Polypropylene surface after exposure

Figure 7. Scanning electron microscope photograph of polypropylene surface after 1-h exposure to flowing blood at 200 mL/min and rod rotation...

Modifications of polymer surfaces by exposure to electrical plasmas and discharges have also been subjected to XPS examination in several recent articles (4, , 7). An example is the plasma oxidation of polyethylene, polypropylene and polystyrene in a radiofrequency inductively coupled system ( ). Figure 14 shows the Cls and 01s spectra of a polyethylene film after... 

Fig. 8 Surface of polypropylene bar after 80 weeks of UV exposure followed by uniaxial tensile test. Bar axis is vertical. Cracks formed in degraded layer, perpendicular to stress axis. Degraded surface is very fragile and easily parted from underlying material that is less degraded. Degradation tends to be greatest nearer to the corner, possibly because oxygen can diffuse into the surface layers from two adjacent surfaces. (Courtesy of T.J. Turton. See also Refs. ". )...

R.S. Bisht, R. Kumar, N. Thaku, Change in surface free energy and surface resistivity of polycarbonate and polypropylene sheets after plasma exposure. Optoelectton. Adv. Mater. 4, 144-147 (2010)... 

Derieth et al. (2008) immersed injection-molded polypropylene-bonded and PPS-based compression-molded composite bipolar plates. The authors exposed some sets of composite bipolar plates to different liquids (10 per investigation). Deviations in weight, thickness, surface topography, and electrical as well as mechanical properties were determined before and after exposure. Furthermore, to identify leachant ionic and organic species, the liquids were analyzed. 

A purely physical approach based on an entrapment procedure was developed by Guo and Ulbricht (2011) to fabricate thermo-responsive polypropylene membranes. The polypropylene surface was exposed to solutions of an amphiphilic block copolymer of polyNiPAAm (PNiPAAm) with a hydrophobic poly(butylacrylate) block. After treatment under optimised conditions (i.e., solvent, concentration, temperature, exposure time), a hydrophilisation as well as a switchable wettability were achieved. 

Fig. 3 Scission and crosslinking concentrations produced in polypropylene after 16 weeks and 34 weeks of UV exposure in the laboratory. Samples taken at different depths from the exposed surface. Each sample was 0.1 mm deep the corresponding result is plotted at the midpoint of the layer. (More details in Shyichuk, A.V. Turton, T.J. White, J.R. Syrotynska, I.D. Different degradability of two similar polypropylenes as revealed by macromolecule scission and cross-linking. Polym. Degrad. Stab. 2004, 86, 377-383.)...

Natural fiber-reinforced polyolefins are commonly apphed to automotive and constmction applications. The most abundantly used additive is fire retardant. Flammability is an important factor that often limits the application of composites to a specified field. Magnesium hydroxide is the most common flame retardant material used in the constmction industry. This filler responds well to surface modifiers and decomposes by an endofliermic reaction that releases water at temperatures close to the polymer degradation temperature as show in Eq. 6.1. Rothon et al. [78] studied the effects of magnesium hydroxide on polypropylene as a flame retarder of 60 % by weight. The smdy found less heat emission at 100 kWm after 6 min of fire exposure compared to filled PP without Mg(OH)2 at 500 kWm. ... 

Garnish and Haskins found that exposure of polypropylene to trichloroethylene vapour for 10 s resulted in a sixfold increase in joint strength using an Epoxide adhesives. The authors concluded that the improved adhesion was due to the removal of a weak boundary layer. However, the treatment causes the formation of a very porous surface, and an alternative explanation for the improved adhesion is the mechanical keying of the adhesive into the porous surface (see Mechanical theory of adhesion). Garnish and Haskins found that the optimum treatment time was about 10 s and that after 25 s the adhesion level was similar to that of the untreated polymer. This reduction is probably due to weakening of the surface region of the polypropylene. 

Figure 1 Cracks formed in the surface of polypropylene samples during tensile testing after (a) weathering for 12 weeks in Jeddah, and (b) after 4 weeks laboratory ultraviolet exposure while held in bending. (See Qayyum, M.M. and White, J.R. (1993) Polym. Degrad. Stab. 41,163 and Tong, L. and White, J.R. (1996) Polym. Degrad. Stab. 53, 381).

At room temperature, polymers appear to be inert toward nitrogen trifluoride. Samples of polyethylene, polypropylene, polystyrene, or poly-a-methylstyrene exposed for 6 d to 5 atm of NF3 at 135°C showed a mild surface reaction. After six weeks of exposure to 10 atm at 150°C,... 

Polypropylene is intrinsically less resistant to ultraviolet radiation. Although polypropylene shows powdering rather than grass surface grazing after sunlight exposure, minute surface cracks are visible under the microscope. Under certain conditions the microcracks can act as points of stress concentration. This can reduce the impact strength of the component. 

With either low-density polyethylene or polypropylene exposure to ultraviolet light under conditions of stress, after 1.5 years exposure was observed only with the unpigmented polymers the pigmented materials are free of the surface-crazing marks exhibited by polymers not containing carbon black. 

The behavior of two polypropylene nanocomposites when immersed in distilled water or sea water at four different temperatures was studied and compared with that of neat PP. The nanocomposites showed a higher water diffusion rate and equilibrium moisture content. Nevertheless, because of their superior initial mechanical properties, after 42 days exposure they were still equivalent to unexposed PP. X-ray diffraction and infrared spectroscopy were applied to characterize the surfaces of the exposed specimens. 

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