Organic vapour permeability

Volatile organic -compounds Construction of passing samples with sorbent tube that fits into sample chamber fitted with a diffusional membrane permeable to organic vapours. Organics desorbed from sorbent and analysed by GC-MS [73]... 

If the polarity and structural parameters are similar for two polymers then the diffusion will be related to the degree of crystallinity, i.e. HDPE, being more crystalline than LDPE, will be less permeable to organic vapours. 

The emission of organic vapours into air is a serious environmental problem. Because of the large difference between the permeability of nitrogen (air) and those of all kinds of organic vapours (see chapter V and VT), membrane processes can be applied to recover and effect the re-use of organic vapours especially at high vapour concentrations. 

The barrier properties of PLA have not been extensively studied. The first articles treating the permeability of PLA film have been published in 1997 [120, 121], when PLA started to be considered for packaging applications. PLA films with various L/D ratios, different crystallinity degree and blends with numerous additives and polymers have been tested in recent years with gases, water vapour and organic compounds. 

Consequently, it appears that the L/D ratio of PLA influences the gas permeability but no conclusion can be reached regarding the water vapour transport in this pol)uner. Moreover, generally speaking, the crystallization of the PLA matrix makes it possible to decrease the gas permeability and the organic compound sorption in PLA. However, no agreement has been formed regarding the influence of crystallinity degree on water vapour transport in PLA due to the variety of PLA composition (L-lactic acid content) and measurement systems. 

The permeability of latex films to water and organic solvent vapours has been investigated by a number of authors [69,70], particularly Hearn and co-workers [69] in the UK. DSC and microwave spectroscopy have been used to investigate aspects of water loss from latex films [71]. 

If onh he size of the molecules is considered, it might be expected that large organic molecules in the vapour state would have low permeability coefficiraits cornpaied to simple gases. 

Eq. VI - 74 is the basic equation for liquid transport and it is the same as that for gas transpon (see eq. VI - 46) and vapour transpoit. However, due to the (high) interaction between organic liquids and polymer the permeability coefficient Pj is dependent on composition and temperature. Both solubility and diffusivity are concentration and temperature dependent as have been discussed in chapter V Eq. VI - 74 illustrates the important parameters involved, the permeabilitj coefficient is a membrane- or material-based parameter. Other parameters of interest are the effective membrane thickness I and the partial pressure difference Apj. The permeation rate is inversely proportional to the membrane thickness and proponional to the partial pressure difference across the membrane. In general eq. VI - 74 can be w ritten as... 

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