Discussion of Tensile Strength Reults

The additions of fibres to the cellulose acetate actually weakened the material. A possible reason that our reinforced samples performed worse than the control samples might be again due to the air bubble problem. The cellulose acetate mixture tended to stick to the fibres, but because there was not enough force to compress the fibres tightly together, air pockets formed as the mixture dried. Commercial production of plastic products would use a compression moulding machine, where great force is applied to the plastic as it dries, eliminating the problem of air pockets. We were unable to obtain a compression moulder to make our samples, but if we had, the results would likely have been more promising. As well, we used very short fibres, and had we used unidirectional long fibres, the results might have been better.

As well, our first tensile strength test showed that the fibre reinforced samples were much stronger than the control samples. For the first experiment, both the control sample and the reinforcement samples experienced problems with air pockets, and because the air bubbles were generally uniform for all of the samples, we were able to compare the control and the reinforced samples side by side.

For this experiment, out of all the fibre reinforced samples, the 5% hair sample was the strongest, with an average ultimate tensile strength that could resist 58.062N of force. This could be due to the hair fibres' tendency to distribute evenly throughout the mixture and not tangle with each other to form clumps, which possibly reduced the tensile strength of the hemp and flax samples. The 25% hair sample was also stronger than the 25% hemp and flax samples.

The higher the tensile modulus, the more brittle a material is. Generally, the 25% reinforced samples are the least brittle. With the control samples, on a force vs. time graph, the point of breakage was a clearly defined high point characterized by a gradual increase in force followed by a drastic decrease. The graphs of the reinforced samples indicated that a certain part of the sample would fracture first, likely the matrix, forming the first peak on the graph, and then as force was continually applied the fibres would break or be pulled from the matrix, forming successive peaks.