Polypropylene acid enhancement

A theory for this acid effect has been developed essentially from the wool and cellulose work (3,4). Recently, in a brief communication, we reported analogous acid enhancement effects in the radiation grafting of monomers such as styrene in methanol to nonpolar synthetic backbone polymers like polypropylene and polyethylene (5). In the present work, detailed studies of this acid enhancement effect are discussed for the radiation grafting of styrene in various solvents to polyethylene. The results are fundamentally important since most of the experiments reported here have been performed in solvents such as the low molecular weight alcohols which, unlike cellulose and wool systems, do not swell polyethylene. 

Table Comparison of Cellulose with Polypropylene as Trunk Polymers for Acid Enhancement in Radiation Grafting of Styrene in Methanol...

AM Adur, S Flynn. Performance Enhancement in Talc-Filled Polypropylene Obtained by Addition of Acrylic Acid Modified Polypropylene. ANTEC, 1987, pp. 508-513. 

The inclusion of divinylbenzene (DVB) enhances the radiation grafting of styrene in methanol to polypropylene (Figure 7) especially at concentrations above 30% monomer where there is generally a 100% increase in yield. Compared with acid and neutral solutions, the Trommsdorff peak in the DVB solution has moved slightly to higher monomer concentration for polypropylene grafting. The acid enhancement is greater than the DVB effect at monomer concentrations lower than 30%, but the reverse holds above this styrene level with polypropylene. 

The radiation grafting properties of polypropylene using styrene in methanol as monomer system have been compared with those of the natural materials, cellulose and leather. Of the three, polypropylene is the most reactive trunk polymer (Table 2). Cellulose and leather exhibit comparable styrene grafting properties and all three trunk polymers show acid enhancement in copolymerisation especially in the 20-40% monomer concentration region. The polypropylene and cellulose data illustrate the... 

Long-chain aUphatic acids such as adipic acid (qv) [124-04-9] are generally used to improve flexibiUty and enhance impact properties, demonstrating subtle improvements over resins modified with the ether glycols (diethylene glycol) and polyether glycols (polypropylene glycol) (see PoLYETHERs). 

Homopolymerisation which accompanies copolymerisation increases at higher styrene concentrations, thus the grafting efficiency decreases with increasing styrene concentration (Table V). These results are similar to analogous data for polypropylene (5, 6). Inclusion of mineral acid increases homopolymerisation, however not to the same degree as it enhances copolymerisation, thus, overall, grafting efficiency is significantly improved in the presence of acid. 

Polyesters make tough and wear-resistant urethanes. The one major drawback is the hydrolysis at the ester grouping. The hydrolysis can either be acid or alkali promoted. In more neutral conditions, the major breakdown product is normally adipic acid that catalyses further attack. The normal approach is to use carbodiimides to block further breakdown. Polyols made using polypropylene carbonate produce polyurethanes with polyester characteristics but with enhanced hydrolysis resistance. 

Studies on photografting appear to have declined in interest. The presence of acid has been found to enhance the photografting of styrene onto polypropylene and cellulose with dimylbenzene giving good synergism. Both methyl methacrylate and methacrylic acid... 

A carbon black addition above a percolation threshold of 5 vol% increases the conductivity until a plateau is reached at 20 vol%. " As the level increases above 10 vol%, the viscosity of the filled polypropylene increases rapidly (see Figure 9.9). As with polyethylene, carbon black is preferentially contained in one phase of a two phase blend."" This phenomenon is used in practice to lower the concentration of carbon black required for a certain level of conductivity. Here, again, carbon black is concentrated in the preferred location. Carbon black and copper powder were used to improve connectivity of YBaCuO in ceramic superconductors. "" Dispersion of copper particles and the related changes in conductivity were enhanced by the presence of acrylic acid modifier. ... 

In preliminary work (19), divinylbenzene (DVB) has been reported to be a useful additive for enhancing the above grafting reactions. These early data (19) indicate that there are possible common mechanistic pathways between the acid effect and the DVB process. More detailed DVB studies are discussed in this paper for enhancing the radiation grafting yields of styrene in methanol to films of polyethylene and polypropylene. The work has been extended to include the use of other polyfunctional monomers such as tri-methylol propane triacrylate (TMPTA) as additives. The possibility of being able to use these additives for copolymerisation of monomers to naturally occurring trunk polymers such as cellulose will also be considered. 

The optimum in the copolymerisation process occurs at 50% monomer concentration with both additives. The behaviour of sulfuric acid in these reactions is representative of the most reactive of the mineral acids (12). A comparison of TMPTA with H SO (0.2 M) also indicates that similar trends in enhancement in radiation grafting to polyethylene film are observed with both additives (Table III). Again, when polypropylene film is used as backbone polymer (Table IV), acid and DVB show similar increases in grafting yield with styrene in methanol, however in this system, it is interesting to note that the concentration of monomer at the position of the Trommsdorff peak does not vary for neutral and acidified grafting solutions but changes from 30% to 35% when DVB is additive. 

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