Vapor-permeable PP membranes – Tensile properties and surface structure

This paper presents the results of identification strength tests of selected vapor-permeable membranes together with an evaluation of their surface structure before and after failure. Polypropylene three-layered membranes of randomly chosen Polish manufacturer – windproof membrane (MB) and roof membrane (MG) – were chosen for research. Both membranes are made of two layers of polypropylene fabrics, between which there is a functional layer (film), ensuring proper operation of the product. The results obtained for tensile parameters and resistance to tearing (nail shank) are within by the manufacturer’s declared values (MDV). Tensile strength of membrane MB was equal 275 ± 11 N/50 mm in machine direction (MD) and 154 ± 5 N/50 mm in transverse direction (TD) while membrane MG characterized by tensile strength 209 ± 9 N/50 mm in MD and 126 ± 4 N/50 mm in TD. Resistance to tearing was more repeatable for membrane MG – the standard deviation did not exceed 3 N. Although the resistance to tearing of membrane MB was more than three times higher, the standard deviation was 17 N on average. Resistance to tearing of membrane MB was equal 212 ± 21 N in MD and 293 ± 14 N in TD, while membrane MG characterized by resistance to tearing 66 ± 3 N in MD and 62 ± 4 N in TD. Unfortunety, in the case of the membrane MG the mass per unit area was not within the MDV range. It was equal 90 g m−2 and together with the expanded uncertainty ± 2 %, was completely outside the lower tolerance limit. Structure analysis allowed to conclude that digital images are sufficient to observe the changes occurring in the microstructure of membranes and to make a preliminary assessment of their structure before or after failure. The results presented in paper emphasize the importance of maintaining the usable features declared by manufacturers, especially mass per unit area, and of continuously monitoring the quality of materials with use of relatively simple tests at the stage of factory production control (FPC).