Recent Advances in Starch-Based Blends and Composites for Bioplastics Applications

Environmental pollution by synthetic polymers is a global problem and investigating substitutes for synthetic polymers is a major research area. Starch can be used in formulating bioplastic materials, mainly as blends or composites with other polymers. The major drawbacks of using starch in such applications are water sensitivity and poor mechanical properties. Attempts have been made to improve the mechanical properties of starch-based blends and composites, by e.g., starch modification or plasticization, matrix reinforcement, and polymer blending. Polymer blending can bring synergetic benefits to blends and composites, but necessary precautions must be taken to ensure the compatibility of hydrophobic polymers and hydrophilic starch. Genetic engineering offers new possibilities to modify starch inplanta in a manner favorable for bioplastics applications, while the incorporation of antibacterial and/or antioxidant agents into starch-based food packaging materials brings additional advantages. In conclusion, starch is a promising material for bioplastic production, with great potential for further improvements. This review summarizes the recent advances in starch-based blends and composites and highlights the potential strategies for overcoming the major drawbacks of using starch in bioplastics applications.

Preparation and Characterization of Biodegradable Composited Films Based on Potato Starch/Glycerol/Gelatin

The use of plastics is resisted worldwide. Therefore, finding alternatives to plastic packaging products is an urgent issue. This work was dedicated to the preparation of biodegradable composited films with potato starch, glycerol, and gelatin. The formulation of the biodegradable film was first optimized via response surface methodology combined with the multi-index comprehensive evaluation method that considered physical properties (thickness, water solution (WS), tensile strength (TS) and elongation at break (E%)) and barrier property (light transmittance (T%)). Results indicated that the optimal conditions were 2.5% starch, 2.0% glycerol, and 1.5% gelatin (based on water). The optimized film presented excellent properties with TS of 4.47 MPa, E% of 109.91%, WS of 43.64%, and T% of 41.21% at 500 nm, and the comprehensive evaluation score of the composite film was 28.68. Moreover, a model verification experiment was further conducted, which proved that the predicted value highly matched experimental values, indicting the credibility and accuracy of the model. The resulting films were further characterized on the basis of rheological measurements, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The rheological measurements proved that the film-forming solution exhibited low shear viscosity and non-Newtonian fluid behavior. FTIR and SEM revealed excellent compatibility among starch, glycerol, and gelatin. Hence, the resulting optimized film may be expected to provide theoretical basis and technical support for the food packing industry.

Microbial and Enzymatic Degradation of Synthetic Plastics

Synthetic plastics are pivotal in our current lifestyle and therefore, its accumulation is a major concern for environment and human health. Petroleum-derived (petro-)polymers such as polyethylene (PE), polyethylene terephthalate (PET), polyurethane (PU), polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC) are extremely recalcitrant to natural biodegradation pathways. Some microorganisms with the ability to degrade petro-polymers under in vitro conditions have been isolated and characterized. In some cases, the enzymes expressed by these microbes have been cloned and sequenced. The rate of polymer biodegradation depends on several factors including chemical structures, molecular weights, and degrees of crystallinity. Polymers are large molecules having both regular crystals (crystalline region) and irregular groups (amorphous region), where the latter provides polymers with flexibility. Highly crystalline polymers like polyethylene (95%), are rigid with a low capacity to resist impacts. PET-based plastics possess a high degree of crystallinity (30-50%), which is one of the principal reasons for their low rate of microbial degradation, which is projected to take more than 50 years for complete degraded in the natural environment, and hundreds of years if discarded into the oceans, due to their lower temperature and oxygen availability. The enzymatic degradation occurs in two stages: adsorption of enzymes on the polymer surface, followed by hydro-peroxidation/hydrolysis of the bonds. The sources of plastic-degrading enzymes can be found in microorganisms from various environments as well as digestive intestine of some invertebrates. Microbial and enzymatic degradation of waste petro-plastics is a promising strategy for depolymerization of waste petro-plastics into polymer monomers for recycling, or to covert waste plastics into higher value bioproducts, such as biodegradable polymers via mineralization. The objective of this review is to outline the advances made in the microbial degradation of synthetic plastics and, overview the enzymes involved in biodegradation.

Degradation Studies Realized on Natural Rubber and Plasticized Potato Starch Based Eco-Composites Obtained by Peroxide Cross-Linking

The obtaining and characterization of some environmental-friendly composites that are based on natural rubber and plasticized starch, as filler, are presented. These were obtained by peroxide cross-linking in the presence of a polyfunctional monomer used here as cross-linking co-agent, trimethylolpropane trimethacrylate. The influence of plasticized starch amount on the composites physical and mechanical characteristics, gel fraction and cross-link density, water uptake, structure and morphology before and after accelerated (thermal) degradation, and natural (for one year in temperate climate) ageing, was studied. Differences of two orders of magnitude between the degradation/aging methods were registered in the case of some mechanical characteristics, by increasing the plasticized starch amount. The cross-link density, water uptake and mass loss were also significant affected by the plasticized starch amount increasing and exposing for one year to natural ageing in temperate climate. Based on the results of Fourier Transform Infrared Spectroscopy (FTIR) and cross-link density measurements, reaction mechanisms attributed to degradation induced by accelerated and natural ageing were done. SEM micrographs have confirmed in addition that by incorporating a quantity of hydrophilic starch amount over 20 phr and by exposing the composites to natural ageing, and then degradability can be enhanced by comparing with thermal degradation.

Environmentally degradable sago starch filled low-density polyethylene

Degradable native low density polyethylene (LDPE) and modified LDPE films containing 5–30 wt% of sago starch, and LDPE with prodegradant additives in the form of a master batch (MB) in the amounts of 30% starch were prepared by twin screw extrusion followed by injection molding. Studies on their mechanical properties such as tensile strength and elongation at break and biodegradation were carried out by tensile test and exposure to hydrolysis, fungi environment as well as by natural weathering and burial in soil. The presence of high starch contents had an adverse effect on the tensile properties of the blend films. High starch content was also found to increase the rate of biodegradability of the films. The characteristic parameters of the environment were measured during the period of degradation and their influence on degradation of LDPE was discussed. Changes in weight, morphology, thermogravimetric analysis (TGA) and tensile properties of polymer samples were tested during the experiment performed.