While plant-based alternatives to petrochemical plastics are an attractive option, plant protein-based bioplastics present their own challenges. Specifically, many plant-protein bioplastic studies are targeted toward biodegradable food packaging materials. The food packaging industry poses some significant challenges with diverse mechanical and barrier property requirements. Natural materials often require modification in order to provide suitable performance. Incorporating Olive Stone Powder into such plant-based systems has demonstrated successful improvement on such properties.
Two commonly studied proteins for bioplastic formation are soy protein from soybean and Zein from corn maize. Each protein has some promising physico-chemical properties, yet still requires modification in order to be adequate for food packaging application. Unmodified soy protein films demonstrate good flexibility while lacking strength and water resistance. On the contrary, Zein-based bioplastics exhibit high strength and good water resistance yet have very little flexibility. Therefore, primary areas in need of advancement are:
| Soy Protein | Zein |
|---|---|
| 1. Strength | 1. Flexibility |
| 2. Hardness | 2. Hardness |
| 3. Barrier Properties | 3. Barrier Properties |
Often, synthetic material additives are utilized in order to achieve these advancements in bio-based films, however, those modifications do not address the environmental risk of conventional plastic materials. For that reason, Olive Stone Powder is a promising sustainable material which could be used to enhance performance of soy protein and Zein-based bioplastics.
Olive Stone Powders as Additives for Degradable Packaging Bioplastic Films
Indeed, by incorporating Olive Stone Powder into soy protein-based bioplastic films, significant improvement of all desired properties was achieved.
Figure 1. Tensile (left) and pendulum hardness (right) testing of bioplastic films based on soy protein in the presence of various amounts of olive stone powder.
The strength of these modified films increased by 300%. Furthermore, moisture resistance can be expected to be enhanced based on significant increase of water contact angle, and hardness of the product nearly doubled with as little as 0.35wt% Olive Stone Powder. Thus, addition of Olive Stone Powder in soy protein-based films successfully addresses all three areas of improvement required for future food packaging applications (Figure 1).
Likewise, upon addition of Olive Stone Powder into the Zein-based bioplastic films, advanced results were achieved (Figure 2).
Figure 2. Figure 1. Tensile (left) and pendulum hardness (right) testing of bioplastic films based on Zein in the presence of various amounts of olive stone powder.
Tensile strength of the material and flexibility increases more than 500% and no loss of moisture is noted. Again, significant enhancement of films hardness was seen with greater than 200% increase with only 0.1wt% of Olive Stone Powder. These results suggest promising use of Olive Stone Powder as a modifier for biobased food packaging materials.
Of additional importance is the appearance of such biobased plastics films. Since many synthetic food packages permit the consumer to see the product inside, alternatives to petro-chemical based materials should likewise allow the consumer to see the food product which is within the package. This is a significant challenge when utilizing plant proteins, as these, although transparent, typically result in a light eggshell-to-yellow color. Therefore, any additives used to modify the bioplastic, should not result in opacity of the film or further discoloration, so as to allow the packaged food to be clearly seen.
Upon incorporation of the Olive Stone Powder into the described soy and Zein protein film systems, appearance of the bioplastics remains transparent, smooth, and nearly colorless. (films prepared from Zein have a slightly more yellow color due to the protein not the Olive Stone Powder) (Figure 3).
Figure 3. Olive Stone Powder modified soy and Zein bioplastic films on the BioPowder logo to show transparency and film appearance.
These results are especially promising as they demonstrate that by utilizing Olive Stone Powder as natural additive in protein-based systems, it may be possible to prepare 100% biobased thermoplastic films. These modified, all-natural bioplastics demonstrate enhanced strength, flexibility, moisture resistance, and film hardness. Further use of Olive Stone Powder should be explored in order to continue moving away from synthetic materials and encourage sustainable products in the food packaging industry.
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