Polyethylene surface tension

Wetting is not a reciprocal property [79] in that if A spreads on B, B does not necessarily spread on A. An example of this is that a liquid epoxide resin will not spread on polyethylene, but if the resin is cured it will then be wetted by molten polyethylene. Surface tensions of epoxides are about 44 mNm" and that of polyethylene is about 30 mN m . A solid can force liquids of lower, but not higher surface tension to wet it. 

Raney K, Benton W, Miller CA (1987) Optimum detergency conditions with nonionic siufactants II. Effect of hydrophobic additives. J Colloid Interface Sci 119 539-549 Rosen MJ, Wu Y (2001) Superspreading of trisiloxane surfactant mixtures on hydrophobic siufaces 1. Interfacial adsorption of aqueous trisiloxane surfactant -M-alkyl pyrrolidinone mixtures on polyethylene. Langmuir 17 7296-7305 Stevens PJG, Kimberely MO, Mimphy DS, Policello GA (1993) Adhesion of spray droplets to foliage - the role of dynamic surface tension and advantages of organosil-icone surfactants. Pesticide Sci 38 237-245... 

Zisman discovered that there is a critical surface tension characteristic of low-energy solids, such as plastics and waxes. Liquids ihat have a lower surface tension than the solid will spread on that solid, while liquids with a higher surface tension will not spread. Examples of critical surface tension values for plastic solids in dynes per cm are "Teflon/ 18 polyethylene, 31 polyethylene terephthalate, 43 and nylon, 42-46. As one indication of the way this information can be used in practical applications, one can consider the bonding of nylon to polyethylene. If nylon were applied as a melt to polyethylene, it would not wet the lower-energy polyethylene surface and adhesion would be poor. However, molten polyethylene would spread readily over solid nylon to provide a strong bond. 

Figures 7.18(b) and 7.18(c) show the breakup into droplets of an extended filament of high density polyethylene in a polystyrene matrix. In Fig. 7.18(b) the distance between the extruder die and the quenching bath is short and the fiber freezes before breaking up, whereas in Fig. 7.18(c) the distance was increased, giving the filaments sufficient time for breakup. As the filament extends, its diameter is reduced until shear forces no longer dominate the surface tension cohesive forces and the filaments breaks into droplets, just like a stream of water from a faucet breaks up into droplets.

Here, again, we start from compressible SCFT formalism described in Section 2.2 and consider a model system in which bulk polymer consists of "free" matrix chains (Ny= 300) and "active" one-sticker chains (Na= 100). Flory-Huggins interaction parameters between various species are summarized in Table 1. This corresponds to the scenario in which surfactants, matrix chains, and functionalized chains are all hydrocarbon molecules (e.g., surfactant is a C12 linear chain, matrix is a 100,000 Da molecular weight polyethylene, and functionalized chain is a shorter polyethylene molecule with one grafted maleic group). The nonzero interaction parameter between voids and hydrocarbon monomers reflects the nonzero surface tension of polyethylene. The interaction parameter between the clay surface and the hydrocarbon monomers, Xac= 10 (a = G, F, A), reflects a very strong incompatibility between the nonpolar polymers and... 

Kollicoat IR is a unique polymer for pharmaceutical applications prepared by a graft polymerization process of polyethylene glycol (25%) with polyvinyl alcohol (75%). Kollicoat IR dissolves quickly in water and aqueous solutions of acid and alkali and reduces the surface tension of aqueous solutions to allow the solutions to have high spray rates. The polymer film is very flexible, not tacky, and easily colored. The polymer can be used as instant release coating, pore former, binder, protective colloid, etc. 

Fig. 5 Photosulfonation of LDPE. Surface tension y versus UV irradiation time for non-crosslinked ( ) and crosslinked (A) polyethylene...

Most common adhesive liquids readily wet clean metal surfaces, ceramic surfaces, and many high-energy polymeric surfaces. However, epoxy adhesives do not wet low-energy surfaces such as polyethylene and fluorocarbons. The fact that good wetting requires the adhesive to have a lower surface tension than the substrate explains why organic adhesives, such as epoxies, have excellent adhesion to metals, but offer weak adhesion on many untreated polymeric substrates, such as polyethylene, polypropylene, and the fluorocarbons. 

To obtain a usable adhesive bond with polyolefins, the surface must be treated. A number of surface preparation methods, including flame, chemical, plasma, and primer treatments, are in use. Figure 16.4 illustrates the epoxy adhesive strength improvements that can be made by using various prebond surface treatments to change the critical surface tension of polyethylene. 

Cryo- and Lyoprotectants and Bulking Agents Various mechanisms are proposed to explain why excipients serve as cryo- or lyoprotectants. The most widely accepted mechanism to explain the action of cryoprotection is the preferential exclusion mechanism [177]. Excipients that will stabilize proteins against the effects of freezing do so by not associating with the surface of the protein. Such excipients actually increase the surface tension of water and induce preferential hydration of the protein. Examples of solutes that serve as cryoprotectants by this mechanism include amino acids, polyols, sugars, and polyethylene glycol. 

Microscopic foam films have been used to study the steric interaction between two liquid/gas interfaces [130]. Two ABA triblock copolymers of the Synperonic PE series were employed P85 and F108. These commercial non-ionic surfactant were used as obtained from ICI Surfactants, Witton, UK. Blocks A are hydrophilic polyethylene oxide (PEO) chains, while block B is a hydrophobic polypropylene oxide (PPO) chain. The molecular masses and average EO contents are known from the manufacturer and yield approximate chemical formulae (Table 3.3). Data about the surface tension of electrolyte-free aqueous copolymer solutions can be seen in Fig. 3.31 [130]. It was additionally checked that NaCl (up to 510 2 mol dm 3) had no influence on these values. 

Clean, flat, homogeneous surfaces can be obtained in the laboratory, but otfly with difficulty. You must expect all surfaces around you to be rough and contaminated. So don t expect accurate results from amateur experiments on surface phenomena. The cleanest surfaces around tend to be those of low surface-tension materials such as Teflon and polyethylene films. High-tension surfaces are always contaminated, if only by water adsorbed from air. Clean aluminium foil is perhaps as close as you can get. You often get best results with a little tapping or vibration as this reduces the difference between the two angles. 

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