Environmental Silicate Nano-Biocomposites

The last two decades have seen the development of an alternative chemistry, a green chemistry, which intends to reduce the human impact on the environment. The polymers are obviously involved into this tendency and numerous biodegradable plastics are now processed for a wide range of applications such as packaging, leisure, agriculture, and biomedical. Some of these polymers combine renewability and biodegradability, such as polylactide, polyhydroxyalkanoate, and the polysaccharides. However, even if a lot of commercial products are now available, their properties (mechanical properties, moisture sensitivity …) have to be enhanced to be really competitive with the conventional petroleum-based plastics. One of the most promising answers to overcome these weaknesses is the elaboration of nano-biocomposites, namely the dispersion of nano-sized filler into a biodegradable matrix. This introductory chapter intends to briefly highlight some recent studies and developments on nano-biocomposites systems mainly based on nanoclay.

In the recent years, bio-based and biodegradable products have raised great interest since sustainable development policies tend to expand with the decreasing reserve of fossil fuel and the growing concern for the environment. These polymers bring a significant contribution to the sustainable development in view of the wider range of disposal options with minor environmental impact. As a result, the market of these environmentally friendly materials is in rapid expansion, 10–20 % per year. Consequently, biodegradable polymers are the topics of much research. Biodegradable polymers can be mainly classified as agro-polymers (starch, chitin, protein…) and biodegradable polyesters [polyhydroxyalkanoates, poly(lactic acid)…]. These latter, also called biopolyesters, can be synthesized from fossil resources but main productions are obtained from renewable resources. This chapter intends to present these polymers regarding the synthesis, the structure, properties and their applications.

This introductory chapter presents the most relevant structural, physical, and chemical properties of clay minerals for the formation of nanocomposites with polymers. The general principles of silicates classification are outlined in order to better understand the structures of the various types of clay minerals as phyllosilicates. Cation exchange capacity (CEC), surface area, porosity, and rheological properties of clay minerals are briefly discussed. The physico-chemical properties of clay mineral layers, including the reactivity at the edges surfaces, are introduced together with their consequences for the various mechanisms of clay-polymer interactions. The chapter closes on a brief presentation of synthetic clay minerals and a general introduction to clay polymer nanocomposites.

Polymer/layered filler nano-composites (PLFNCs) offer remarkably improved mechanical and various other properties with low inorganic filler loading. The major development in this field has been carried out over last one and half decades. However we are far from the goal in terms of understanding the mechanisms of the enhancement effect in the nano-composites. Continued progress in nanoscale controlling, as well as an improved understanding of the physicochemical phenomena at the nanometer scale, have contributed to the rapid development of novel PLFNCs. This chapter presents recent advances in biodegradable polylactide (PLA)-based nano-composites with the primary focus of recent advances from basic science to technology.

Poly(ε-caprolactone) is a biopolyester synthesized from fossil resources with interesting biodegradable properties. However, for certain applications, this biopolymer cannot be fully competitive with conventional thermoplastics since some of its properties appear too weak. The association of PCL with nano-sized fillers allows for significantly improving a large range of properties. The most reported nano-fillers in poly(ε-caprolactone)-based materials are represented by organo-modified clays more likely leading to one of the most widely investigated families of nano-biocomposites. This chapter is dedicated to this novel class of materials with a special focus set on the relationships between the production process, the extent of nano-filler dispersion and the thermo-mechanical properties, e.g., crystallinity and stiffness, of the related nano-biocomposites.

Polyhydroxyalkanoates or PHAs were first observed in a laboratory in France in the 1920s and, since then, their creation as a form of energy storage in bacteria as well as their practical uses have been much studied. There has been increased interest in commercial production of PHAs in recent times and, over the past 10 years in particular, there have been various reports on solution-cast or melt-processed PHA/clay nano-biocomposites and their properties. In most studies, these nano-biocomposites exhibit intercalated or mixed exfoliated/intercalated morphologies. The use of plate-like clays as additives can lead to some enhancement in the mechanical and gas barrier properties of PHAs as well as increased thermal stability, although the effects depend significantly on clay type, clay organomodifer and process conditions. The influence of clay addition on PHA biodegradability has been either positive or negative according to the particular study. There has been very little research to date on the migration properties of PHA in the context of use in packaging and none yet in which PHA/clay nano-biocomposites have been the focus. If economic and technical challenges can be solved, PHAs should have a promising future in various uses ranging from packaging through to medicine and PHA/clay nano-biocomposites may also play a role in the future by providing a way for PHA material properties to be tuned according to the particular need.

In the recent years, biodegradable aliphatic polyesters-based composite materials have attracted substantial interest, primarily due to their sustainable production, use and end-life. This chapter discusses the preparation, characterisation, and properties of nanoclay-containing composites of biodegradable poly(butylene succinate) (PBS) and poly[(butylene succinate)-co-adipate] (PBSA). Various nanocomposite structures arising from the incorporation of layered silicate particles, both pristine and organically modified, into the neat PBS and PBSA matrices is critically reviewed. Good dispersion of the layered silicates, especially the organically modified layered silicates, tends to result in an improvement in a number of properties of the final nanocomposites: storage modulus, tensile modulus, gas barrier properties, degradability, and thermal stability, when compared with the neat polymers.

Despite the numerous studies reported on clay-based nano-biocomposites, only few articles concern works on PBAT/clay nano-biocomposites. However, in these studies, a large number of organo-clays has been tested to elaborate PBAT nano-biocomposites. Most of the reported works use the melt-intercalation route to elaborate such nanohybrids materials. According to the morphological analyses, nano-biocomposites with intercalated structures are mainly obtained and clay exfoliation seems difficult to reach in these systems. The best results in terms of clay dispersion and material properties are obtained with organo-clay bearing hydroxyl group and thus having better polarity matching with the matrix. For all intercalated structures, the clay addition has a limited beneficial effect on mechanical and thermal properties whereas the clay platelets dispersion seems to influence the PBAT crystallization with enhanced nucleation. Even if a large majority of the re-ported studies deals with montmorillonite clay, interesting results were also obtained with hectorite.

In this chapter we focus on the barrier properties of nanocomposite of biodegradable polyesters with layered inorganic fillers. First of all, to better understand the influence of the lamellar inorganic fillers on the permeability, the theory of permeation and the barrier models so far developed for polymer nanocomposites are reviewed. Afterwards the barrier properties of the most important biodegradable polyesters filled with inorganic lamellar solids, such as Polylactic acid (PLA), Polycaprolactone (PCL), Polyhydroxbutyrate (PHB), and Polybutylenesuccinate (PBS) are reviewed and the outstanding results enlightened. As a general trend, the best improvement of barrier properties is related to the exfoliation of clay platelets into the polymeric matrix, and this in turn is dependent on the chemical structure of the clay, the organic modification, the filler concentration and the processing procedure to prepare the composite. Where possible, all these parameters were reported and correlated with the final properties. Also the contrasting effect of clays on the two parameters determining the water permeability, that is sorption and diffusion, is reported in many cases.

In these years we are witnessing the growth of the biopolymers durable application markets such as buildings, transportation, electronic equipments etc. Thus, the fire retardancy issue is becoming important and it is expected that in the next future more and more research will be devoted to the subject. So far, a limited number of papers reports on flame retardant properties of biopolyesters and they are mainly on polylactide. Most of the papers published on this topic regarding biopolyesters, concern polyesters fire retarded by traditional fire retardants developed for oil sourced polymers, especially polyesters such as polyethylene terephthalate or other polymers such as polycarbonate. The recently developed use of nanoclays to fire retard polymers has proved to be beneficial also for polyesters from renewable resources. This chapter reviews the studies published on thermal and fire behaviour of polylactide nanocomposites based on clays. Indeed, PLA is the most important commercial plastic from renewable resources (RRP) polyester for which durable applications are being developed and fire retardant aspects are investigated.

The aim of this chapter is to describe the main studies and results on starch-based nanocomposites reinforced with clay particles. This particular combination leads to the formation of a nanocomposite material with novel properties. However, a good knowledge about starch (structure, type, chemical and physical modification) and its rheological behaviour is necessary for developing these nanocomposites. Many factors and processing parameters affect the final properties of the starch based nano-biocomposites. The main factors which influence the mechanical properties of the nano-biocomposites will be analyzed such as the type of clay, the chemical modification of clay, the type of plasticizer, the water humidity test conditions, the use of chemically modified starches, the thermal stability and water absorption. In addition, the influence of different processing techniques and mixing methods will be studied.

In the current context, protein-based materials might be considered as an alternative to the petroleum-based plastics since fully biodegradable and characterized by remarkable functional properties that can be exploited in a wide range of non-food applications. To improve their performances that are often restricted by high water sensitivity and low mechanical properties, a relevant strategy consisted in the development of protein/clay nanocomposite. For this purpose, several examples of protein-based nano-biocomposites were presented with a special attention for the methods used for the incorporation of layered silicates (organically modified or not) into the matrices and the ultimate functional properties exhibited by the resulting materials. In terms of mechanical properties, the addition of nanoclays leads to a significant improvement of material performance with an increase of Young’s modulus and tensile strength ranging between 1.5 and 2 times. As regards as barrier properties, the improvement appeared quite moderate in spite of a rather good dispersion of layered silicates that would be expected to result in a tortuous pathway limiting diffusion of gases molecules. Thus, a two-fold reduction in water vapour permeability was obtained, and the same or no effect in the case of permeability toward O₂ and CO₂.

Plant protein-based clay nano-biocomposites were analyzed through a series of material characterization technologies including x-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. Efficient dispersion of nanoclay in soy proteins or wheat gluten matrix was achieved via ultra-sonication treatment of the clay nanoparticles in plasticizers or using chemically modified clay nano particles. The dispersion status of the nanoclay in the composites were examined by XRD and TEM respectively and correlated to the changes in molecular motions and glass transitions of the protein matrixes to explore the effect derived from the nanoclay particles. High-resolution solid-state NMR further provides the interaction between the nanoclay and each component in the wheat gluten matrix, and the whole phase structures of the protein matrix. To correlate these results to the physical properties of the nanocomposites is fundamental to understand the performance of the systems and design new protein clay nanocomposites.

The present review chapter includes an overview on the current state-of-art of chitosan-clay based bio-nanocomposites. In the same way than conventional nanocomposites, these biohybrid materials also exhibit both structural and functional properties together with biocompatibility and biodegradability, which can be of great interest for different applications. Four main areas of interest have been identified showing examples of applications as green nanocomposites, bio-nanocomposites addressed to biomedical purposes (tissue engineering and drug delivery), environmental remediation and electroanalytical devices. Finally, examples of bio-nanocomposites based on chitosan assembled to other inorganic solids have been introduced to show the versatility of this biopolymer for development of diverse type of advanced functional materials.

The main directions in food packaging research are targeted towards improvements in food quality and safety. For this purpose, food packaging providing longer product shelf-life, as well as the monitoring of safety and quality based upon international standards, is desirable. New active packaging strategies represent a key area of development in new multifunctional materials. Nanotechnology can help to address these requirements and also with other packaging functions, such as food protection and preservation, marketing and smart communication to consumers. The use of nano-biocomposites for food packaging combines two of the most active research areas on materials in contact with food. Thus, applications of nano-biocomposites could help to provide new food packaging materials with improved mechanical, barrier, antioxidant and antimicrobial properties. From the food industry standpoint, concerns such as the safety and risk associated with nanomaterials, migration properties, possible ingestion considering mechanisms for nanoparticles to interact with the human body and regulations on the use of nanotechnology need to be considered The latest innovations in food packaging and the use of nano-biocomposites are reviewed in this chapter. Legislative issues related to the use of nanomaterials in food packaging systems are also discussed.

This chapter summarizes the state of the art in biodegradation and applications of nanobiocomposites. Specifically we examine the biodegradation of various biopolymer nanocomposite classes (starch, PLA, PCL and PHA matrix polymers) in various environments (soil, compost, marine) and then discuss the development of new biodegradation standards. We then examine applications and research focused to new applications for the same range of materials, before focusing on some key application areas. It is clear that development of nanobiocomposites in a systematic, tailored fashion increases the application areas whilst maintaining biodegradability in various environments for a range of biopolymer matrices.