Peter R. Hornsby

Preparation and properties of polypropylene composites reinforced with wheat and flax straw fibres: Part II Analysis of composite microstructure and mechanical properties

The microstructure and mechanical properties of polypropylene composites containing flax and wheat straw fibres are discussed. Particular emphasis has been given to determining the nature and consequences of fibre damage induced during melt-processing operations, fibre orientation occurring in mouldings, and possible interfacial adhesion between the matrix and fibres. Compared to unfilled polypropylene, addition of flax and wheat straw caused a significant increase in tensile modulus, particularly, in the case of flax fibres, which also gave higher tensile yield strength and Charpy toughness, despite a lack of interfacial bonding. Tensile strength was increased further through inclusion of 5% by weight of maleic anhydride-modified polypropylene, which was shown to promote adhesion between fibres and matrix.

Effect of fillers on the fire retardancy of intumescent polypropylene compounds

Abstract The effects of fillers (talc and calcium carbonate) were investigated on polypropylene /ammonium polyphosphate/polyamide-6 (PP/APP/PA-6) intumescent system by using mechanical testing, LOI method, cone calorimetry and thermoanalytical techniques. Calcium carbonate and talc affect the fire protective properties of PP/APP/PA-6 system in different ways. It is shown that talc induces an increase in the Youngs modulus and a decrease in the elongation at break. Calcium carbonate leads to a decrease in the elongation at break, but there is no improvement in the Youngs modulus. Talc increases fire protective performance due to forming a ceramic like protective shield at the surface, whereas calcium carbonate decreases it because of a reaction with APP. Effects of talc and calcium carbonate were furthermore investigated on PP/APP/PA-6 system by measuring Rate of Heat Release (RHR), Total Heat Emitted (THE), CO/CO 2 evolution and residual mass. Results are interpreted by means of decomposition, chemical reaction between components and formation of a protective shield at the surface at ignition.

Preparation and properties of polypropylene composites reinforced with wheat and flax straw fibres. Part I : Fibre characterization

The microstructure, thermal and mechanical properties of flax and wheat straw fibres have been examined with a view to using these natural fibres as reinforcing additives for thermoplastics. In this regard, the fibres were characterized prior to incorporation into the polymer, using a range of techniques, including SEM, image analysis, thermogravimetric analysis and micro-mechanical tensile testing, at room and elevated temperatures. The thermal and mechanical properties obtained have been discussed in relation to the measured composition and structural form of the fibres.

Effects of tin additives on the flammability and smoke emission characteristics of halogen-free ethylene-vinyl acetate copolymer

Abstract Zinc hydroxystannate (ZHS) is found to be an effective partial replacement for the conventional hydrated fire-retardant fillers alumina trihydrate (ATH) and magnesium hydroxide (MH) when incorporated into a halogen-free EVA cable compound. In contrast to earlier findings for halogen-containing polymers, ZHS-coated versions of the fillers are somewhat less effective than equivalent composition mixtures of ZHS+filler. Incorporation of ZHS also greatly enhances the performance of an ATH/nano-clay synergistic fire-retardant system in the EVA formulation and allows marked reductions to be made in overall filler level with no or little compromise in terms of flame-retardant and smoke-suppressant properties.

Interfacial modification of polypropylene composites filled with magnesium hydroxide

The mechanical behaviour of polypropylene composites containing magnesium hydroxide is considered with reference to the influence on properties of filler surface modification. Compared to composites containing untreated filler, mechanical properties can be strongly affected by the chemical nature and amount of surface treatment applied. In particular, very significant improvements in toughness are obtained using sufficiently high levels of magnesium stearate to ensure complete coverage of the magnesium hydroxide surface. Results are discussed in terms of the observed deformation mechanism in the polymer matrix.

Zinc hydroxystannate-coated metal hydroxide fire retardants: Fire performance and substrate-coating interactions

Fire retardant (FR) properties, including limiting oxygen index, peak rate of heat release and smoke parameter have been measured and compared for unfilled and filled polyvinyl-chloride (PVC) based cable formulations, containing various amounts of uncoated and zinc-hydroxystannate (ZHS)-coated alumina trihydrate (ATH) and magnesium hydroxide (MH) fillers. Uncoated ATH or MH proved to be efficient FR additives, but when coated with ZHS, further improvements were observed. ATH was more effective than MH in both uncoated and ZHS-coated forms. For a halogen-free ethylene-vinyl acetate (EVA) cable formulation, the content of vinyl acetate and loading of ZHS-coated ATH required to yield optimum FR properties was determined. The interaction between ATH substrate and ZHS coating was also studied by X-ray photoelectron spectroscopy and diffuse reflectance infrared Fourier-transform spectroscopy, using samples with ZHS-contents ranging from 1 to 15 wt%. An increase in the binding energies of the Zn 2p3/2 and Sn 3d5/2 peaks was found, together with alterations in the positions of the (Sn)O—H stretching bands. There was no evidence for condensation and the formation of Al—O—Sn bonds.

Rheological characterization of polypropylene filled with magnesium hydroxide

Consideration is given to the dynamic viscoelastic and shear flow properties of magnesium hydroxide-filled polypropylene, at a filler concentration of 60 wt%. Five variants of magnesium hydroxide were used, one surface-treated with magnesium stearate. The results reported illustrate the effects of filler particle size, morphology and surface coating on the rheology of the composites. The presence of magnesium hydroxide caused a significant increase in the shear viscosity of polypropylene relative to unfilled polymer, although this was much less pronounced using surface-treated filler, particularly at low shear rates. Complex viscosity and storage modulus data, obtained at very low shear rates (0.002 s−1), demonstrated the presence of a critical shear yield stress for flow to occur, which was greatest for compositions containing uncoated fillers with small particle size. These observations are discussed in terms of structure formation between the particles. Results obtained from capillary and dynamic measurements of melt flow were found to follow the Cox-Merz rule.

Fracture toughness of multiphase polypropylene composites containing rubbery and particulate inclusions

The fracture toughness of binary and ternary phase polypropylene (PP) composites containing ethylene–propylene rubber (EPR) and glass beads, has been studied using the J-integral method at 23 and − 20 °C. For determining Jc, analysis of the stress-whitening zone was found to be more meaningful than the commonly used blunting line approach. Functionalized EPR was found to be more effective toughening additive for PP than EPR, in both binary and ternary phase compositions. Crack growth mechanisms were examined by scanning electron microscopy. In rubber-modified blends, cavitation and shear yielding were found to be the primary toughening mechanisms, while in ternary phase composites particle–matrix debonding played a major role.

Mechanism of sintering between polypropylene beads

Using experimental results obtained by hot-stage light microscopy, the sintering behaviour of off-reactor spherical grades of polypropylene and poly(methyl methacrylate) were considered. Sintering rates were found to be strongly influenced by initial particle size, melt temperature and viscosity and could be modelled using the Frenkel equation. Examination of the microstructure between sintered polypropylene particles revealed a distinct transcrystalline zone, which was relatively insensitive to sintering temperature and cooling rate.

Comminuted thermoset recyclate as a reinforcing filler for thermoplastics Part I Characterisation of recyclate feedstocks

This, and a subsequent paper consider the re-use of thermoset recyclate as a functional filler for polypropylene. Emphasis is given in this communication to characterisation of feedstocks produced by size-reducing dough moulding compound (DMC) and woven glass phenolic laminate (GWP). The physical properties of these microcomposite particulates have been analysed to determine their size, morphology, structural integrity and thermal stability at polypropylene melt processing temperatures. The DMC recyclate was found to have a glass fibre content of 26w/o, with fibres up to 10 mm retained in the comminuted particulates. The material is stable up to ∼220°C. The GWP, however comprised 79w/o of woven glass platelets which are largely preserved in the size-reduced recyclate. The material is thermally stable up to 290°C.