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Polymers and Polymer Composites

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Title: PREFORM TECHNOLOGY: A NECESSARY REQUIREMENT FOR QUALITY CONTROLLED LCM-PROCESSES
Page Range: p.605-622
Author(s): Mitschang P; Ogale A; Schlimbach J; Weyrauch F; Weimer C
File size: 749K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 11
Issue No: No. 8

Abstract
This article discusses the need to use preform techniques to produce qualified and manageable reinforcements as a requirement for further steps in the development of liquid composite moulding (LCM) processes. The definition and philosophy of the 'sew 'n' cut' technique based on tailored reinforcements shows an alternative to direct preform technologies. The importance of selecting adequate thread construction and properties, such as elastic behaviour in order to minimise the influence on ellipse generation and the in-plane properties of the reinforcement are examined. Based on such performs, the control of the LCM process is shown to be possible. Different concepts to realise a controlled injection are discussed,and the decision-tree-concept is described in detail and verified by controlling the race-tracking effect. A critical preforming effort is defined whereby a further increase in preforming activities will nullify the expected cost advantages. 59 refs.

Title: EFFECTS OF STYRENE EVAPORATION ON THE CURE KINETICS BEHAVIOUR OF A VINYLESTER RESIN SYSTEM SUITABLE FOR COMPOSITE PULTRUSION
Page Range: p.623-632
Author(s): Samaras Z I; Partridge I K
File size: 130K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 11
Issue No: No. 8

Abstract
An experimental and modelling methodology is described, by which the effects of styrene evaporation on the cure kinetics and the conversion evolution in a vinylester resin is studied and quantified. Under the particular geometry and environmental conditions used in the experiments, styrene losses up to 6% of the initial styrene concentration per day are observed.. The complex curing reaction was modelled with empirical equations, and the overall curing mechanism was found to be unaffected by the styrene evaporation. The maximum reduction in the final Tg of a fully cured sample was found to be 3 degrees C, for styrene losses of over 25% of the original amount, and is therefore not considered to be of significant concern in the pultrusion process with this vinylester resin. The exothermicity of the reaction, however, was significantly affected by the reduction in styrene content. Practical solutions for preventing this are suggested. 22 refs.

Title: COUPLED HYGROTHERMAL COHESIVE-LAYER CONSTITUTIVE MODEL FOR SIMULATING DEBOND GROWTH
Page Range: p.633-648
Author(s): Roy S; Shiue F-W
File size: 196K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 11
Issue No: No. 8

Abstract
In order to model the synergistic bond degradation mechanisms that may occur at the interface between a fibre-reinforced polymer and concrete, a two-dimensional cohesive layer constitutive model with a prescribed traction-separation law was constructed. It was formulated using the basic principles of continuum mechanics and thermodynamics, taking into account concentration-dependent and strain-dependent non-Fickian hygrothermal effects that are likely to occur within a cohesive layer. Implementation of the model in a test-bed finite element code was carried out and code verification was performed. Benchmark comparisons of finite element prediction of critical load with analytical results for a double cantilever beam specimen were shown to be in good agreement. Numerical simulation of a wedge-test involving debond growth caused by synergistic interaction between local stress and diffusing moisture was also presented to demonstrate the ability of the cohesive layer model to simulate environmental cracking. 13 refs.

Title: DIPSERSIBILITY OF MACROMOLECULAR POLYOLS AS CO-STABILIZER IN POLY(VINYL CHLORIDE) AND THEIR STABILIZATION EFFECT COMBINED WITH SYNERGETIC METAL SOAP
Page Range: p.649-662
Author(s): Ikeda H; Ishikawa M; Nakamura Y; Iida T
File size: 200K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 11
Issue No: No. 8

Abstract
An investigation is reported into the use of heat stabilisers for PVC in order to prevent discolouration on heating. The synergistic effect of polyvinyl alcohol (PVA) as co-stabiliser with a mixture of zinc and calcium stearates is discussed. When the PVA and PVC were pre-mixed in the powder state, the compound obtained showed a lower stabilisation effect on the discolouration of PVC, whereas when a PVA aqueous solution was prepared and the PVC powder was added to the PVA solution and dried, the resulting compound showed a superior stabilisation effect. The dispersed PVA domain size in the PVC sheets was measured quantitatively by image processing analysis, using the optical micrographs of the sheets. It was found that there was a good relationship between the dispersibility of PVA and its stabilisation effect. Thus, the co-stabilising effect of PVA increased with a decrease in the domain size. This was also confirmed by using different polyols as co-stabilisers. 11 refs.

Title: MELT VISCOELASTICITY OF POLYAMIDE 6 ORGANOCLAY NANOCOMPOSITES
Page Range: p.663-668
Author(s): Karaman V M; Shumsky V F; Privalko E G; Privalko V P; Lehmann B; Friedrich K
File size: 70K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 11
Issue No: No. 8

Abstract
Thermoplastics reinforced with relatively small amounts of organoclay particles are particularly useful as engineering materials. However, their processability has been found to present some problems with respect to the extreme sensitivity of melt flow behaviour to the aspect ratio of clay nanoparticles and to the quality of their dispersion. In addition, viscoelastic studies of irradiation-grafted nano-inorganic particle-filled PP composites in the melt state, revealed the onset of a plastic yield phenomenon for a nanocomposite with the filler volume content as low as 4.68%. This study focuses on commercial nanocomposites of nylon-6 which were prepared by melt compounding with organoclay hybrids, and which were subsequently characterised by complex viscosities and relaxation time spectra derived from storage and shear loss modulus. Results were rationalised in terms of (P1)model considerations. At the lowest clay loading (2.5%), the Newtonian viscosity suggested a lower equilibrium elasticity modulus of an entangled melt, as if the organoclay particles had acted as specific 'diluents' for the initial entanglement network. At increased clay contents, this effect was taken over the growing importance of strong interactions at the nanoparticle/melt interface, leading to the formation of a fairly thick boundary interphase (BI) around the nanoparticles, and eventually, resulting in a build-up of an 'indefinite cluster' of clay nanoparticles coated with BI at the highest clay loading (7.5%). 17 refs.

Title: MODELLING ORTHOTROPIC VISCOELASTIC BEHAVIOUR OF COMPOSITE LAMINATES USING A COINCIDENT ELEMENT METHOD
Page Range: p.669-677
Author(s): Nallainathan L; Liu X L; Chiu W K; Jones R
File size: 145K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 11
Issue No: No. 8

Abstract
This paper presents a finite element procedure for modelling the viscoelastic behaviour of orthotropic composites. The procedure uses a commercially available finite element package known as ABAQUS and requires no code development. Consequently, the procedure is claimed to be highly flexible and has the potential to be applied to a wide range of practical problems. ABAQUS is a general-purpose package for structural and non-structural analyses, but the orthotropic behaviour of laminated composites that can be modelled by ABAQUS is restricted to circumstances involving simple elasticity and plasticity, not viscoelasticity. However, it is known that the viscoelasticity in laminated polymer composites is significantly orthotropic, and so to overcome this limitation of the FEA package, a simple procedure is proposed and described, which is referred to as the Coincident Element Method (CEM). In this method, a composite method is modelled by using two shell elements which are superimposed onto each other in such a way that they are coincident, i.e., the two shell elements share the same nodes and deform together. Numerical examples are presented to illustrate the capacity and accuracy of the procedure. 9 refs.

Title: PHOTOPHYSICS AND APPLICATIONS IN PLASTIC SOLAR CELLS OF CONJUGATED POLYMER/FULLERENE COMPOSITES
Page Range: p.679-689
Author(s): Lin H; Huang H; Qingguo H; Bai F
File size: 132K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 11
Issue No: No. 8

Abstract
Two types of conjugated polymer were synthesised for application in solar cells. One type was a linear conjugated alternating copolymer containing hole-transporting groups (e.g. triphenylamine and N-substituted carbazole) in the backbone, and the other was a PPV-based hyperbranched conjugated polymer. The composites of these polymers with fullerene were investigated, with particular reference to the photoinduced electron transfer and other related photophysical processes occurring in the composites. Strong fluorescence quenching of these conjugated polymers on mixing them with C60 in dilute solution. Anion radical species of C60 were observed in ESR measurements as a result of photoinduced charge separation. The quenching constants vary with different conjugated polymers, and thus provide a quantum measurement for the interaction between the donor and acceptor. An energy conversion efficiency of up to 1.1% is reported for solar cells manufactured from conjugated polymer/fullerene composites. 17 refs.

Title: INTUMESCENT PP BLENDS
Page Range: p.691-702
Author(s): Almeras X; Le Bras M; Bourbigot S; Hornsby P; Marosi G; Anna P; Poutch F
File size: 111K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 11
Issue No: No. 8

Abstract
This work reports research carried out to develop an intumescent blend for transport applications, which would provide good fire and mechanical performance, and which would comply with recent European directives on the recycling of end-of-life cars. The study shows that PP/APP/PA6 based intumescent blends in which EVA copolymers were used as compatibilisers, with the addition of talc, are able to provide acceptable mechanical properties without decreasing flame retardancy. 42 refs.

Title: HEAT-RESISTANT ORGANIC MATRICES QUO VADIS? (REVIEW)
Page Range: p.703-728
Author(s): Romdhane H B; Sillion B; Grenier-Loustalot M F
File size: 300K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 11
Issue No: No. 8

Abstract
A review is presented of the characteristics required for heat resistant composite matrices, with details of two possible approaches based on linear polymers and telechelic oligomers that can be crosslinked during use. Special attention is given to crosslinkable oligomers. The different structures studied are bismaleimides, bismaleimides modified by cyanates or epoxies, bisnadimides, acetylene and propargylic compounds. These are discussed in terms of chemistry (stability of oligomers, mode of polymerisation, ageing), and ductility. A discussion is presented of several little used solutions, i.e., semi-interpenetrated networks, molecular composites, polymerisable molecular assemblies, hyper-branched oligomers and liquid crystal monomers, etc., with reference to their future relevance. Despite the fact that technical solutions may be found for use of such materials up to 300 degrees C, the market is considered to be too small for these products to be further developed. 75 refs.

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