A associação da celulose bacteriana com outros polímeros pode ser um método efetivo para aumentar suas características e estrutura, proporcionando novas aplicações industriais. O objetivo do trabalho foi verificar a influência da celulose bacteriana nas propriedades físicas, químicas e de barreira em filmes a partir de blendas de celulose bacteriana e fécula de batata. Os filmes foram produzidos segundo planejamento de mistura ternária, tendo como variáveis independentes a celulose bacteriana, fécula de batata e glicerol. Blendas com maiores concentrações de celulose bacteriana apresentaram aumento na espessura, gramatura, taxa de permeabilidade ao vapor de água e permeabilidade ao vapor de água e, redução da densidade, solubilidade, opacidade, índice de intumescimento em pH 1,8 e 8,0 (1, 10, 30 e 60 minuto). A microscopia eletrônica de varredura mostrou filmes com matriz coesa, porém irregular com presença de partículas insolúveis de celulose bacteriana. O filme de celulose bacteriana pura apresentou aumento na gramatura, opacidade, taxa de permeabilidade ao vapor de água e no intumescimento em pH 1,8 1 minuto e pH 8,0 1, 10, 30 e 60 minutos. A celulose bacteriana promoveu elevada capacidade de retenção, absorção e baixa dessorção a água, proporcionando biofilmes com características de barreira à luz e manutenção da umidade.

The association of bacterial cellulose with other polymers can be an effective method for increasing its characteristics and structure, providing new industrial applications. The purpose of this paper was to verify the influence from bacterial cellulose in the physical, chemical and barrier properties in films of bacterial cellulose blends and potato starch. The films were made according to a ternary mix planning, with bacterial cellulose, potato starch and glycerol as independent variables. Blends with higher concentrations of bacterial cellulose exhibited increase in thickness, weight, permeability rate of water steam and permeability to water steam and reduction of density, solubility, opacity, swelling index at pH 1.8 and 8.0 (1, 10, 30 and 60 minutes). The scanning electron microscopy showed films with cohesive matrix, but with irregular morphology, containing insoluble particles of bacterial cellulose. The pure bacterial cellulose film showed increased weight, opacity, permeability rate of water steam and at swelling at pH 1.8 at 1 minute and pH 8.0 at 1, 10, 30 and 60 minutes. The bacterial cellulose contributed to high capacity of retention, absorption and low water desorption, providing biofilms that acted as barrier for light and kept the humidity constant.

Numerous studies have focused on polymer mixtures aimed at the potential applications of these materials. This work analyzed the effect of polymer reprocessing and the type and concentration of compatibilizer on the isothermal crystallization kinetics of polypropylene/wood flour composites. The composites, which were polypropylene grafted with acrylic acid (PP-g-AA) and maleic anhydride (PP-g-MA), were processed in a twin screw extruder with and without compatibilizer. Reprocessed polypropylene reached complete crystallization in less time than the composites with virgin polypropylene. The addition of wood flour to the composites did not change the kinetics significantly compared to that of the pure polymers, but the compatibilizers did, particularly PP-g-AA. The nucleation exponent (n) and crystallization rate (K) were calculated from Avrami plots. The values of n ranged from 2 to 3, indicating instantaneous to sporadic nucleation. The crystallization half-time of reprocessed polypropylene was shorter than that of virgin polypropylene and of the compositions containing PP-g-AA compatibilizer. The activation energy of crystallization and the equilibrium melting temperature were calculated, respectively, from Arrhenius and Hoffman-Weeks plots. Both of these parameters showed lower values in the composites, particularly in the ones containing compatibilizers.

In recent years, the interest in polymer recycling has increased. However, in every reprocessing step the material undergoes shear stress and is affected by temperature and oxygen. The aim of this paper is to investigate the influence of multiple extrusion in the generation of functional groups, namely hydroperoxide, carbonyl, and transvinylene. Low density polyethylene was reprocessed three times in a single screw extruder. In each recycling step hot pressed films were prepared. These films were submitted to a heat treatment in an oven with air circulation and renovation to proceed with aging tests at different times and temperatures. The results obtained showed that all functional groups had their concentration increased with the increase in number of reprocessing, the aging time and temperature of the heat treatment. The factorial design was applied to verify the influence of these parameters. All the parameters had significant effects, since their regression coefficients had the same order of magnitude, with the most influential parameter being the aging temperature, followed by the aging time and number of extrusions. Most of the interactions were influential, indicating that the formation of functional groups depends upon their interaction, and not only on their isolated effects.

Acetylation was performed to reduce the polarity of wood and increase its compatibility with polymer matrices for the production of composites. These reactions were performed first as a function of acetic acid and anhydride concentration in a mixture catalyzed by sulfuric acid. A concentration of 50%/50% (v/v) of acetic acid and anhydride was found to produced the highest conversion rate between the functional groups. After these reactions, the kinetics were investigated by varying times and temperatures using a 3² factorial design, and showed time was the most relevant parameter in determining the conversion of hydroxyl into carbonyl groups.

Residence time distribution (RTD) is a very important parameter in extrusion, either for simple polymer processing or for special processes like compounding, blending, reactive compatibilization, and controlled degradation. This work deals with the values of mean residence time (t n) as a function of the number of 45 degrees kneading elements in the screw profile, screw speed, and feeding rate. The t n values were calculated from the RTD curves, which in turn were determined by the technique of a marker added as a pulse in the steady state polymer flow. The values of t n were empirically modeled as a function of those parameters. The results showed that feeding rate is the most influent parameter, followed by number of kneading elements and screw speed. The modeling has given a quadratic function relating t n and the operational parameters tested.