In recent years, much attention has been focused on biodegradable polymers from renewable resources. Due to its availability and low cost, starch is a promising candidate among biopolymers for use in biodegradable packaging materials and for other purposes.
Starch-Based Polymeric Materials and Nanocomposites: Chemistry, Processing, and Applicationspresents the latest developments in starch chemistry, rheology, starch derivatives, starch-based nanocomposites, and their applications. The book also explores recent progress in biodegradable starch-based hybrids and nanomaterials and the incorporation of nanoparticles in starches to enhance their mechanical and thermal properties.
Starch-Based Polymeric Materials and Nanocomposites: Chemistry, Processing - Google книги
The book concludes by discussing the use of biopolymeric nanoparticles BNPs in drug delivery and life cycle assessment LCA of starch-based polymeric materials for packaging and allied applications. With contributions from leading experts in academia and industry, this volume demonstrates the versatility of starch and its potential in a variety of applications.
Jasim Ahmed'sresearch interests include food product development, food rheology and structure, novel food processing, and the thermal behavior of foods. His current focus is on bionanocomposites and application to food packaging. Blending starches aims to reduce the production cost; to improve barrier properties and dimensional stability; to decrease the hydrophilic character of starch; and increase its biodegradability Schwach y col. In order to optimize theoverall properties of such blends, starche sare blended with low molecular mass plasticizers such as glycerol, glucose, sorbitol, urea and ethylene glycol Priya y col.
The addition of plasticizers conduct to thermoplastic starch TPS , Tang y col. Depending on the type of the plasticizer blended with the starch, the final properties of the TPSdiffer. In general, plasticizers produce anincrease in flexibility, extensibility, and fluidity by reducing the strong intermolecular chain interactions. Additionally,TPS remains a very hydrophilic material Schwach y col. Recent advances in starch blending include blending TPS with biodegradable polymers is one of the most recent advancements mainly in food packaging applications Lu y col.
PVA is a synthetic biodegradable polymer that has the advantages of good film forming, strong conglutination, high thermal stability, and gas barriers properties Priya y col. The presence of PVA in a blend increases the mechanical strength, water resistance, and weather resistance of the blend Wang y col. Gelatinization is the most common method of blending starch with PVA; other methods might not be useful because of the gap between the thermo-degradation temperature and the melting temperature Wang y col.
The compatibility of the PVA and starch enables them to form a continuous phase at blending Lu y col. To improve the compatibility between PVA and starch, the addition of suitable plasticizers, cross-linking agents, fillers, and compatibilizers has been studied Priya y col. Some common plasticizers used in this blend are glycerol and water Tang y col. Both PVA and starch can be plasticized into a thermoplastic material, regularly using the casting method and glycerol in an aqueous medium Zhou y col. Both starch and PVA are biodegradable in several microbial environments; however, the biodegradability of PVA depends on its degree of hydrolysis and its molecular weight Lu y col.
Due to its biodegradable and hydrophobic characteristics, PLA has received considerable attention in the research of biomedical and packaging applications. To improve PLA's flexibility and impact resistance, numerous plasticizers have been incorporated such as poly ethylene glycol , glycerol, glucose monoesters, citrate esters, and oligomers. The hydrophilic properties of starch and the hydrophobic ones of PLA, cause low miscibility between the two compounds; for this reason, good melt-blending techniques and the addition of compatibilizers are required to increase successful interaction, i.
The degradation rate of PCL homopolymersis relatedtotheir molecular weight and degree of crystallinity. Thus, copolymerization of PCL with other aliphatic polyesters can improve its biodegradable ability. Singh y col. On the other hand, the presence of starch increases the rate of biodegradation of PCL because it intensifies hydrolysis reactions Vikman y col. In order to increase the compatibility between the two materials, the addition of an interfacial agent or compatibilizer is necessary.
Sugihy col. Blends of starch and PCL have been extensively studied during the last decade, although both high production cost and properties variation have limited its applications Singh y col. Reis et al. With adequate formulation and processing techniques,can be reduced the shortcoming of adhesion between starch and PHB-HV Wang y col. PBS is commercially available as a thermoplastic polymer.
Starch-Based Polymeric Materials and Nanocomposites : Chemistry, Processing, and Applications
Its high degree of crystallinityproduces low degradation rates which provide interesting properties such as excellent impact strength, high thermal stability, and good chemical resistance Suchao-in y col. The addition of starch to PBS improves its flexibility and increases its biodegradation time.
This way expanding its applications in packaging and flushable hygiene products is possible Wang y col. PBSA is an aliphatic thermoplastic copolymer synthesized by polycondensation of 1,4-butanediol with succinic and aliphatic acids. It has melt processability, good mechanical properties, biodegradability, and boththermal and chemical resistance Jbilou y col.
Maubane y col. Liao y col. The developingof starch blending tend to be more interesting while potential applications are extensive, and they can be able to substitute an older material that exhibits the same properties. Some important applications of starch- based biopolymers are summarized in Table 1. Table 1. Applications of starch-synthetic polymer blends.
Nanofillerscan be presented in different ways: spherical or polyhedral nanoparticles, nanotubes, and nanolayers. In all cases, these nanomaterials exhibit a large superficial area that improves adhesion between the composites of the polymer blend Ahmed y col. Xiey col. Phyllosilicatesare the nanofillers employed most often due to their availability, low price, and high aspect ratio. However ,polysaccharidenanofillers require acid hydrolysis during preparation, making their use not ecologically friendly Xie y col.
The principal effects of the addition of nanofillers in starch-based materials are:thermo-mechanical stability improvement,biodegradation increase ment and hydrophilicity reduction Xie y col. Starch-based nanocrystals are formulated from native starch granules under hydrolysis reactions of the amorphous regions, thereby releasing the crystalline lamellae Wittaya, This type of nanofiller involves low cost production, renewability, and environmentally-friendly characteristics Wittaya, The use of starch-based nanocrystals to reinforceelastomer-based matrixes shows a positive reinforcing effect evidenced by the increase of both stresses at thebreak and relaxed storage modulus Dufresne y col.
The main aspects that highlight by the addition of starch-based nano-biocomposites are the increase of values of strength at break and glass transition temperature, but also their disadvantages associated are related with the increment of water absorption and decomposition temperature Xie y col.
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During recent decades, the production and use of plastics has grown exponentially. Those plastic materials take an average of years to break down in the environment Villa y col. Some waste-management options available for plastics at the end of their useful life include recycling, incineration, and disposing of them in a landfill. In all cases, plastics cause a significant negative impact on the environment through the generation of pollutant gases and toxic substances such as dioxins, furans Wagner, , and endocrine disruptors Katami y col.
Some studies have been conducted to investigate new materials that employ biodegradable polymers instead of conventional ones Soroudi y col. In , the world production of bioplastics is expected to exceed six million tons European Bioplastics, Two basic methods are used in biodegradation assays: aerobic and anaerobic digestion.
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The activity of certain microorganisms decomposes biodegradable polymers into environmentally friendly components, e. Another type of biodegradation assay is to test the ecotoxicity using plant and animal species such as cress and earthworms Kyrikou, Some other non-standard tests based on the use of material exposure to specific microorganisms also exist Jayasekara, Tensile properties evaluated after a biodegradability assay are tensile strain, tensile strength, elongation, and tensile modulus.
A number of analytic techniques are also used: Fourier transform infrared increasing percentages of AMS. Other studies have been carried out in aqueous anaerobic environments with digested activated sludge from municipal wastewater treatment plants. The behavior of some blends in soil environments has been also analyzed. PVA and starch are biodegradable in some microbial environments; they are compatible and their blends present good film properties. A number of studies have been conducted to determine the biodegradability of these blends, here some of them are highlighted.
Starch and glycerol were totally degraded while PVA appeared practically intact. The blend characteristics were enhanced by surface modification with chitosan, which did not interfere with the biodegradation of the starch Jayasekara y col. Weight loss increased with increasing starch content and burial time. Thus, researchers concluded that as the starch content increases, the biodegradation rate also increases in most cases Tanase y col.
As the percentage of corn starch increased, the strength of the blends decreased.
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Specifically, bacteria and fungi isolated from the activated sludge of a municipal sewage plant and from a landfill biodegraded blends containing starch, PVA, and glycerol; the microorganisms consumed the starch, the amorphous region of PVA and the plasticizer Jayasekara, The results showed an increase in the rate of biodegradation as the starch content increased. On the other hand, a study based on the China National Standards also showed that the degradability increased with the addition of starch.
A number of studies exploring the biodegradability of starch-PLA blends in a variety of environments have been conducted. Researchers found that the addition of starch enhanced biodegradation of the PLA component, especially in liquid media Gattin y col. Regardless of the procedure applied in stage 2, the percentage of biodegradation was higher in the liquid medium than in the inert medium, The effects of starch and wood flour on the degradation of PLA-based blends were investigated by composting under ISO standard.
After 30 days, all of the samples tested were completely biodegraded, and no residuals were observed in visual inspection. The biodegradability and rate of biodegradation of the blends were investigated in a controlled environment using cellulose as control material. A study of the degradation of PLA and it blends with TPS submitted to degradation by tert-butyl hydroperoxide, myoglobin, and peroxide-activated myoglobin in simulated soil showed that TPS favored degradation of the material in all cases Rodrigues y col.
Studies using PLA, starch, and several compatibilizers or other substances have been conducted. The study of injection molded tensile bars indicated that weight loss increased with increasing starch and poly hydroxyester- ether PHEE contents. The blends were composed of various combinations of native cornstarch, PLA, and PHEE, and the bars were buried in soil for one year to determine the effects of the starch and PHEE on the rate of biodegradation Shogren y col.
The starch in the composite degraded almost completely in a soil environment within three months. The mechanical properties of the blends presented a reduction with regard to tensile strength at breakpoint especially in those with a higher starch content. PLA-g-AA was shown to be resistant to degradation as only a small decrease in weight was seen and only in weeks 7 to 12 Wu, The biodegradability increased with increasing starch content, and MA compatibilized blends showed higher biodegradability compared to those of blends without MA Jang y col.
All composites gradually degraded over time except pure PLA. The degradation rate increased as corn starch content increased Ohkita, Results indicate that adding PEG causes the blends to degrade faster with considerable weight loss and loss of mechanical properties. The degradation of the blends improved as TPS content increased. The samples containing PEG showed greater weight loss than the samples. The biodegradation of two PCL blends, one with dried granulated sago starch and the second with undried thermoplastic sago starch TPSS , was evaluated by the determination of weight loss and the amount of adipic acid liberated from PCL in one study.
Dried granulated sago starch presented an advantage in both the mechanical properties and biodegradation of the blend.