Cellulose grafting, acid effect

The inclusion of mineral acid in the grafting solution has recently been shown to increase the radiation copolymerisation yield, particularly when styrene is grafted to trunk polymers like wool (3) and cellulose (4) i.e. polymers which readily swell in polar solvents such as methanol. This acid effect is important since for many copolymerisation reactions, relatively low radiation doses are required to yield finite graft. The process is particularly valuable for monomers and/or polymers that are either radiation sensitive or require high doses of radiation to achieve the required graft. 

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 Effect in UV- and Radiation-Induced Grafting of Styrene to Cellulose... 

Recently inclusion of mineral acid in the grafting solution was found to enhance the grafting yields for a typical system such as the copolymerisation of styrene in methanol to cellulose in the presence of gamma rays (13). The acid effect now appears... 

In the present work, further mechanistic data for the acid effect in both UV and gamma radiation systems are reported, particularly molecular weight studies on the species present in the grafting solutions. The significance of these acid effects in possible commercial applications of the resulting copolymers of cellulose is also briefly mentioned. 

Mechanism of Acid Effect in Radiation Grafting. In earlier studies (13,14,15,21) on the mechanism of the acid effect on radiation grafting of styrene (MH) in dioxan or methanol (SH) to cellulose(Cell-OH)the sequence of events depicted in Equations (1) - (9) was proposed to explain the phenomenon. Thus, cellulose can undergo bond... 

Acid Effects in UV Comonomer Grafting of Methyl Methacrylate. The UV grafting of methyl methacrylate dissolved in methanol to cellulose is complicated by the degree to which competing homopolymerization occurs. The problem most often encountered is the solidification... 

Mechanism of Acid Effect in Cellulose UV Comonomer Grafting Procedure. In the earlier work (7) involving the UV grafting of monomers to cellulose, it was shown that radical sites, where copolymerization can occur, are formed in cellulose either by the direct action of UV on... 

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. 

Acid Effects in Radiation Grafting of Styrene to Cellulose and Polypropylene... 

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... 

UV grafting have also been reported, predominantly with the styrene in methanol to cellulose system The acid effect thus appears to be generally applicable to a wide range of grafting systems. 

Armstrong, and Rutherford have reported extensive studies on the vapor phase grafting of vinyl monomers to cellulosic fibers both mutual and pre-irradiation methods have been used (97, 120). Again, water or another swelling agent was found to be necessary for effective grafting to rayon and cotton for all the monomers studied. In the case of cellulose acetate water was helpful but not necessary except for styrene. Acetic acid and methanol vapors were also found to be effective promotors of vapor phase grafting to cotton and cellulose acetate fibers. 

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