Eduardo L. Canedo

Application of Infrared Spectroscopy to Analysis of Chitosan/Clay Nanocomposites

In recent years, polymer/clay nanocomposites have attracted considerable interest because they combine the structure and physical and chemical properties of inorganic and organic materials. Most work with polymer/clay nanocomposites has concentrated on synthetic polymers, including thermosets such as epoxy polymers, and thermoplastics, such as polyethylene, polypropylene, nylon and poly(ethylene terephthalate) (Pandey & Mishra, 2011). Comparatively little attention has been paid to natural polymer/clay nanocomposites. However, the opportunity to combine at nanometric level clays and natural polymers (biopolymers), such as chitosan, appears as an attractive way to modify some of the properties of this polysaccharide including its mechanical and thermal behavior, solubility and swelling properties, antimicrobial activity, bioadhesion, etc. (Han et al., 2010). Chitosan/clay nanocomposites are economically interesting because they are easy to prepare and involve inexpensive chemical reagents. Chitosan, obtained from chitin, is a relatively inexpensive material because chitin is the second most abundant polymer in nature, next to cellulose (Chang & Juang, 2004). In the same way, clays are abundant and low-cost natural materials. Although chitosan/clay nanocomposites are very attractive, they were not extensively investigated, with relatively small number of scientific publications. In addition, the successful preparation of the nanocomposites still encounters problems, mainly related to the proper dispersion of nano-fillers within the polymer matrix. In this chapter, in addition to discussing the synthesis and characterisation by infrared spectroscopy of chitosan/clay nanocomposites, data of x-ray diffraction and mechanical properties are also considered.

Melting and crystallization of poly(3-hydroxybutyrate): effect of heating/cooling rates on phase transformation

We studied the crystallization and melting phenomena of poly (3- hydroxybutyrate) (PHB), a biodegradable and biocompatible semi-crystalline thermoplastic, obtained from renewable resources. Its high crystallinity motivated several studies on crystallization and melting behavior, and also on ways to increase the amorphous polymer fraction. The effect of heating and cooling rates on the crystallization and melting of commercial PHB was investigated by differential scanning calorimetry. Several rates, ranging from 2.5 to 20 °C min –1 , were used to study the phase changes during heating/cooling/reheating cycles. The results showed that PHB partially crystallizes from the melt during the cooling cycle and partially cold crystallizes on reheating, and that the relative amount of polymer crystallizing in each stage strongly depends on the cooling rate. The melt and cold crystallization temperatures, as well as the rates of phase change, depend strongly on the cooling and heating rates.

Tailoring PBAT/PLA/Babassu films for suitability of agriculture mulch application

ABSTRACT Babassu was studied as a vegetable filler in a blend consisting of polybutyrate adipate terephthalate and polylactic acid aiming at preparation of bio-based and biodegradable films by solvent casting. The morphology, thermal, and mechanical properties were investigated with optical, thermoanalytical, and spectroscopic methods and correlated with the sample setup. Although only laboratory scale for film production has been applied in this work, the results suggest that the composite PBAT/PLA with 10% Babassu may be a suitable material for the application as agricultural mulch films. Such Babassu-based films would be environmentally friendly and cost-effective at the same time.

Moisture Transport Process in Vegetable Fiber Composites: Theory and Analysis for Technological Applications

This chapter provides theoretical and experimental information about water absorption in unsaturated polyester polymer composites reinforced with vegetable fibers. The use of raw materials from renewable sources, such as natural fibers, has shown great promise in a variety of engineering applications. Composites reinforced with natural fibers are sensitive to influences from environmental agents such as water and temperature. The organic nature of vegetable fibers is responsible for the higher moisture sensitivity of the mechanical properties of natural fiber reinforced composites when compared to synthetic fiber reinforced composites. Here, topics related to theory, experiments, mathematical modeling and numerical procedures, and technological applications for different natural fibers are presented and discussed in detail. Results of microscopy, water absorption kinetics, moisture content distribution, and area/volume relationships for unsaturated polyester composites reinforced with caroa and macambira vegetable fibers are shown and analyzed. The knowledge of moisture distribution allows the determination of areas that may show delamination problems (moisture induced degradation) due to the weakness of the fiber-matrix interface and consequently reduction in the composites mechanical properties.

The Effect of Polystyrene on the Crystallization of Poly(3-hydroxybutyrate)

Mechanical properties, morphology and nonisothermal crystallization of poly(3-hydroxybutyrate) (PHB) and blends of PHB and polystyrene (PS) were studied by tensile tests, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). A two-phase structure composed by a PHB matrix and nearly spherical particles of PS was clearly noticed in SEM images. The presence of small amounts (0.5% to 3%) of amorphous PS affected the crystallinity of PHB, being more evident when high cooling rates were applied. The kinetics of nonisothermal crystallization was modeled according to Ozawa equation. The dependence of Ozawa parameters on temperature followed the same trend for PHB and PHB/PS blends; model parameters were found to be lower for the blends than for the neat PHB.

PBAT/organoclay composite films: preparation and properties

Environmental problems caused by the increased waste associated with short-term use of plastic materials, particularly by the food packaging industry, prompted the search for biodegradable alternatives. This contribution studied one of these alternatives, poly(butylene adipate-co-terephthalate)—PBAT, a polymer that is fully biodegradable in common landfills, compounded with a small amount of Cloisite 20A organoclay. Materials were mixed in a laboratory internal mixer and films prepared in a chill roll extruder. Results show that the presence of organoclay does not increase degradation of the polymer matrix during processing, nor affects its crystallization characteristics. However, organoclay addition significantly diminished oxygen and carbon dioxide permeability of the films, making them a very interesting alternative for the food packaging industry.

Environmental Stress Cracking of Poly(3-hydroxibutyrate) Under Contact with Sodium Hydroxide

Environmental stress cracking (ESC) is one of the most important causes of polymer premature failure, occurring when a combination of mechanical load and an aggressive fluid is applied. The phenomenon is well know by polymer producers and product designers but its mechanisms are not very well understood. Although the ESC effects of many commercial polymers are well known, this type of failure in biopolymers were not studied yet. In the current work, the stress cracking behaviour of poly(3-hydroxybutyrate) (PHB) with 4,0 and 6,2% of hydroxyvalerate (HV) was investigated in injection-moulded bars under contact with sodium hydroxide (NaOH) solutions. The experiments were conducted using two different types of stress arrangements: (i) an ordinary tensile testing and (ii) a relaxation experiment. In both situations the injection-moulded bars were exposed to the NaOH solution and some testing conditions where varied, like the cross-head speed of the tensile test and the maximum load of the relaxation arrangement. The results showed that NaOH acted as a strong stress cracking agent for PHB, causing surface cracking and reducing significantly the mechanical properties. Catastrophic failure with an extensive surface damage was also observed by photographed and scanning electron microscopy (SEM) images. The magnitude of the effects increased with decreasing crosshead speed and increasing loading level.

Nonisothermal crystallization studies of PBT/ZnO compounds

Compounds of poly(butylene terephthalate) (PBT) and zinc oxide (ZnO) with filler content between 1 and 10% were prepared in a laboratory internal mixer. The processing parameters did not damage PBT thermal stability or its molecular weight as evidenced by torque rheology. The melt crystallization of PBT/ZnO compounds was investigated by differential scanning calorimetry and their morphology by scanning electron microscopy and optical microscopy. From morphological analyses, ZnO particles are well dispersed in PBT matrix, which crystallizes in typical spherulites. The melt crystallization temperatures and maximum melt crystallization rates are almost unaffected by the filler. Equally the overall crystallinity did not show any dependence on the filler content or the cooling rate. Mo’s model was found to be suitable for a description of the melt crystallization kinetics, while Ozawa model turned out to be inadequate.

Photodegradation and Photostabilization of Poly(3-Hydroxybutyrate)

The present work is concerned with the photodegradation and photostabilization of poly(3-hydroxybutyrate) (PHB) biopolymer. Two commercial grades of PHB were investigated, containing of 4.0% and 6.2% of hydroxyvalerate (HV) comonomer, named PHB1 and PHB2, respectively. Injection moulded specimens were exposed to ultraviolet radiation (UV-A) in the laboratory for periods of up to 12 weeks and then characterized by tensile testing, surface appearance, size exclusion chromatography (SEC), and scanning electron microscopy (SEM). The exposure to UV radiation caused great damaged on the surface color, reduction of molecular size and mechanical properties. The effects were more pronounced on PHB2, probably due a lighter surface color and less packed macromolecular structure which facilitates the transmission of light throughout the samples. Specimens of PHB1 were also injected with the addition of a UV absorber and antioxidant, resulting in a higher UV stability of PHB, as shown by a low reduction in molar mass and better mechanical properties.

Caracterização de compósitos obtidos a partir de polímero biodegradável e casca de arroz utilizando duas técnicas de processamento

A adicao de fibras naturais a uma matriz de polimero biodegradavel tem sido uma alternativa para obter compositos com melhores propriedades termicas e mecânicas. Tendo em vista que as propriedades dos compositos possam ser influenciadas pelas condicoes de processamento, tipo e concentracao da fase dispersa, este trabalho teve como objetivo obter compositos a partir de uma blenda comercial constituida de Poli (butileno adipato co-tereftalato) - PBAT/ Amido (EB), de carater biodegradavel, e casca de arroz (CA). Inicialmente foram preparados compositos com PBAT/Amido contendo 10,20 e 30% de (CA) utilizando extrusora de dupla rosca e misturador interno. Posteriormente, foram determinadas propriedades mecânicas e termicas dos sistemas obtidos. Os resultados das propriedades mecânicas mostraram que o modulo elastico dos compositos foi afetado pelo tipo de processamento empregado, os compositos obtidos em extrusora apresentam maior modulo que os compositos obtidos no misturador: 92% maior em compositos com 10% de carga, e 38% maior em compositos com 30% de carga. A resistencia ao impacto diminuiu significativamente e a resistencia a tracao aumentou moderadamente com o teor de casca de arroz, independente do tipo de processamento utilizado. A resistencia ao impacto de compositos com 30% de carga e aproximadamente 33% da resistencia ao impacto da blenda pura. Ja na resistencia a tracao, observou-se um aumento de 25% nos compositos com 30% de carga. Analises de MEV indicam que as particulas de carga foram adequadamente molhadas pela matriz e que a adesao carga/matriz e boa. A avaliacao dos resultados obtidos com as analises de DSC indicou que a adicao de CA nos compositos extrusados altera a temperatura de cristalizacao, variando de 75oC da amostra pura, para 101oC para as amostras com casca de arroz, resultado atribuivel ao efeito nucleante causado pela maior dispersao da carga neste tipo de processamento.