Plastics, non-polar

Non-polar plastics such as polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), and polystyrene (PS) are more difficult to adhere to. 1,3-butylene glycol diacrylate has shown some efficiency in promoting adhesion to these types of substrates. 

Along with this, plastification induces growth of highly elastic deformations on the background of reduced elasticity modulus and other strength characteristics of the polymer materials [103]. Impairment of breaking strength under tension of LDPE-based films takes place as the concentration of the non-polar plasticizer bis-(2-ethylhexyl)sebacate increases. The decrease in 06 reaches 25% at PI concentration of about 20 wt% [5,6]. 

At the identical values of ( )2 and strain rate, the smaller influence of a non-polar plasticizer (transformer oil) on a physical network of PDUE in comparison with DOS and TBP corresponds to the smaller deviation of stress-strain dependence (Figures 10.63, 10.64, soUd lines). 

The non-polar plasticizer (TO) influences the physical network of PBU-2 to a smaller extent than DBCF and TBP. The influence on mechatucal properties of proton accepting plasticizers (DBCF and TBP) (Figures 10.72 and 10.73) is similar. A similar behavior was observed for PDUE samples (Figures 10.63 and 10.64) as well. 

Plasticizer ability to rapture the labile physical network is clearly demorrstrated by mechanical properties of PBU-2 samples plasticized by TO, DBCF and TBP (Figtrre 10.71b). At the same volume fraction of the plasticizer, ( )j, the critical strain, 8, of PBU-2, swollen in non-polar plasticizer TO, is higher than the 8 values of samples, swollen in plasticizers which are proton acceptors such as DBCF and TBP. 

Not only can the water molecule pass through gaps in the network because of its small size, but also because it is compatible with (i.e. effectively soluble in) the polymer. Thus polar adhesives are naturally hydrophilic whereas non-polar plastics, such as PVC and Polythene, are not i.e. like permeates like . The solubility of water in epoxies is of the order of a few mass per cent, and the coefficient of diffusion of water at 20 °C is around 10 m s . 

G. G. Gonzalez, "Evaluation of Polar and Non-Polar Plastics Compounded with Thermomechanical Wood Fibers", Dissertation, Dept, of Chem. Engr., Miss. State Univ., Aug. (1979). 

The non-polar plastics are truly covalent and generally have symmetrical molecules. In these materials there are no polar dipoles present and the application of an electric field does not try to align any dipoles. The electric field does, however, move the electrons slightly in the direction of the electric field to create electron polarization , in this case the only movement is that of electrons and this is effectively instantaneous. Examples of non-polar plastics are PTFE (and many other fluoropolymers), PE, PP and PS and these materials tend to have high resistivities and low dielectric constants. 

For non-polar plastics the dielectric constant is independent of the alternating current frequency because the electron polarization is effectively instantaneous. Nonpolar plastics always have dielectric constants of less than 3. 

For non-polar plastics the electronic polarization is effectively in phase with the external field (Le., q 0 and cos q is also approximately 0) and the power factor is generally less than 0.0003. non-polar plastics suffer from very little internal friction and minimal internal heating. 

Non-polar plastics, such as the fluoropolymers, are not as affected by the water because they tend not to absorb water and temperature effects are not generally as severe because increased temperature does not affect the electronic polarization. 

Primers that enable cyanoacrylates to bond non-polar plastics and elastomers such as polyethylene, polypropylene and thermoplastic... 

If attempts are made to bond non-polar plastics such as PE, polypropylene (PP), fluoroplastics, and thermoplastic polyolefins (TPO), very weak assemblies are usually obtained with tensile shear strengths of <0.7 MPa. These readily fail under slight impact or exposure to moisture. 

The most common reason tackifiers are added is to improve the adhesion to non-polar plastics see Table 15.1. Rosin ester tackifiers added at 15-30% will normally increase the peel several fold on polyethylene and polypropylene surfaces. For more polar surfaces, terpene-phenolic or styrene-phenolics are added. Tackifiers are discussed in more detail in Sect. 15.5 below. Acrylics are compatible with only a narrow range of commercial tackifiers. Tackifier dispersions are available for water-based adhesives. 

Cyanoacrylates are typically suitable for temperatures up to 100 C, although some speciality cyanoacrylates are available for higher operating temperatures. One of the major benefits of cyanoacrylates is that they can be used (with a primer) to bond the non-polar plastics. More details about these primers are given in Section 6.2... 

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