Polypropylene surface tension

Analysis of the Non Metallized. Pretreated Polypropylene. In a previous paper (1), we have shown that for very short treatment times (23 ms) in N2 or NH3 plasma, the first observed effect of the plasma was an increase of the dispersive component (y ) of the polypropylene surface tension. Since almost no nitrogen nor oxygen were detected by XPS for treatment times shorter than 0.7 s, it was concluded that the plasma had first a physical effect rather than a chemical one, although the efficiency of the treatment on the Al-PP adhesion was high (as proven by the use of a scotch-tape test). 

Recently developed blood oxygenators are disposable, used only once, and can be presterilized and coated with anticoagulant (e.g., heparin) when they are constructed. Normally, membranes with high gas permeabilities, such as silicone rubber membranes, are used. In the case of microporous membranes, which are also used widely, the membrane materials themselves are not gas permeable, but gas-liquid interfaces are formed in the pores of the membrane. The blood does not leak from the pores for at least several hours, due to its surface tension. Composite membranes consisting of microporous polypropylene and silicone rubber have also been developed. 

Polypropylene exhibits all the characteristics noted above—it is chemically inert, resistant to solvents, and has low surface tension—yet is being used in... 

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. 

Polypropylene, in particular, has a very low surface tension (less than 32 dynes/cm2). Because of the low surface tension, it is very difficult to wet out and because of the apolar nature of the polypropylene backbone, it is a very difficult material to adhere to. Therefore, copolymers of ethylene propylene diene monomers (EPDM) with polypropylene have been developed. The higher the level of... 

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. 

Best surfactant behaviour was achieved in the case of the polyether trimethylsilane by introducing a hexyl spacer group in the molecule structure. For testing the wetting ability a droplet (50 pi) of an aqueous surfactant solution is applied by syringe to a clean sheet of polypropylene. Afterwards the increase of the diameter of the droplet is measured. The surface tension of the aqueous solution is usually determined by the well known ring method of du Nouy [5]. 

For a hydrophobic porous material with contact angle greater than 90°, the APc is >0 and depends on the liquid surface tension and the membrane pore size. As an example, considering water-air-polypropylene system, one can calculate that for a dry membrane with a pore size of 0.03 pim (30 nm) the critical entry pressure of water is more than 300 psi (>20 bar). 

It has generally been observed that urethane systems, which are cured on the surface of some low energy materials, are also free from adhering to them, i.e. they are self-releasing. Materials which show this characteristic relative to urethanes in a very effective way include at least three different types of plastics polytetrafluoroethylene, polyethylene, and polypropylene. These materials all have a defined critical surface tension sc less than about 30 dynes/cm. Assuming that this value is near, the liquid vapor surface tension lv value of an effective IMR urethane systems, then the work of adhesion as given by Equation 4 is as follows ... 

Two common liquid membrane support materials, polytetrafluoroethylene and polypropylene, have critical surface tensions of 18 mN/m and 35 mN/m, respectively. Manufacturers often supply critical surface tensions for their porous films. Liquids with a surface tension, y, less than the critical surface tension will probably wet the surface. Therefore, hydrocarbons will wet polypropylene, but water (y = 72 mN/m) will not. Shafrin and Zisman (30) have summarized critical surface tension data for many materials and correlated the data such that critical surface tensions may be estimated from knowledge of the functional groups in the chemical structure of the surface. 

In principle such complete wetting, as just discussed for PS/PVME blends, could also occur in immiscible blends when spreading of the melt with the lower surface tension is possible. The immiscible blend of polystyrene (PS) and polypropylene (PP) does not show this wetting behavior (Figure 5). We observe ... 

Whereas the surface tension of RME is reduced in an appropriate way only by the slighdy cholesterol-modified and the alkyl-modified silicone, all three compounds have an excellent ability to increase the spreading of RME on polypropylene. In general these two properties are closely related [7]. 

Chemical or physical surface treatments are especially required for structural bonding of low-surface-energy plastics. Low-surface-energy plastics include polyethylene, polypropylene, TPO, and fluorinated polymers. These surface treatments are designed to increase the critical surface tension and improve wetting and adhesion. In addition to increasing the critical surface tension, surface treatments are designed to remove contaminants or weak boundary layers, such as a mold release. 

Stress depressions (Ao) of hard elastic polypropylene, hard elastic high impact polystyrene, and Gore-Tex , a nonelastic, porous. Teflon material were measured when these polymers, under load, were subjected to changes in their environment from air to various nonswelling liquids. The stress depressions were studied as a function of liquid surface tension and viscosity and the strain imposed on the materials. 

In this study, we closely examine the stress depression phenomenon as a function of environmental surface tension, strain, and viscosity. These results are correlated with changes in the void content as the specimens are strained. Three systems are investigated hard elastic HIPS, hard elastic polypropylene and Gore-Tex, a non-elastic (see Figure 5) but fibrillated Teflon material (see micrograph in Figure 2c). 

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