Polypropylene, water permeability

An important part of the retort simulation for LEP and PEP structures is the temperature dependence of the polypropylene and polycarbonate water permeabilities. Measurements of polypropylene and polycarbonate water permeabilities were made using a MOCON Permatran-W and it was found that polycarbonate has a water permeability which decreases slightly with temperature whereas polypropylene increases with temperature. Near retort temperature the water permeabilities of both materials are similar at storage polycarbonate has a water permeability about ten times greater than polypropylene. Measurements shown in Figure 4 are in good agreement with previously reported results for polycarbonate (2,14-18) and polypropylene (5,19-11). ... 

Figure 4. Water Permeability for Polypropylene and Polycarbonate. Polypropylene measurements were made on 9.5 mil extruded sheet polycarbonate measurements were made on 10 and 20 mil extruded sheet. Note that permeability has water pressure in the denominator which is distinctly different from a WVTR (water vapor transmission rate).

A porous polypropylene membrane with a water permeability coefficient of 4.2 m/s.bar is used in membrane distillation. Calculate the pure water flux for a feed temperature of 50 C and 90°C, respectively. The temperature at the permeate (distillate) side is 20°C. Neglect temperature polarization. 

Figure 8.6 Barrier properties of commercial PHA resins compared to other bio- and oil-based polymers used for packaging, as measured by oxygen and water permeabilities, (PS1540 Polystyrene from Arkema PP7712 Polypropylene from Total Chemical Company PLA7001D Poly(lactic acid) from Natureworks P228 PHA from Biomer MirelF1006 3002 PHA from Metabolix Enmal YIOOOP PHA from Tianin Biologic PA MXD6 PHA from Mitsubishi Chemical Company).

Oilfields in the North Sea provide some of the harshest environments for polymers, coupled with a requirement for reliability. Many environmental tests have therefore been performed to demonstrate the fitness-for-purpose of the materials and the products before they are put into service. Of recent examples [33-35], a complete test rig has been set up to test 250-300 mm diameter pipes, made of steel with a polypropylene jacket for thermal insulation and corrosion protection, with a design temperature of 140 °C, internal pressures of up to 50 MPa (500 bar) and a water depth of 350 m (external pressure 3.5 MPa or 35 bar). In the test rig the oil filled pipes are maintained at 140 °C in constantly renewed sea water at a pressure of 30 bar. Tests last for 3 years and after 2 years there have been no significant changes in melt flow index or mechanical properties. A separate programme was established for the selection of materials for the internal sheath of pipelines, whose purpose is to contain the oil and protect the main steel armour windings. Environmental ageing was performed first (immersion in oil, sea water and acid) and followed by mechanical tests as well as specialised tests (rapid gas decompression, methane permeability) related to the application. Creep was measured separately. 

Water vapour polypropylene has a low permeability, roughly evaluated at 2 compared to a full range of 0.05 up to 400 for all tested plastics. 

COC has a low permeability to water vapour, inferior to that of polypropylene. 

Barrier Properties. Vinylidene chloride polymers are more impermeable to a wider variety of gases and liquids than other polymers. This is a consequence of the combination of high density and high crystallinity in the polymer. An increase in either tends to reduce permeability. A more subde factor maybe the symmetry of the polymer structure. It has been shown that both polyisobutylene and PVDC have unusually low permeabilities to water compared to their monosubstituted counterparts, polypropylene and PVC (88). The values listed in Table 8 include estimates for the completely amorphous polymers. The estimated value for highly crystalline PVDC was obtained by extrapolating data for copolymers. 

A new development reported by Li and Sirkar [141] for MD-based desalination makes use of polypropylene hollow fibers coated with a plasma polymerized sUicone-fluoropolymer. This ultrathin coating on the outside of the fiber was water vapor permeable and was instrumental in decreasing the susceptibility of the composite membrane to wetting and fouling. They reported stable water vapor fluxes between 41 and 79 kg h for runs lasting up to 400 h. 

To obtain x-ray diffusion results from swollen hydrolyzed samples, methods were developed to inhibit sample dehydration during the course of the experiment. This was achieved by sealing the samples, thermally, in a bag constructed from oriented polypropylene film. Oriented polypropylene was selected because it possesses low permeability to water and is also essentially "transparent" in the small angle x-ray scans. With such a construction, we determined that the weight of a swollen sample changed by less than 0.2% during the period required to obtain the small angle x-ray scans. 

Water vapor permeabilities for plasma formed films on polypropylene were measured using a similar method reported by Yasuda et al.(9) The water vapor permeability was calculated using the following relationship.(10)... 

A thin metallic film (1000 A, carbon-to-tin ratio less than 0.3) was deposited onto polypropylene and the permeability determined. A water vapor permeability of 1.76 X 10 cm (STP) cm cm 2 S cra Hg-l was obtained, which is of the order of values usually found for metal coatings such as copper. (Table III). 

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