Improvement of mechanical properties of polylactic acid with modified natural rubber

Nowadays, petroleum-based polymers are frequently used in engineering and advanced applications and in the production of polymeric products. The foreseen and underlined decrease in oil resources, with the imbalance in prices, difficulties in the production of synthetic polymers and the supply of raw materials in the competitive global market are some examples of the serious concern. Another problem is the apprehension of environmental pollution due to the petroleum-based polymers remain as non-degradable waste materials in nature. Polylactic acid (PLA), which is the most preferred biopolymer in the packaging industry in recent years, has limited usage areas due to its poor mechanical properties. Improving the mechanical properties of PLA has gained importance to maintain its biomaterial property in order to expand its usage in other fields. At this point, the preparation of PLA blends with natural rubber, which is an another biopolymer, will allow the development of a brand new biomaterial with better mechanical properties. In this thesis, natural rubber (NR) is modified to acquire homogeneous blends with PLA, for improving mechanical properties. NR is first epoxylated and then epoxy groups are acetylated to introduce ester groups to the structure, thus it is aimed to ensure compatibility with PLA in the ester structure. With FTIR and 1H-NMR analysis, it is found that NR is successfully epoxilated approximately 30%, and acetylation reaction was successfully introduced to the structure by about 10%. Then, PLA/NR, PLA/ENR, and PLA/ANR blend films containing 25, 50 and 75% PLA are prepared and their thermal, morphological and mechanical properties are examined. To determine thermal transitions of the blends, from DSC analyzes it is found that Tg values did not change in NR-containing blends, however, Tg values increased as the amount of PLA decreased in ENR and ANR blends. When the OM and SEM images of the blends are examined, it is observed that PLA/NR blends have a heterogeneous structure, while PLA/ENR blends have a homogeneous structure. Also, in PLA/ANR blends, a heterogeneous structure with a regular distribution of circular regions is formed and the matrix is formed by PLA in 25 and 50% ANR containing blends, whereas ANR is the matrix in 75% ANR content. According to the mechanical tests applied to the blends, the elongation and ultimate strength values of the ENR at break are higher than those blends with NR and ANR. However, ANR blends are found to have higher yield strength and breaking strength. In addition, fluctuations are observed in stress-strain curves due to the simultaneous separation of heterogeneous regions from each other during tensile tests of PLA/NR blends. %25 ANR containing blend has the highest yield strength, tensile strength, and elongation at break with the values of 7,5 N/mm2, 11 N/mm2 ve 205%, respectively.