Structure-property relationships in structural glass fibre reinforced composites from unsaturated polyester and inherently fire retardant phenolic resin matrix blends

The effects of matrices from co-cured blends of an unsaturated polyester (UP) with inherently fire-retardant and char-forming phenolic resoles (PH) on the mechanical and fire performances of resultant glass fibre-reinforced composites have been investigated. Three different phenolic resoles with increasing order of compatibility with UP have been used. These are: (i) an ethanol soluble resin, (PH-S), (ii) an epoxy-functionalized resin (PH-Ep), and (iii) an allyl-functionalized resin (PH-Al). The mechanical properties of the composites increased with increasing compatibility with two resin types as might be expected, but not previously demonstrated. However, even with the least compatible resin (PH-S), the impact properties were unaffected and the flexural/tensile properties while reduced, were still acceptable for certain applications. Fire properties were however, in reverse order as previously observed in cast resin samples from these composites. Moreover, the reduction in flammability was less compared to those of the cast resin samples, reported previously, explained here based on the insulating effect of glass fibre reinforcement

Thermo-mechanical responses of fiber-reinforced epoxy composites exposed to high temperature environments. Part I: experimental data acquisition

This first part of a series of papers on the thermo-mechanical responses of fiber-reinforced composites at elevated temperatures reports the experimental results required as input data in order to validate the kinetic, heat transfer, and thermo-mechanical models being developed and to be discussed in subsequent papers. Here the experimental techniques used for the determination of physical, thermal, and mechanical properties and their significance for particular models are discussed. The fire retardant system used to improve the fire performance of glass fiber-reinforced epoxy composites is a combination of a cellulosic charring agent and an interactive intumescent, melamine phosphate. Thermogravimetry is used to obtain kinetic parameters and to evaluate the temperature-dependent physical properties such as density, thermal conductivity, and specific heat capacity, determined using other techniques. During flammability evaluation under a cone calorimeter at 50 kW/m2 heat flux, thermocouples are used to measure temperatures through the thicknesses of samples. To investigate their thermo-mechanical behavior, the composites are exposed to different heating environments and their residual flexural modulus after cooling to ambient temperatures determined. At a low heating rate of 10°C/min and convective conditions, there was a minimal effect of fire retardant additives on mechanical property retention, indicating that fire retardants have no effect on the glass transition temperature of the resin. On the other hand, the fireretarded coupons exposed to a radiant heat from cone calorimeter, where the heating rate is about 200C/min, showed 60% retention of flexural modulus after a 40-s exposure, compared to 20% retention observed for the control sample after cooling specimens to ambient temperatures

Quantification of polymer degradation during melt dripping of thermoplastic polymers

This work reports measurement of temperatures of the melting drops in the previously designed and presented melt dripping experiments of thermoplastic polymers. A simple heat transfer model has been used to compute the surface temperatures of the polymer sample at various furnace temperatures and thus the temperatures of the molten drops dripping from the melting surface. The model has been validated by experimental results. The temperatures of the molten drops could help in predicting the degree of degradation in a polymer during melt dripping. By conducting thermogravimetric analysis of both the polymers and their molten drops, a degree of degradation could also be predicted. The values obtained from both approaches have been compared in order to understand the melt dripping/degradation behaviour of polymer

The potential of metal oxalates as novel flame retardants and synergists for engineering polymers

Based on their known decomposition to carbon dioxide, carbon monoxide and the respective oxide, six metal (calcium, manganese (II), iron (II), copper (II), tin (II) and zinc) were synthesised and assessed for their potential flame retardant activity in the absence and presence of selected flame retardants. Initially they were assessed when impregnated on cotton as a screening process and then selectively compounded with polyamide 6.6 (PA66), as a typical engineering polymer. Only manganese (II) and iron (II) oxalates alone reduced the burning rate of cotton, whereas together with ammonium bromide, calcium and iron (II) oxalates showed an apparent additional burning rate reducing effect. Derived synergistic effectivity (Es) values fall within the limits 0<Es<1 indicating a less than additive interaction. TGA/DTA analysis of oxalate/PA66 blends suggested that only zinc oxalate (ZnOx) offers both possible flame retardant activity in terms of enhanced residue formation ≥500oC, coupled with acceptable stability in molten PA66. When compounded with PA66, in the presence and absence of either aluminium diethyl phosphinate (AlPi)-based or selected polymeric bromine-containing flame retardants, LOI values increased in most PA66/ZnOx/flame retardant blends but UL94 test ratings were disappointingly low and more likely than not, “fails”. PA66/ZnOx blends with AlPi and AlPi/MPP gave poor plaques suggesting that thermal interactions were occurring during compounding. The bromine-containing blends had better processibility and both TGA and cone calorimetric studies showed that the PA66/poly(bromopentabromobenzyl acrylate)/ZnOx sample not only yielded the highest residues in air and nitrogen at 500 and 580oC, but also the lowest peak heat release rate value of 398 compared with 1276 kW/m2 for pure PA66. The derived Es value for this blend is 1.17 suggesting a small level of synergy between the zinc oxalate and poly(pentabromobenzyl acrylate) flame retardant. The possible role of zinc bromide is discussed