Particulate starch, its effects as a filler in high density polyethylene
Rapid advances continue in the acquisition 6f new fundamental knowledge of starch and a vigorous expansion in the use of starch is proceeding in both food and non-food applications. Results are here reported on starch-filled high density polyethylene which reveal reinforcement effects of starch on the thermoplastic. This significant development makes starch a most promising organic filler. This work is primarily a study of the mechanical and thermal properties of starch-filled high density polyethylene and attempts to identify changes caused in the structure of this polymer due to starch filler. Particular attention has also been given to changes in crystallinity and microscopic appearance. Because preliminary studies showed that enhanced effects were obtained when using starches of small particle size, much effort was given to developing a simple method of extraction of starches from the many varieties of Taro (Colocasia esculenta) plants in order to get the best possible yield and freedom from agglomerates. Because of the absence of recorded data it was necessary to study the physical properties of these starches. The theory and application of small-angle light scattering was reviewed because of its value as a technique for the characterization of starches and spherulitic polymer studies. One hundred and twelve Taro starches were characterized in terms of average particle sizes by the above technique. Starches with particle sizes ranging from 3 micron to 50 micron were investigated in order to establish the size/effect relationship in starch polymer composites. Methods of increasing the adhesion between filler and polymer matrix have also been studied, as has also the stripping of amylopectin from starch grains by cold acid treatment. Acid treatment, surprisingly, produced composites of increased mechanical strength in high density polyethylene, implying that a true reinforcing filler has been created. Results from differential scanning calorimetry and x-ray diffraction studies revealed that an increase in degree of crystallinity in high density polyethylene was associated with the presence of starch.