Starches, both native and modified, have been used for a long time to make various products. Nontraditional starches, which have good thickening and gelling properties, are used in food products and are important food sources for some poor nations. Recently, researchers have been working on developing biopolymers from alternative sources, including nonfood sources, to improve the physicochemical and functional characteristics of starch.
Romero-Bastida et al. (2005) conducted a study comparing films made from nonconventional starch sources, such as banana, mango, and okenia, using both cold with NaOH and thermal gelatinization. They analyzed the films’ structural, mechanical, and water vapor barrier properties using SEM observations. The results showed that films obtained through hot gelatinization had a homogeneous matrix, while those obtained through cold gelatinization had a cracked structure. This finding was linked to the poorer water barrier and mechanical resistance of films obtained through cold gelatinization.
Galdeano et al. (2013) studied oat starch films and sheets with glycerol, sorbitol, and urea as plasticizers at different humidities. Oat starch contains more lipids than other starches, making it a good choice for film formulations. However, the films were still unstable at high humidity, causing a decrease in strength and an increase in deformation. Sorbitol was the most effective plasticizer and urea surprisingly had similar mechanical properties to other plasticizers. Extrusion resulted in more open and fragmented structures.
Thermoplastic starch reinforced with residual lignocellulosic fibers, such as husk, is a promising composite material due to the natural affinity between the fibers and the seeds where starch is formed.
Starch isolated from ripe pehuen seeds collected in the Chilean forest was used to prepare starch-based composites, reinforced with pehuen husk, by injection molding at 50°C and 300bar. The composites showed good thermo-mechanical properties and a strong interaction between the fibers and the plasticized starch matrix due to the natural affinity between husk and starch in the pehuen seed.
The sugar palm tree is a forest species found in Malaysia, and its starch can be used to make a biodegradable polymer that can be reinforced with natural fibers to create green composites. This composite is renewable, biodegradable, inexpensive, and readily available in tropical countries like Malaysia, Indonesia, Cambodia, and the Philippines.
Sugar palm starch (SPS) has superior amylose content compared to other starches like tapioca, sorghum, potato, wheat, and maize. Researchers studied the properties of SPS and successfully developed thermoplastic starch from sugar palm tree by adding different quantities of glycerol as a plasticizer.
SPS-based films could be used as an alternative to petroleum-derived plastics for food packaging to manage environmental waste. A recent study evaluated the effect of different plasticizer types and concentrations on the mechanical and thermal properties of SPS films. While the tensile strength of the films decreased with increasing plasticizer concentration, their elongation percent increased. Plasticized films with sorbitol showed high thermal stability, and the authors recommended further research to enhance the functional properties of sugar palm-based films for effective food packaging material.