Low-density polyethylene (LDPE) building films – Tensile properties and surface morphology

The paper presents results of strength tests of selected low-density polyethylene (LDPE) building films with various thicknesses, including the assessment of their surface microstructure before and after failure with the use of digital and scanning electron microscopes. Films came from one manufacturer and encompassed: vapor-proof films and construction films. A significant correlation between the film thickness and tensile strength was found only for vapor-proof films. Increasing the film thickness by 1 μm increases the tensile strength value by 0.14 MPa on average when stretching in both longitudinal (MD) and transversal (TD) directions. Furthermore, significant differences in the strain at tensile strength and strain at break for MD and TD were observed in some cases. The coefficient of variation of the strain at break of the samples, varies from ca. 2%–20% depending on the set of the samples, what caused by low mass per unit area and proves high heterogeneity of the samples and presence of local defects or lumps which affect the elongation value of the tested LDPE film sample. It was also proven that the influence of roughness parameters on tensile strength exists, and the parameters maximum height of the surface (Sz) and skewness of height distribution (Ssk) are good indicators of construction film tensile strength. The results emphasize the importance of maintaining the useable features declared by manufacturers, especially the thickness of the product, and of continuously monitoring the quality of their products with the use of relatively simple tests such as roughness measurements at the stage of factory production control (FPC).