Sugar palm tree is one of multipurpose trees grown in Malaysia. The inner part of sugar palm stem contains starch. It was used as raw material for starch and glue sub­stances.79 For the production of one ton of starch, ten to 20 trees are needed which suggests that one tree can produce 50 to 100 kg of starch.76 This accumulated starch is harvested from the trunk of matured palms (after 25 years) and can be applied as ‘green’ material. Starch will act as biopolymer in the presence of a plasticizer such as water, glycerol and sorbitol at high temperature. Previously, the characteriza­tion of sugar palm starch as a biopolymer have been done by using the glycerol as a plasticizers.76 From the research, it was found that the tensile strength of SPS/ G30 showed the highest value 2.42 MPa compared to the other concentration of the plasticizer. The higher the concentration of the plasticizers, the higher the tensile strength of plasticized SPS and optimum concentration was 30 wt.%. The tensile strength decrease to 0.5 MPa when concentrations of plasticizer was 40 wt.%. As the plasticizer content increased to 40%, not enough SPS to be well bonded with glycerol and thus poor adhesion occurred which reduce the mechanical properties of SPS/G40. This result well agreed with the finding of Laohakunjit and Noomhorm80 who claimed that the films outside this range are either too brittle (< 20 wt.%) or too tacky (> 45 wt.%).

Generally, as the plasticizer increase, the tensile strength and elongation of plas­ticized SPS increase, while the tensile modulus decreased. This phenomena indi­cates that the plasticized SPS is more flexible when subjected to tension or me­chanical stress. The results from this study prove the finding done by Beerler and Finney81 whereby they reported that the plasticizers such as glycerol will interfere the arrangement of the polymer chains and the hydrogen bonding. It is also most likely affect the crystallinity of starch by decreasing the polymer interaction and cohesiveness. Thus, this make the plasticized SPS become more flexible with the increasing of glycerol.

For the thermal properties, the Tg of dry SPS reaches 242.14 °C and decreased with addition of glycerol. This value was higher than Indica rice starch where Tg values was237°C.82 Meanwhile, Myllarinen et al.83 claimed that for dry starch the Tg reaches 227 °C. The sample with high glycerol concentrations showed lower Tg values and Tg of starch without plasticizer were higher than those of samples with glycerol (Table 9.3). This behavior was also observed by Mali et al.84 for yam starch and by Forssell et al.33, for films based on barley starch, in both cases with glycerol as plasticizer. According to Guilbert and Gontard85, plasticization decreases the in­termolecular forces between polymer chains, consequently change the overall cohe­sion, leading to the reduction of Tg. Mitrus86 has been claimed that the plasticizer decreased Tg because it facilitates chain mobility. Brittleness is one of the major problems connected with starchy material due to its high Tg.87 In the absence of plasticizers, starch are brittle. The addition of plasticizers overcomes starch brittle­ness and improves its flexibility and extensibility of the polymers.