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Polyvinyl Alcohol-Based Biocomposites and Bionanocomposites: State-of-the-Art, New Challenges and Opportunities

Visakh P. M.*

Department of Physical Electronics, TUSUR University, Tomsk, Russia

Abstract

This chapter presents the recent advances in the field of polyvinyl alcohol-based biocomposites and bionanocomposites and their new challenges and opportunities. In this chapter, we will be discussing mainly short abstract for all chapters in this book, with different topics, such as biodegradation study of polyvinyl alcohol-based biocomposites and bionanocomposites, polyvinyl alcohol-based biocomposites and bionanocomposites: significance and applications, practical step toward commercialization, polyvinyl alcohol/cellulose-based biocomposites and bionanocomposites, polyvinyl alcohol/starch-based biocomposites and bionanocomposites, polyvinyl alcohol/polylactic acid-based biocomposites and bionanocomposites, biomedical applications of polyvinyl alcohol-based bionanocomposites and hybrid interpolymeric complexes.

Keywords: Polyvinyl alcohol, biocomposite, bionanocomposites, biodegradation, nanocomposites, hybrid interpolymeric complexes, biomaterials

1.1 Biodegradation Study of Polyvinyl Alcohol-Based Biocomposites and Bionanocomposites

PVA applications cover the research areas of formulation films, synthesis of coatings, adhesives products, and emulsion polymerization. Globally, PVA production and consumption was assessed nearly 1.124 million tons in 2016. Polyvinyl alcohol (PVA) exhibits the properties, such as thermo-stability, water solubility, film forming, high viscosity, emulsifying, tensile strength, and flexibility [1]. In biodeterioration, the microbial biofilm populates the surface of substrate on which they initiate apparent biodegradation. This changes the morphology of the surface into more rough and deformed. Later, deplolymerization involved extracellular enzymes, which are secreted by microbial cells. Enzymes catalyze the breakdown of bonds in polymers and produce low molecular weight products like oligomers, dimers, or monomers. Meanwhile, physical and chemical degradation has several disadvantages, such as incomplete decay efficiency, higher cost and by-product pollution [2]. In comparison, microbial and enzymatic degradation is drawing increased attentiveness because of high efficiency, low cost, and more economic and environmental protection compared with physical-chemical degradation [3]. Various microorganisms have been found useful for biodegradation of PVA. Diversity of PVA biodegraders has been cited in literature, which spans from natural source, like activated sludge, soil, and biodegradable support, like polymeric sheet. These strains of microorganisms have shown their ability to efficiently assimilate PVA as carbon source in growth medium. These microorganisms are studied either as a pure culture or mixed culture to demonstrate better activity on PVA [4].

A few strains of bacterial and fungus that have been utilized for PVA biodegradation reported are Pseudomonas, Alcaligenes, and Bacillus. Penicillium WSH02-21, Actinomycete, Streptomyces venezuelae GY1 strain. Aspergillus foetidus. The expression of the PVA enzymes can be inducible under appropriate conditions. Bacterial species that utilize PVA have been found from sludge samples by providing PVA as a selective source of carbon. PVAase, an enzyme that degrades PVA, secreted from Bacillus niacin immobilized by cross-linking as enzyme aggregates has shown improved enzyme activity approximately 90% compared with free PVAase. Non-purified PVAase can increase the usability for its large-scale application in the industry [5]. Recyclable biocomposites derived through naturally degradable polymers are prepared to make composition attractive. This strategy enhances biocomposites properties after blending with another nanosize biodegradable filler material for better processability, usability and extending life of end-use application [6]. The orange peel powder-improved properties of PVA films and make the PVA suitable for packaging application [7]. The biodegradability feature of PVA nanocomposite films lessened in a certain degree by modification with expensive inorganic nanoparticles of graphene oxide nanosheet [8], calcium carbonate nanoparticles [9], ZnO and nano-SiO2 [10]. These nanocomposite films have showed significant improvements in the barrier performance due to presence of nanofillers.

Biodegradability of PVA/cellulose composites functioned at 22°C to 27°C and relative humidity ranges 70% to 80%. Samples had displayed a fast weight loss in 16 days in a soil burial test. Weight loss has decelerated in the succeeding soil burial period after 16 days. Their work concludes that the cellulose biodegradability rates are higher than PVA in ecocomposites which resulted in higher weight loss with better biodegradability than that of neat PVA. In biodegraded biocomposites, recovery and analysis of constituent make the composites from complex matrix, like soil compromised the study outcome. For example, cellulose fiber collection from soil after the first 16 days of biodegradation of PVA/cellulose in a buried soil severely hinders degree of biodegradation under natural decomposing conditions. PVA mixed with cellulose prepared through 40 cycles of pan milling was more possible to biodegrade than cellulose obtained through single cycle of pan milling. Higher number of cycles of pan milling reduces the size of cellulose fibers <20 µm and less crystalline, which promote the substrate utilization activity for microorganisms through enhanced sub-strate-microorganism interaction in the soil [11].

The composition of PVA/nanowhiskers biocomposites discloses its biodegradable and environmental friendly biomaterials with utilization as a food source after disposal in a manner that has a positive effect during natural degradability. Strengthening of poly(vinyl alcohol) nanocomposites after the addition of alpha-chitin nanowhiskers has shown improved mechanical properties [12], which possibly increased the resistance to biodegradation. Machine-driven reinforcement of PVA tricomponent nanocomposites with chitin nanofibers and cellulose nanocrystals known for better thermal properties [13], which reduces the biodegradability under ambient temperate conditions. In fact, tricomponent nanocomposites change their mechanical and thermal characteristics that turn them into high-performance biomaterials with possible low environmental impact. The PVA/CS film amalgamated with various concentrations of CNC, which were 1, 3, and 5 wt%. The PVA/CS/CNC bionanocomposite film demonstrated excellent response as antifungal and antibacterial activity, a property which is mandatory and associated with potential films for food processing industry [14]. PVA has special interest in biocomposites as it has the ability to reduce antioxidant and antibacterial activities against gram-positive and gram-negative bacteria tested [15]. The mixing of PVA into chitosan has remarkably accepted as a new way to obtain films with promising biodegradability while retaining reasonable antioxidant and antibacterial properties. It provides balanced biocomposites with good strength, biodegradability, and application in extending the shelf life of packed food.

1.2 Polyvinyl Alcohol-Based Biocomposites and Bionanocomposites: Significance and Applications, Practical Step Toward Commercialization

Key raw material to prepare PVA is the vinyl acetate monomer. The monomer is manufactured through the polymerization of vinyl acetate. Instead, it goes through partial hydrolysis, which consists of partial substitution of the ester group with the hydroxyl group in vinyl acetate, completed in the presence of aqueous sodium hydroxide. The PVA is precipitated, washed, and dried after gradual application of the aqueous saponification agent. When making the polyvinyl alcohol solution, it is recommended to use tap water, as bacteria grow faster in PVA containing distilled water. This allowed macromolecules to form crystallites, stabilizing the films and inducing a chemically cross-linked behavior. It has outstanding optical properties, great dielectric power, and excellent capacity for storing charges [16]. Doping with nanofillers can readily customize its mechanical, optical, and electrical attributes. Hermann and Haehnel first synthesized it in 1924 by saponifying the poly(vinyl ester) with a solution of sodium hydroxide resulting in a PVA solution [17]. PVA's physicochemical and mechanical properties are governed by the number of hydroxyl groups contained in the polymer PVA [6]. Different grades of PVA are available on the market based on hydrolysis (percent) and molecular mass and have different characteristics, including melting point, viscosity, pH, refractive index, and band gap [18]. The consequence of variation of the length and the degree of hydrolysis of vinyl acetate under acidic or alkaline conditions results in different PVAs having different durability, tensile strength, density, emulsification extent, dispersing capacity, etc.

PVA has a high melting point, due to hydrogen bonding in the matrix. Interfaces play a crucial role in understanding material behavior, such as PVA. One downside to dealing with bulk materials is the presence of a small fraction of atoms at the interfacial surface. One major problem in the manufacture of polymeric nanocomposites is the uniform dispersion in polymer matrix of nanofillers....