Cellulose acid enhancement, radiation

Comparison of Cellulose with Other Backbone Polymers (Wool, Polyethylene, Polypropylene and PVC) for Acid Enhanced Radiation Grafting of Styrene in Methanol... 

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. 

Acid enhancement in the radiation grafting of styrene in methanol to cellulose (4), wool (3) and in preliminary work with the polyolefins (5 6) has been proposed as being predominantly due to such reactions. 

Further work on the mechanism of the acid enhancement in both UV and gamma ray grafting is reported. The copolymerisation of styrene in methanol and dioxan to cellulose is used as model system. Acid enhances grafting and homopolymer formation in both radiation systems. Analysis of the homopolymer from the grafting runs indicates that acid reduces the chain length, but increases the numbers, of grafted chains. 

Effect of Acid as an Additive on UV and Radiation Grafting. Previous studies have shown that mineral acids can enhance the radiation grafting of styrene to cellulose under certain radiation conditions. W The results of analogous experiments in photografting are shown in Table III, and compared with the corresponding gamma ray data. In... 

Mechanistically the role of acid In enhancing gamma radiation copolymerization Involves a number of competing processes. In previous work In this field with cellulose (i6), it has been suggested that acid at the concentrations used does not markedly affect the precipitation of the grafted chains or the swelling of the backbone polymer, especially with cellulose. Instead It has been proposed that part of the acid enhancement can be attributed to a radiation chemistry phenomenon Involving increased G(H) yields and thermallzed electrons (Equations 7 to 9). These processes can lead... 

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... 

When the source of initiation is altered from ionising radiation to UV, analogous additive effects to those previously discussed have been found. For reasonable rates of reaction, sensitisers such as benzoin ethyl ether (B) are required in these UV processes. Thus inclusion of mineral acid or lithium perchlorate in the monomer solution leads to enhancement in the photografting of styrene in methanol to polyethylene or cellulose (Table V). Lithium nitrate is almost as effective as lithium perchlorate as salt additive in these reactions (Table VI), hence the salt additive effect is independent of the anion in this instance. When TMPTA is included with mineral acid in the monomer solution, synergistic effects with the photografting of styrene in methanol to polyethylene are observed (Table VII) consistent with the analogous ionising radiation system. 

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. 

Recently a method was reported for enhancing the radiation grafting of monomers to polymers by the simple addition of mineral acid to the grafting solution >Under some experimental conditions organic acids act in the same manner >. Extensive work on this acid effect has been published for the radiation copolymerisation of styrene to cellulose wool, the polyolefins >PVC and polyesters. The acid effect has also been extended to the grafting of monomers other then... 

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