LMWOM

Natural waters also contain a wide range of low-molecular-weight organic molecules (LMWOM), which are regarded as products of the microbial decomposition of, primarily, plant matter some have even been used as identifiers for certain genera of decomposers.123124... 

The formation of LMWOM is associated with reaction of O atoms and O3 molecules [17,31,32], with the alkoxy functional group being the main precursor to LMWOM formation. This, coupled with the chemistry effects of flame impingement discussed in the previous section, suggests that it is unlikely that the alkoxy functional group is a dominant surface oxidized species in the flame treatment process [17,20,31,32]. 

The formation of a layer of low molecular weight, oxidized material (LMWOM) on the surface of PP and PET films after CDT is widely accepted [10]. It is the effect of the material on adhesion that is debated. The formation of a weak boundary layer may be beneficial or detrimental to adhesion, depending on its solubility in the adhesive matrix. If the layer is soluble in the matrix, no decrease in adhesion may be observed. If, however, the layer is not soluble, this may reduce adhesion due to the presence of this cohesively weak layer at the interface. Water washing experiments were carried out to evaluate the effect of LMWOM on the surface chemistry and morphology. XPS and AFM... 

Corona discharge treatment in air proceeds through surface oxidation, which is accompanied by considerable chain scission leading to the formation of water-soluble low molecular weight oxidized material (LMWOM). 

As shown in Table 20.1, corona discharges are dominated by 0-atom reactions involving, for example, atomic oxygen and ozone that lead to scission of the PP chains and the formation of water-soluble LMWOM. The extensive chain scission associated with corona processes affects the wettability and stability of the treated-PP films. By contrast, as shown in Table 20.1, flame-surface oxidations are dominated by OH radical reactions that lead to oxidation without LMWOM formation. The more limited chain scission associated with flame treatment leads to formation of more polar groups on the PP surface. Due to the lack of LMWOM formation, it was concluded the flame-treated PP is more highly oxidized after washing with water, more wettable, and more stable than corona-treated PP [103]. 

---