The compounding of short fibre reinforced thermoplastic composites

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.It is generally accepted that the mechanical properties of short fibre reinforced thermoplastics do not correspond with the high mechanical properties of fibres used to reinforce them. A study is made into the methods of compounding reinforcing fibres into thermoplastics to produce short fibre reinforced thermoplastics of enhanced properties. The initial method chosen for investigation is the twin screw extrusion compounding process. Variables such as fibre feeding arrangement and extrusion screw design are found to be factors influencing the properties of carbon and glass reinforced nylon 6,6. Use is made of computer programs to predict properties, assess compound quality and estimate fibre-matrix bond strength. Investigations indicate that the presence of reinforcing fibres with enhanced lengths does not result in the predicted property increases. The reasons for this shortfall are believed to lie in unfavourable fibre orientation in injection mouldings and the reduced strain to break of these materials. Short Kevlar reinforced thermoplastics are compounded and their mechanical properties assessed. The reasons for the poor mechanical properties for these materials are identified as a poor bond strength between fibre and matrix, the formation of points of weakness within the fibres by the compounding and moulding processes and the coiled arrangement of fibres present in injection mouldings. A method suitable for the routine assessment of fibre-matrix bond strength is used to examine combinations of fibre and thermoplastic matrix. A comparison is made of the values derived from this method with values calculated from stress-strain curves of injection mouldings. This allows an understanding of the nature of the fibre-matrix bond yielded by compounding and injection moulding steps. A description is given of a novel method designed to overcome the limitations of conventional compounding routes to produce long fibre reinforced injection moulding feedstock. Further work is necessary before this method is a feasible production technique

Socioeconomic status and smoking: A review

Smoking prevalence is higher among disadvantaged groups, and disadvantaged smokers may face higher exposure to tobacco's harms. Uptake may also be higher among those with low socioeconomic status (SES), and quit attempts are less likely to be successful. Studies have suggested that this may be the result of reduced social support for quitting, low motivation to quit, stronger addiction to tobacco, increased likelihood of not completing courses of pharmacotherapy or behavioral support sessions, psychological differences such as lack of self-efficacy, and tobacco industry marketing. Evidence of interventions that work among lower socioeconomic groups is sparse. Raising the price of tobacco products appears to be the tobacco control intervention with the most potential to reduce health inequalities from tobacco. Targeted cessation programs and mass media interventions can also contribute to reducing inequalities. To tackle the high prevalence of smoking among disadvantaged groups, a combination of tobacco control measures is required, and these should be delivered in conjunction with wider attempts to address inequalities in health