Masterbatch de nanocelulose para a produção de nanocompósitos de matrizes termoplásticas / Nanocellulosis masterbatch for the production of nanocomposites from thermoplastic matrices

O presente trabalho tem como objetivo a produção de masterbatch de nanocelulose para utilização na produção de nanocompósitos de matrizes termoplásticas. Um masterbatch de interesse comercial deve apresentar a característica de permitir a fácil redispersão em escala nanométrica da nanocelulose na matriz polimérica e melhora em propriedades mecânicas do produto final. Sendo assim, este trabalho visou a produção de masterbatches de nanocelulose com ECOVIO®, para utilização na produção de nanocompósitos de matrizes termoplásticas. Os masterbatches foram preparados via solução em ácido acético glacial, seguida de precipitação em água.  As amostras foram caracterizadas via análise termogravimétrica (ATG), microscopia eletrônica de varredura (MEV), calorimetria exploratória diferencial (DSC) e difração de raios-X (DRX). A caracterização por MEV mostrou que não foram observados aglomerados de nanocelulose, com a matriz revestindo as partículas da mesma. A DRX mostra os picos característicos de cada polímero, sendo que possível observar que o masterbatch nanocelulose/ECOVIO® possui picos referentes aos dois polímeros, ou seja, o revestimento das partículas de nanocelulose foi eficaz. Já a caracterização térmica evidenciou a estabilidade térmica dos masterbatches

Estudo experimental do processo de rotomoldagem de PELBD: efeitos sobre a morfologia e estabilidade dimensional Experimental study of rotational molding process of LLDPE: effects on morphology and dimensional stability

No presente estudo o empenamento de peças de polietileno linear de baixa densidade (PELBD) moldadas por rotomoldagem foi investigado. O efeito de diferentes fatores como espessura da peça, taxa de resfriamento e diâmetro de tubo de ventilação foi avaliado. Além dos experimentos de rotomoldagem, uma técnica alternativa denominada "Hot Press" foi também aplicada para investigar o empenamento de dois diferentes PELBD sob condições típicas da rotomoldagem quanto ao resfriamento assimétrico. Cristalinidade e morfologia esferulítica ao longo da espessura das peças rotomoldadas foram avaliadas por Calorimetria Exploratória Diferencial (DSC) e Microscopia Ótica de Luz Polarizada. Verificou-se que o grau de empenamento aumenta com a taxa de resfriamento. O aumento do diâmetro do tubo de ventilação é mais efetivo na redução do empenamento principalmente em menores taxas de resfriamento. Nos experimentos de "Hot Press" o PELBD com menor índice de fluidez e maior módulo de flexão apresentou menor empenamento. Nos experimentos de "Hot Press" a espessura das peças afetou o empenamento somente para maiores taxas de resfriamento. Em geral, a cristalinidade e o tamanho de esferulitos se mostraram menores nas posições ao longo da espessura das peças rotomodadas onde as taxas de resfriamento eram mais rápidas.In the present study the warpage of rotationally molded parts of a linear low density polyethylene (LLDPE) was investigated. The effect from different processing factors such as part thickness, cooling condition and diameter of the venting tube was evaluated. In addition to the rotational molding experiments, an alternative experimental technique, referred to as "Hot Press", was also applied to investigate the warpage of two different grades of LLDPE under typical rotational molding conditions, which means slow cooling from only one side. The crystallinity and spherulitic morphology along the thickness of the rotationally molded parts were studied by Differential Scanning Calorimetry and Polarized Light Optical Microscopy. It is shown that the warpage increases with increasing cooling rate. The increase in diameter of the venting tube is more effective in reducing the warpage of rotationally molded parts, especially for lower cooling rates. In hot press experiments the grade of LLDPE with lower melt flow index and higher flexural strength presented lower warpage. The part thickness affects the warpage in hot press experiments only for faster cooling rates. In general, crystallinity and spherulitic diameter are lower in positions along the cross section of the rotationally molded part where the cooling rate is faster

Determination of non-isothermal crystallization rate constant for pseudo-experimental calorimetric data

In the present work, non-isothermal crystallization data in the form of heat flow vs. temperature curves were generated using the Nakamura Model and its typical parameters reported in the literature for polypropylene. The values obtained for these curves were added to experimental baselines of a DSC to introduce typical noises in the calorimetric traces generated. The Master Curve Approach was applied by one of the authors to retrieve the non-isothermal crystallization rate constant for these simulated curves without information about the conditions used to generate these pseudo-experimental curves. Thus, the applicability of the Master Curve Approach was tested for data perfectly described by the Nakamura Model. With this procedure, the authors were able to check the sensitivity of the method to uncertainties in the determination of the induction time. The results showed good agreement between the pseudo-experimental curves and the curves simulated using the retrieved non-isothermal crystallization rate constant. However, this good agreement was only possible due to a compensation effect, because some of the parameters showed significant differences between the pseudo-experimental and retrieved values. Among these parameters are the pre-exponential factor of the non-isothermal crystallization rate constant, the temperature of the onset of the crystallization process, and the initial degree of crystallinity of the differential form of the Nakamura Model. These problems were not caused by the Master Curve Approach, but by inherent difficulties in the DSC analysis

Correlation between Surface Energy and Adhesion Force of Polyethylene/Paperboard: A Predictive Tool for Quality Control in Laminated Packaging

Poor adhesion continues to be a problem for manufacturers of laminated packaging. Therefore, the aim of this research was to study the effect of flame treatment, the type of coating, and starch application on the adhesion force of polyethylene/paperboard. The force of adhesion was determined using the peel test method; the paper surface energy was assessed by contact angle analysis; and paperboard roughness was determined by profilometer. The flame treatment did not affect the surface roughness but significantly increased the paperboard surface energy. The paperboard coated with polar latex showed much higher surface energy than the paperboard coated with nonpolar latex. The adhesion force of polyethylene presented a linear correlation to the surface energy of the paperboard. Therefore, the surface energy of paperboard is an excellent indication of its adhesion force to polyethylene, and this represents a very reliable and practical method in terms of quality control in the paper industry for producing laminated packages