ABSTRACT

The evaluation of Hot-Gas and Heated-Tool weldments of Polypropylene/Bone composite was conducted. The composites were formulated by incorporating up to 30% by weight of calcined cow bone powder at an interval of 5% and -75μmsieved size was used as reinforcing phase during compounding process. The polypropylene materials (in unreinforced state) and various polypropylene/bone composites were welded, using hot-gas and heated-tool welding processes. Mechanical properties (tensile strength, flexural strength, impact strength and hardness) and physical properties (density, water absorption, degradability and morphology) of polypropylene and polypropylene/bone composite in both unwelded and welded conditions were examined. Results obtained showed increase in density (by 40% at 30% reinforcement); the amount of water absorbed increased as the time of immersion increased. Although the unreinforced polypropylene was saturated after 192 hrs of immersion in water, the reinforced composite’s water uptake continued beyond 192 hrs in proportion of filler amount. Similarly, there were marked improvements in mechanical properties in the Unwelded Composite (UWC), which was attributed to the reinforcing ability of the bone. However, relatively lower values were recorded when welded samples were examined. More so, there were drops in tensile strength after 15% (40.91MPa) and 20% (41.54 MPa) in Heated Tool Weldments (HTW) and Hot Gas Weldments (HGW) respectively. On the basis of comparison, these values showed that at 15% reinforcement addition, HTW has strength value 16.70% lower than UWC of the same composition (15% bone), while in composite with 20% of reinforcement, the strength value of HGW was found to be 23.23% lower than UWC of the same composition. Furthermore, flexural strength and hardness witnessed increase as more of polypropylene was replaced by bone powder. Impact energy decreased and then increased; after 10% of reinforcement addition, all but UWC set of samples witnessed drop in their ability to absorb energy on impact as a result of bone additions. These behaviours have been explained in terms of strengthening effect and volume fraction of the reinforcement as well as the effect of welding processes.

INTRODUCTION

The development of many technologies that make our existence so comfortable depends largely on the availability of suitable materials (Callister, 2007). However, most of these technologies require a material with unusual combination of properties (e.g. high specific strength, magnetic–transparent, conductive–transparent, catalytic–magnetic, huge yet invisible to human eye and so on), which indeed exceed the domain of our conventional metal alloys, ceramics, polymers, heat treatments etc (Luigi and Gianfranco, 2005;Hanemann and Vinga 2010).Nevertheless, the use of compositesas another class of engineering materials has proven to be vital and a promising candidate in the areas of these advanced technologies. Other answers to these contemporary developments include bio-technology, nanotechnology to mention a few. Composites were developed to improve on the properties (strength to weight ratio, good corrosion resistance, thermal stability etc) of a monolithic material so that it could be used in sophisticated areas such as aviation (where high specific strength is desired), marine (where low weight and high corrosion resistance guaranty safety), sporting equipment (where less weight is appreciated), and many other applications which include high performance rocket-motor and pressure vessels (Harris, 1999). Composites are made up of primarily two major individual materials referred to as constituent materials. These constituent materials are termed as matrix and reinforcement. At least one portion of each type is required. The matrix material surrounds and supports the reinforcement materials by maintaining their relative positions; while the reinforcements impart their special mechanical and physical properties to enhance the matrix properties. The net effect is thus an attainment of a material with a unique combination of properties not common to either the matrix or the reinforcement (Matthews and Rawlings, 2005; Callister 2007). The common matrices used include metals/alloys, ceramics and polymers while the reinforcement can be in form of fibre (short or continuous) or particulate reinforcement (Hull and Clyne, 1981).

Depending on the matrix and the reinforcement used in composite formulation, properties of the composite are indeed direct interpolation of its constituents’ properties. As a consequence,thermoplastic composites display appreciable properties which are known to be inherent features of their matrices (Matthews and Rawlings, 2005). In line with this, thermoplastic reinforced composites enjoy high demand with increased interest to developing technologies that transform these classes of composites into a form most suitable for practical applications (Yousefpour et al., 2004).