Polypropylene Lab Report

CHAPTER 5

Compatibilised Polypropylene/Organoclay Nanocompostes

Results and Discussions

Introduction

Polypropylene (PP) is one of the most commonly used polymers as food packaging [1]. Similar to other polymer materials used for food packaging, it does not have absolute barrier against various gases, water vapour,humidity and other substances [2], while food packaging industry and many other related manufacturing industry demand packaging with high barriers against the permeation of gas, moisture and flavour along with superior mechanical and thermal properties [3]. For the application of food packaging,good gas barrier property may not always neded.It is dependent on the nature of the fresh foods,e.g.vegetables,fruits,meats,etc.For fruits

The increase in tensile modulus caused by the clay loading seems to be dependent on the amount of clay in polymer matrix but same trend is observed for higher percentage of clay loading. This notion can be seen clearly in Figure 5.2 where the tensile modulus is plotted versus the clay contents. The tensile modulus for PP/clay (5%) is 170% higher than that of virgin PP. Tensile modulus expresses the stiffness of the material. The insertion of the polymer chain inside the silicate layers leads to an increase in the surface area of interaction between clay and polymer matrix, thus causing enhancement of modulus. Actually, there is a close relation between the location of the clay and mechanical properties in which the encapsulated structure show lower stiffness and higher toughness than separated structure. Obviously, it is needed good dispersion of the clay platelets, increasing surface area and high interaction between dispersed clay and matrix, to achieve a considerable improvement in mechanical properties of PP nanocomposites. The elongation at break for PP nanocomposites at various clay contents is shown in Figure 5.

Rapid decrease in weight percentage of clay filled nanocomposite is due to the burning of organic molecules present in the organoclay. The virgin PP started to decompose around 360-380oC, where as the composite started to decompose at around 390-410oC.This showed the delayed decomposition for clay filled PP. According to Ray and Okamoto2, the significant increase in the thermal stability of polymer/organoclay nanocomposites results from the exfoliated/intercalated clay platelets retarding oxygen diffusion into the polymer matrix and organic-inorganic interaction between the polymer and nanoclay. Thus improved thermal stability of the nanocomposite was attributed to its structure as well as restricted thermal motion of polymer chains in the intergallery of clay platelets. The weight loss curves in nitrogen atmosphere for filled and unfilled materials are very similar; the temperature at which the 20% weight loss takes place is only higher for the nanocomposite sample while the 50% weight loss takes place at slightly less temperature range [Table-5.3]. This is because the maleic anhydride grafted polypropylene (5%) in the nanocomposite results in clay dispersion but is also the heat source that accelerates the decomposition process. By comparing the thermal stability and weight loss of the virgin polymer and nanocomposites it is revealed that the