Study of processing effects on crystallinity and CO ₂ /O ₂ permeability in blow-film polypropylene- palygorskite clay composites

The present work focuses on the analysis of the effect of incorporation and dispersion of Paligorskite (Pal) clay in a polypropylene (PP) matrix on the permeability properties to different gases. The Paligorskite clay used in this study was modified with a silane coupling agent (3-aminopropyl trimethoxysilane) to improve its compatibility with the polypropylene matrix. Composites were generated using a modular twin-screw extruder at high and medium shear stresses and varying percentages of modified clay (0.5%, 1.0% and 1.5% w/w), these composites were characterized by transmission electron microscopy (TEM) to determine the degree of dispersion and distribution of the clay within the polypropylene matrix. Subsequently, the composites were used for film formation by a blown extrusion process. The films were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and permeability. Gas transport properties including helium (He), oxygen (O 2 ) and carbon dioxide (CO 2 ) were measured and analyzed. The results showed that the films with 1.0% modified palygorskite exhibited the highest degree of dispersion-distribution, generating the lowest percentage of crystallinity, as demonstrated by XRD and DSC methods. These changes induced by the incorporation of palygorskite clay increased the permeability to O 2 and CO 2 by 55% and 66%, respectively. This result is interesting since these films can potentially be used in applications such as greenhouse roofs in the agricultural field, where permeability to O 2 and CO 2 is important since these are the gases involved in the plant growth process.