Philippe Zinck

Role of silane coupling agent and polymeric film former for tailoring glass fiber sizings from tensile strength measurements

Tensile strengths of differently sized E-glass fibres have been characterised using a bimodal Weibull two parameters cumulative distribution function. By comparing unsized fibres, pure silanes, different film formers, and silane/film former combinations, a comprehensive summary on the healing effect for surface flaws in relation to the type of sizing emulsion has been obtained. The great influence of the film former, which is the main component of the sizing by weight, was shown to affect both the healing of initially occuring flaws in the unsized fibre and the possibility of creating new defects. Besides the single influence of the film former, the synergetic effect of silane and film former polymer has been shown. In fact, the presence of sizing influences both the population of flaws on the fibre surface and the structure of the interphase, which will be created from the impregnation with a polymer matrix. Data from statistics of fracture as a function of the nature of sizings were discussed according to the literature on stress corrosion of E-glass filaments.

Mechanical characterisation of glass fibres as an indirect analysis of the effect of surface treatment

Tensile strength of E-glass fibres have been analysed using a bimodal Weibull two parameter cumulative distribution function. The bimodal character were associated to surface and internal flaws, respectively. Influence of silane coating as well as industrial sizing on the flaws distribution was quantitatively characterised. A qualitative interpretation of their effect based on a combination of probabilistic and deterministic approaches were proposed in terms of crack healing. It was demonstrated there that mechanical testing of fibres can be used as an indirect observation technique of the consequences of the surface treatment. An analogy is proposed between the sizing treatment of glass fibres and the strengthening of silica glass by means of hybrid organic-inorganic coatings.

Catalytic Chain Transfer (co-)Polymerization : Unprecedented Polyisoprene CCG and a New Concept to Tune the Composition of a Statistical Copolymer

Borohydrido-halflanthanidocene/dialkylmagnesium combinations are found to be powerful catalytic systems for the chain transfer polymerization of isoprene and its copolymerization with styrene. A behavior close to a lanthanide catalyzed polyisoprene chain growth on magnesium is reported. Transmetalation is further shown to occur in the course of the statistical copolymerization of isoprene and styrene. For the same monomer feed, the amount of styrene inserted in the copolymer can be increased by a factor 3 using 10 equiv. dialkylmagnesium versus 1 in the range of our experimental conditions. Chain transfer in the course of a metal catalyzed statistical copolymerization may thus be viewed as a new and original way for the control of the composition of a copolymer.

Are microcomposites realistic models of the fibre/matrix interface? I. Micromechanical modelling

The ability of the microbond technique to characterise changes in the physico-chemical structure of the interface between fibre and matrix has been checked using eight epoxyde/glass fibre systems differing by their matrix chemistry, fibre surface treatments, and fibre diameter. It has been shown that the widely used average IFSS method can lead to biased results. The test is now considered as giving mode I or mixed-mode properties of the interface and not only a mode II interfacial toughness or interfacial shear strength (IFSS). Energy approaches are thus be preferred to stress criterion models. The suitability of six theoretical models was checked. Difficulties were found in determining a parameter or method effectively representative of the physico-chemical structure of the interface. The model providing the most reliable results was that of Scheer and Nairn. Significant plastic flow of the polymeric droplet was observed, leading to a questioning of the hypotheses of ideal elastic components.

Isoprene–Styrene Chain Shuttling Copolymerization Mediated by a Lanthanide Half-Sandwich Complex and a Lanthanidocene: Straightforward Access to a New Type of Thermoplastic Elastomers†

A lanthanide half-sandwich complex and a ansa lanthanidocene have been assessed for isoprene-styrene chain shuttling copolymerization with n-butylethylmagnesium (BEM). In the presence of 1 equiv BEM, a fully amorphous multiblock microstructure of soft and hard segments is achieved. The microstructure consists of poly(isoprene-co-styrene) blocks, with hard blocks rich in styrene and soft blocks rich in isoprene. The composition of the blocks and the resulting glass transition temperatures (Tg ) can be easily modified by changing the feed and/or the relative amount of the catalysts, highlighting a new class of thermoplastic elastomers (TPEs) with tunable transition temperatures. The materials self-organize into nanostructures in the solid state.

First polymer “ruthenium-cyclopentadienyl” complex as potential anticancer agent

d-glucose end-capped polylactide ruthenium cyclopentadienyl complex (RuPMC) was newly synthesized by a straightforward method. RuPMC was tested against human MCF7 and MDAMB231 breast and A2780 ovarian adenocarcinoma revealing IC50 values in the micromolar range. A pH dependent hydrolysis is advanced by preliminary UV-visible spectroscopy. Cellular distribution studies showed that RuPMC is predominantly found in the nucleus and in the membrane. Data suggest potential application of RuPMC as a new drug delivery system for Ru(II)Cp compounds.

Extrapolation techniques at short gauge lengths based on the weakest link concept for fibres exhibiting multiple failure modes

In order to extrapolate the tensile strength of fibres at short gauge lengths corresponding, for instance, to the mean fragment length in a fragmentation test or the so-called load-transfer length for unidirectional composite failure models, four types of extrapolation techniques have been reviewed. The ability of these models to describe the tensile strength of fibres is checked on E-glass fibres exhibiting multiple modes of failure. It is shown that Weibull unimodal statistics as well as the bimodal Weibull cumulative distribution function model lead to underestimated results. The double box approach provides values having a physical meaning but remaining phenomenological. The need for modelling to take a trimodality into account is emphasized.

Are microcomposites realistic models of the fibre/matrix interface? II. Physico-chemical approach

Abstract The physical and mechanical properties of microdroplets can differ significantly from those of the bulk material. This is especially true for epoxyde droplets, owing to (i) diffusion and vaporization of the hardener during the first step of the cure, (ii) surface oxidation and (iii) possible hydrolysis of the hardener during the first step of the cure schedule. The glass transition temperature of microdroplets was found to be 20–50°C lower than that of the bulk material. It is shown that this leads to microdroplets exhibiting a higher Youngs modulus and a lower yield point than the bulk network. Those discrepancies influence the adhesion between fibre and matrix by changing the stress distribution at the interface and can lead to biased results when comparing different matrices with the microbond test. The general idea that microbond specimens behave like ideal elastic components is now reassessed in view of (i) a plastic flow of the polymeric droplet and (ii) the occurrence of rate-dependent processes. This leads to a fundamental question regarding the use of microcomposites as a model of macroscopic-scale specimens.

Photoelastic studies of residual stresses around fillers embedded in an epoxy matrix

A photoelastic method was used to investigate the residual stresses in thermoset matrices during curing and cooling generated around spherical and high shape ratio fillers modelled by glass beads and glass or carbon fibers,respectively. Two types of reactive systems were selected: i/ based on a stoichiometric mixture of epoxy prepolymer and diamine comonomers -polycondensation-; ii/ based on a mixture of epoxy prepolymer and an anhydride -chain polymerization-. A mapping of the residual stresses was obtained after curing process and after hydrothermal aging. From such a method, the location of the maximal stresses and the extend of residual stresses field can be discussed as a function of the geometry of the inclusions, the nature of the matrix, and the aging. The photoelastic method can be effective for various types of fillers and polymer matrices in order to select the proper associations of components for composite materials.

On the significance and description of the size effect in multimodal fracture behavior. Experimental assessment on E-glass fibers

The existence of a size effect is an integral part of the physical phenomenon of brittle fracture. The literature dealing with the influence of fiber size on its ultimate strength has mainly focused on specimens whose failure is governed by a single category of flaw. In this work, we are discussing the size effect from a statistical point of view for fibers exhibiting multiple failure modes.