Polypropylene solvent cleaning

The simplest treatment is solvent cleaning [33], and the effect of dipping a polypropylene substrate into a trichloroethylene solvent vapour prior to bonding to aluminium using an epoxy adhesive is shown in Fig. 4.4. The effect of a short exposure time on the joint strength is spectacular but overtreatment... 

Photooxidation Diffusion Chemical changes due to photochemical reactions Introduction of contaminants from man-made materials, such as solvents from polyvinyl chloride (PVC) materials and PVC cement, plasticizers, and phthalates from polyethylene and polypropylene materials Protection from exposure to light, use of amber glass bottles Use of inert materials (PTFE, fiberglass-reinforced epoxy materials) steam-cleaning of groundwater well components prior to installation... 

The isolated polyether matrix was modeled using polypropylene glycol (2000 MW) and isotactic polypropylene oxide. The polypropylene glycol was degassed and placed over molecular sieves to remove residual water present in the polyol. The isotactic polypropylene oxide was isolated by repeated crystallization from acetone (9). Inherent viscosity was 1.85 in benzene (0.5% concentration) at 25°C. Films of the isotactic polypropylene oxide were cast onto glass plates (cleaned as described previously) from a 6% solution of the polymer in N,N-dimethylformamide, dried in a forced air draft oven for 1 h at 75°C, and then placed in a vacuum desiccator (0.1 mm mercury) for 24 h to insure complete removal of residual solvent. 

For polyolefins used under aggressive conditions (e.g. polypropylene fibres subject to dry-cleaning or detergent action) solvent-resistant TMP systems have been developed by covalent chemical attachment of UV stabilisers to the polymer. Two synthetic routes have been developed to do this. The first involves the modification of the polymer e.g. polypropylene) by copolymerisation with maleic anhydride to give an anhydride group in the polymer chain. This can be subsequently reacted with an alcohol or amine group in the light absorber ... 

Different plastics present different painting problems but, on the whole, once clean they do not often present problems of paint adhesion. Exceptions are the polyolefin plastics, e.g. polyethene and polypropylene. Because these polymers lack polar groups, they have low energy surfaces which are difficult to wet and are not readily penetrated by solvents. In addition to this, the surface layer of the plastic, a few nanometres thick, is often different to the bulk, being low in molecular weight and weak. Paint adhering to this layer will pull the layer away and peel off, thus appearing to have poor adhesion. 

Of course, crystalline polymers constitute many of the plastics and fibers of commerce. Polyethylene is used in films to cover dry-cleaned clothes, and as water and solvent containers (e.g., wash bottles). Polypropylene makes a highly extensible rope, finding particularly important applications in the marine industry. Polyamides (nylons) and polyesters are used as both plastics and fibers. Their use in clothing is world famous. Cellulose, mentioned above, is used in clothing in both its native state (cotton) and its regenerated state (rayon). The film is called cellophane. 

Caution Some plastic tubing, including polyvinylchloride (PVC), may have its plasticizer extracted by the solvent and deposited on the surface being cleaned. For this same reason, rubber, neoprene, and nylon tubing should not be used with these solvents when cleaning oxygen equipment. Polyethylene, polypropylene, and polytetrafluoroethylene (PTFE) tubing are satisfactory with the frequently used solvents. 

Table 4.5 Wettability of untreated and solvent-vapour cleaned polypropylene...

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