Introduction

1. Introduction

The development of biodegradable polymers has been a subject of great interest in materials science for protection of environment. Biodegradable polymers can be degraded upon disposal in bioactive environments by organisms, such as bacteria, fungi and algae or by hydrolysis in buffer solutions or seawater. Several applications have been proposed for these polymers in the fields of medicine, agriculture and packaging.

Generally, biodegradability is exclusively a function of the polymer structure and does not depend on the origin of the raw materials – whether petrochemically based or from renewable resources. At present, synthetic biodegradable plastics provide a number of advantages compared to those made from naturally produced macromolecules (Starch, cellulose, etc.) such as better use properties, processability comparable to conventional plastic, constant material quality and significantly inherent biodegradability. Besides the natural polyesters (PHB), many other synthetic aliphatic polyesters are susceptible to microbial attack. Recently, it was shown that synthetic co-polyester containing aromatic constitutes are also degraded by microorganisms. The degradation decreases as the amount of aromatic components increases.

However, some drawbacks have prevented its introduction in the market as a valid alternative to the currently wide spreads non-degradable oil-based thermoplastics. Some of these drawbacks are its fragility, thermal degradability at temperature not far above the melting point, and its high price. Preparations of blends or composites are the most common routes to improve properties. A new area of composites called nanocomposite, in which the reinforcing material has nanometric scale. Nanotechnology has been described as the next great frontier of material science.

Polymer layered silicate nanocomposites have received considerable attention in the recent years. At minimal concentration of nanofiller to the tune of 1%, there has been a concurrent improvement of mechanical thermal, optical and physico chemical properties as compared with a conventional micro/macro composite. The layered silicates used in the preparation of phyllosilicates and more precisely 2:1 phyllosilicate. The clay morphology consists of layers of tetrahedral silicate sheets (Si, Al) and octahedral hydroxide [Mg (OH)₂ or Al(OH)₃] sheets. The tetrahedral sheet consists of individual silica tetrahedral, which shares three out of four oxygen atoms, forming a plane sheet. The octahedral sheets consists of an individual octahedron sharing edges composed of oxygen and hydroxyl with positively charged species Al, Mg, Fe ⁺⁺⁺ and Fe⁺⁺ which serve as coordinating cations. The layered silicates with a thickness of 1 nm have a very high aspect ratio, ranging between 10 to 1000 that creates an effective surface area for polymer filler interaction leading to property enhancements in the virgin matrix. Tailoring composites with a perspective of sustainable development and ecofriendly characteristics have resulted in renewed interest in natural renewable resource based and compostable materials. Research effects in the areas of natural fiber based plastics; biodegradable polymers, starch based plastics etc. have already been undertaken with a primary focus on development of biodegradable composites with environmentally safe characteristics and desired attributes.

Incorporation of nano scale fillers can significantly enhance the mechanical, thermal, dimensional and barrier performance in the biodegradable polymers. Biodegradable nanocomposites can be prepared using various methods such as solution intercalation, melt intercalation, in-situ intercalative polymerization and template synthesis. Polymer melt intercalation has been proved to be a versatile technique in the fabrication of biodegradable nanocomposites because of its environmental friendly characteristics and compatibility with the nanofillers. Several attempts have already been made in the fabrication of poly lactic acid (PLA), poly caprolactone (PCL) , poly butylene succinate (PBS), based nanocomposites using melt blending technique. PBAT, an aromatic aliphatic biodegradable co-polyester, is a flexible material with a higher elongation than PLA and PBS and suitable for various packaging and agricultural applications.

The present article summarizes an extensive investigation on physico-mechanical and thermal characterization of PBAT bio-nanocomposites. PBAT is a biodegradable, statistical, aliphatic-aromatic Copolyester based on the monomers butanediol, adipic acid and terephthalic acid. It has properties similar to LDPE because of its high molecular weight and its branched molecular structure. A detailed analysis on variation of mechanical, thermal, dynamic mechanical and morphological characteristics of bio-nanocomposite of PBAT with various organically modified nanoclays has been made. Further the rate of biodegradation with the incorporation of nanoclays has also been investigated.