After 1000 hours of exposure to UV radiation plus condensation, the composites lost almost 30% of their intrinsic tensile modulus. The reduction in tensile modulus is more gradual for composites exposed to UV radiation only. After 1000 hours of exposure to UV radiation, the composites lost approximately 30% of their intrinsic modulus. However the loss in modulus is less for composites exposed to UV and UV plus condensation conditions compared to immersion in water. This is to be expected since the diffusion of water into the composites affects the bulk properties of the material, plasticising the polyester matrix and fibres. UV and condensation mostly affect the surface properties of the material only, thus having less effect on bulk properties of the material.Hence the greater reduction in modulus for composites immersed in water.
The effect of UV radiation and condensation on strain to failure of the composites is shown in Figure 6. The strain to failure does not seem to have been affected very much by exposure to these conditions and stays close to the non-exposed value of 1%. However the strain to failure of composites immersed in water is considerably higher which can again be explained by the fact that the diffusion of water results in plasticisation of polyesterresin and fibres, resulting in increase in strain to failure. UV and condensation affect the surface properties and hence the strain to failure is not affected.The exposure of composites to UV and condensation did not affect their fracture mode which was completely brittle as for non-exposed composites which was in agreement with the similar strain to failure values for both cases. Figure 7 shows the comparison of stress-strain graphs of composites following exposure to both kinds of environments for 1000 hours with unexposed and water-immersed composites. The figure shows that the mechanical behaviour of the composites following exposure to weathering conditions did not change and the shape of the curve was found to be similar to that for unexposed composites, with a “knee” forming on the curve which is a characteristic of short fibre composites. One notable effect these conditions had was on the colour of these composites.
The UV light can result in considerable yellowing of synthetic fibre composites also. The colour of these composites started to change from darkish brown to greyish brown. After 1000 hours of exposure it had changed to whitish brown as shown in Figure 8 and Figure 8. In each case, the top figure shows the hemp fibre sample without exposure to weathering conditions. The reaction of water, oxygen and UV radiation within the organic matter in the composite spromote the change of colour. Mehta et al.studied the effect of accelerated weathering on colour change of natural fibre reinforced polyester composites by using reflectometer.The composites changed colour from greenish brown to white and the change in colour was more pronounced for hemp fibre composites than flax and big blue stem grass composites. Hence the interaction of hemp fibres with UV light and water can be considered to be the main reason for change in colour.It has also been shown that the exposure of polyester to accelerated outdoor weathering can result in change in its colour, measured by yellowness index. Thus both polyester resin and hemp fibres are expected to contribute to yellowness of the material. The discolouring and yellowness of the surface was more pronounced for composites exposed to UV radiation plus condensation because the moisture also contributed to the discolouring,which was also observed for composites immersed in distilled water.
This fading of colour can have important aesthetic implications when these composites are to be used in outdoor applications. Some sort of coating, paint or UV absorbing additives can be used on these composites to stop the fading effect. The exponential desire to legalize Cannabis sativa in many countries is an interesting observation that cannot be underestimated. The proponents pushing for the legalization of this drug may have genuine concerns but authorities in government must ensure the drug is prescribed by a competent medical practioner.The grave effects of its unregulated use may outweigh its benefits. Nonetheless,responsible use of this drug may save lives because of its known potency against viral diseases. Generally, Marijuana is the second most widely and illegally abused drug substance across the world after tobacco. This mainly because of the psychoactive effects induced by delta-9-tetra hydrocannabinol chemical,indicated as 1 in Figure 1, which is obtained from dried leaves, stems, seeds and flowers of the Cannabis sativa hemp plant .