Thais Helena Demetrio Sydenstricker

Pull-out and other evaluations in sisal-reinforced polyester biocomposites

Although sisal fibers have been used by several authors, the Brazilian variety has not yet been thoroughly characterized. In this work the surface of sisal fibers was modified by treatment with NaOH or N-isopropyl-acrylamide solutions. Lignin content and density of fibers are reduced with the chemical treatment and the N-isopropyl-acrylamide treatment causes a significant reduction in moisture absorption. Tensile tests of NaOH (0.25, 0.5, 1, 2, 5, and 10% w/w) and N-isopropyl-acrylamide (1, 2, and 3% w/w) treated fibers were carried out and a reinforcement effect of the sisal treated with 2% solutions was observed. TGA measurements showed that with the NaOH treatment the fiber becomes more thermally resistant. SEM micrographs and crystallinity index of sisal indicated how different treatments alter the fiber surface. Pull-out tests in polyester resin were performed, evidencing that all treatments were effective in improving interfacial adhesion. The best results were obtained with the 2% N-isopropyl-acrylamide treatment. The main advantages of pull-out tests is that without considering composite processing variables, good performance sisal/polyester composites may be selected before their laborious and material-consuming preparation step.

SEM studies of tensile fracture surfaces of polypropylene—sawdust composites

Composites of polypropylene (PP) or PP plus maleated polypropylene (MAPP) and sawdust coated with 22.4 wt% MAPP were prepared under fixed processing conditions (mixing temperature, rate of rotation and mixing time). The tensile properties and the fracture mechanisms of the composites have been studied. The effect of MAPP content on the properties of PP mixes were also studied. Scanning electron microscopy (SEM) was performed to analyze the tensile fracture surfaces and the interfacial fiber/matrix adhesion. The tensile properties of composites with up to 10% MAPP have not been improved by increasing MAPP content. This has been attributed to the poor filler/matrix adhesion. The addition of higher MAPP content to the PP composites produces better adhesion of sawdust to PP matrix and an increase in the tensile strength.

Evaluation of Multilayer Thermoformed Films for Food Packaging

In this work, high- and medium-barrier to oxygen films were studied. The films were thermoformed in the shape of sausage packaging, and their properties were verified before and after processing. Film characterization included evaluations of overall and individual layer thickness, crystallinity index, oxygen permeability rate, perforation strength, clarity, and brightness. Thermoforming resulted in significant modifications in thermal, mechanical, and optical properties, and the corners of the packaging were the most critical regions. After thermoforming, the oxygen permeability rate significantly increased, whereas perforation strength, clarity, and brightness were reduced, although no layer discontinuity was verified even in the corner regions.

Desempenho de filmes multicamadas em embalagens termoformadas

Flexible multilayer plastic films may be used for the thermoforming of packages for meat products. In this case, the packages must meet the technical requirements of medium or high barrier to oxygen, depending on the characteristics of the food product, in order to avoid contamination during its shelf-life and consequently risk to human health. However, the thermoforming process alters the original characteristics of the plain films, which could render them inadequate to use, especially in the deepest corners of the packages, which are the critical points. This work addressed the thermoforming effects on the properties of two multi-layered plastic films, called medium barrier (MB), comprising PP/tie/PA6/tie/PA6/tie/LDPE, and high barrier (HB), where the central adhesive (tie) layer was replaced by a layer of ethylene vinyl alcohol copolymer (EVOH). The characterization of the films included investigations of thickness, oxygen permeability, and mechanical and optical properties.