Polymers and Polymer Composites

Resin properties, such as heat deflection temperature (HDT) and tensile elongation, can affect composite lifetime under conditions of sustained stress at various temperatures in an aqueous environment. Measurement of time to failure of unidirectional glass fiber reinforced composite rods comprising E-glass fiber strands and one of a series of isopolyester resins suggests a correlation between stress, time to failure, and the temperature differential between the resin HDT and the exposure temperature. Time to failure decreases significantly at moderate relative stress as the temperature differential (HDT – exposure temperature) becomes less than 10 °C.

This paper presents the results of an investigation on the buckling behavior of concentrically loaded thin–walled pultruded fiber reinforced polymer (PFRP) composite columns. Both open- and closed-web columns were evaluated. Finite element (FE) analysis and theoretical predictions are presented and correlated with experimental data. Good agreement between theoretical, analytical and experimental results was achieved. The paper also presents design guidelines to determine the bending stiffness and the critical buckling load for pultruded composite columns. In addition, a discussion on the axial strength of unidirectional PFRP columns and identification of different modes of failure are presented.

This study was an attempt to answer the question, “How many monomer repeat units are necessary in molecular dynamics simulation in order to obtain reliable (i.e. repeatable) solutions?” A series of numerical tests was conducted to provide an answer. Based on the numerical results, reliable solutions required approximately ten thousand monomer repeat units at minimum, which was the sum of the monomer units in every polymer chain molecule. It did not matter much whether there were longer chain polymer molecules in a small quantity or shorter chain polymer molecules in a large quantity. What was critical was the total number of monomer repeat units. For a particle reinforced composite that consists of metallic atoms embedded in a polymer matrix, the minimum number of total monomer repeat units in the polymer matrix was approximately five thousand for reliable solutions.

The present paper describes a feasible process to reuse glass fibres separated from phenolic prepreg waste as reinforcing filler in polypropylene (PP) and polyamide 6 (PA6). Prior to compounding, the recovered glass fibres were cut into 50 mm long fibre bundles and surface treated with gamma-aminopropyltriethoxysilane (APS) for increased composite interfacial strength. Electron Spectroscopy for Chemical Analysis (ESCA) and Atomic Force Microscopy (AFM) showed that the silane coupling agent was attached to the surface of the glass fibres but the silane layer was somewhat uneven, probably due to the presence of small amounts of organic contaminants. In addition it was found necessary to clean the glass fibres from organic contaminants by thermal treatment in order to attach silane coupling agent to the surfaces. The tensile strengths obtained for PP and PA6 composites with 30 wt% filler level of surface treated recovered glass fibres were 49 MPa and 101 MPa, respectively. This should be compared to 30 MPa and 75 MPa for composites containing untreated glass fibres and 19 MPa and 52 MPa for pure PP and PA6. Addition of 5 wt% PP-g-MA compatibiliser to the PP composite increased the tensile strength by another 14%, i.e. to 56 MPa. The good interfacial compatibility achieved by APS surface treatment and compatibilisation was verified by Scanning Electron Microscopy (SEM).

Phenolic resin impregnated glass-fibre prepreg waste was milled and used as reinforcing filler in polypropylene (PP) and polyamide 6 (PA6). Prepreg was particularly suitable to be used as filler in PA6. The fibres were homogeneously distributed during compounding and the addition of 20 wt% prepreg increased the tensile strength of PA6 by 63%, from 52 MPa to 85 MPa. Milled prepreg alone did not significantly increase the tensile strength of PP. However, if compounded together with maleic anhydride grafted polypropylene (PP-g-MA, Epolene G3003) compatibiliser, prepreg can be used as reinforcing filler in PP as well. Addition of 20 wt% prepreg together with 5 wt% Epolene G3003 increased the tensile strength of PP from 26 MPa to 43 MPa.

In order to mill the prepreg for compounding with thermoplastics it has to be cured. A 2 kg batch of prepreg had to be cured for at least 2 hours at 200 °C to prevent the phenolic resin from falling off the glass-fibres. Milling should be performed using screens with holes larger than 3 mm in diameter to reduce the amount of prepreg fibres shorter than 2 mm, as they jam the hopper when feeding the recyclate to the extruder. The initial prepreg fibre length is of little importance to the composite mechanical properties, as the fibres are shortened to approximately the same length during compounding.

This paper discusses the stabilisation of three-dimensional woven carbon fibre preforms. A polyethylene monofilament has been incorporated within the structure during weaving and, by the application of temperature and pressure, it has been used to consolidate the edges of carbon fibre preforms. Upon testing the plastic was found to have had a positive effect on maintaining the stability of the preform. Impregnation of modified preforms was undertaken by Resin Transfer Moulding (RTM) in order to assess mechanical properties. The properties of composites specifically made from modified preforms were comparable with those of a conventional composite.

Novel unsaturated poly (ester-amide) resins (UPEAs) were prepared by the reaction between an epoxy resin, namely diglycidyl ether of bisphenol–A (DGEBA) and unsaturated aliphatic bisamic acids, using a base catalyst. These UPEAs were then blended with a vinyl monomer namely, methyl methacrylate (MMA) to produce a homogeneous resin syrup. The curing of these UPEAs-MMA resin blends was carried out by using benzoyl peroxide (BPO) as a catalyst and was monitored by using a differential scanning calorimeter (DSC). The glass fibre reinforced composites (i.e. laminates) of this UPEA-MMA resin blends were fabricated using the DSC data. The chemical, mechanical and electrical properties of the glass fibre composites have also been evaluated. The unreinforced cured samples of the UPEA-MMA resin blends were also analysed by thermogravimetry (TGA).

The influence of γ-irradiation on the electrical, swelling and mechanical properties of cross- linked butyl (IIR) rubber and ethylene propylene diene monomer (EPDM) and their blends have been investigated. The modulus increased, while the elongation at break decreased with irradiation. The gap width between carbon-carbon particles is found to be highly affected by the irradiation dose, which in turns influenced the electrical conductivity of these blends. The swelling equilibrium data in different solvents were analyzed by the Flory-Rehner equation to obtain estimates of the average molecular weight and cross-link density.