a comparable impact and tensile strength and a lower elongation at break.

Open Questions on Effects of Fibre-Matrix Interactions on Compound and Composite Properties

Compounds are short (∼ 0,3 mm) or long (> 0.6 mm) fibre reinforced thermoplastic or thermoset polymeric materials, which are processed automatically (injection or compression moulding), have good (mechanical) properties (for automotive, electric and electronic applications) and are relatively cheap. Composites contain continuous fibres (rovings, fabrics or mats), usually combined with thermosets, have excellent mechanical (structural) properties, but are very expensive because lack of an industrial process (mainly used in aerospace and aircraft industry).

Theoretical Treatment of Network Formation in a Three-Stage Process

A stochastic description of network formation in a three-stage process has recently been derived with the theory of branching processes with cascade substitution [1,2]. The distributions of units in the different reaction states are calculated with differential equations, so that substitution effects may be incorporated. Some preliminary results based on this theory are presented in this contribution.

Nonlinear Viscoelasticity of EPDM Networks

The nonlinear viscoelastic behaviour of noncrystalline EPDM networks has been studied at different tensile velocities and measuring temperatures, for various crosslink densities and prepolymers.