John L. Garnett

Grafting of methyl methacrylate to cellulose and polypropylene with UV and ionising radiation in the presence of additives including CT complexes

Detailed studies of the grafting of polar methyl methacrylate (MMA) to two representative backbone polymers, cellulose and polypropylene (PPE) in the presence of additives, using ionising radiation and UV as initiating sources, are reported. The results are compared with analogous grafting work with non polar styrene previously studied. The additives chosen for examination were predominantly components used in radiation curing formulations since grafting and curing are known to be mechanistically related. The additives were mineral acid, photoinitiators, vinyl ethers, oligomers, polyfunctional monomers including multifunctional acrylates (MFAs) and methacrylates (MFMAs). For the first time charge transfer (CT) monomer complexes have been used as additives in the current work. The CT complexes themselves, being monomers, have also been directly radiation grafted to cellulose. Mechanisms for the above grafting processes are proposed. The significance of this grafting work in analogous radiation curing is discussed. The grafting of the CT complexes, themselves, is shown to lead to new copolymers with potential industrial applications.

Significance of grafting in curing processes initiated by UV, excimer and ionising radiation sources

Abstract The grafting of a typical methacrylate monomer (MMA) to polypropylene (PPE) and cellulose initiated by UV and ionising radiation is reported. The effect of additives which constitute components in radiation curing on the grafting process is examined. Additives studied include photoinitiators (PIs), multifunctional acrylates and methacrylates and acrylate oligomers. Synergistic effects when these additives are combined in the same solution are reported. The photografting studies have been extended to include grafting with charge transfer (CT) complexes involving donor/acceptor (DA) monomers to PPE, cellulose and wool. The importance of this work in conventional and PI free curing is discussed, particularly the significance of concurrent grafting during curing.

Cure grafting - a complementary technique to preirradiation and simultaneous processes?

Abstract A novel radiation grafting process, termed cure grafting, based on curing of donor/acceptor (DA) monomers as charge transfer complexes initiated by UV or any ionising radiation source, is proposed. The system is complementary to the existing preirradiation and simultaneous radiation grafting methods. The advantages and disadvantages of cure grafting are summarised. Examples of cure grafting using representative DA monomers are described with cellulose as model substrate in the presence of UV or EB. A unique property of cure grafting is that the yield is known quantitatively prior to irradiation.

Role of additives in wood–polymer composites. Relationship to analogous radiation grafting and curing processes

Abstract Wood polymer composites (WPC) were prepared by impregnating an Australian softwood, Pinus radiata with methyl methacrylate which subsequently underwent in situ polymerisation utilising either γ radiation or the catalyst–accelerator method. Novel additives including thermal initiator, crosslinking agents, an inclusion compound and oxygen scavenger were incorporated to improve the polymer loading and properties of the resulting WPC. Polymer loadings of WPC obtained utilising the accelerator–catalyst method corresponded well with those obtained using γ radiation with 20 kGy radiation dose. The mechanistic significance of the current work in analogous radiation grafting and curing processes is discussed.

Effect of monomer structure on radiation grafting of charge transfer complexes to synthetic and naturally occurring polymers

Abstract Effect of monomer structure in photografting charge transfer (CT) complexes to typical substrates like wool, cellulose and polypropylene is reported. The importance of photoinitiators in these processes is examined. Maleic anhydride (MA) with triethylene glycol divinyl ether (DVE-3) is used as reference CT complex in this work. The additional monomers studied include the esters of MA as acceptors and vinyl acetate as donor. The role of solvent in these reactions is discussed, particularly the effect of aromatics in photografting to naturally occurring trunk polymers like wool and cellulose. The effect of the double bond molar ratio of the DA components in grafting is examined. The ultraviolet (UV) conditions for gel formation during photografting, hence the importance of homopolymer yields in these processes is reported. A plausible mechanism to explain the results from this photografting work is proposed. The significance of these photografting studies in the related field of curing, especially in UV and ionising radiation systems, is discussed.

Novel additives including charge-transfer complexes in grafting of methyl methacrylate to polypropylene, cellulose and wool, initiated by ionizing radiation and UV: significance of these studies in analogous curing processes

Photoinitiators recently developed for UV curing of pigmented finishes have been used to accelerate the grafting of a typical acrylate monomer, methyl methacrylate (MMA), to a variety of backbone polymers, cellulose, wool and polypropylene (PPE). Both UV and γ-radiation sources have been used to initiate reaction. Novel charge-transfer (CT) monomer complexes involving electron rich donors (D) and electron poor acceptors (A) have also been used as additives in these reactions. The DA complexes themselves have been directly grafted to cellulose to produce unique copolymers. Mechanisms for the above grafting processes are proposed. The significance of this grafting work in analogous radiation curing is discussed.

Significance of radiation grafting in curing processes: Role of additives in these reactions

Abstract The importance of observing concurrent grafting with curing in polymerisation processes initiated by UV and ionising radiation is discussed. Methyl methacrylate (MMA) is used as monomer with cellulose and polypropylene (PPE) as backbone polymers in the model grafting system studied. The styrene comonomer technique is utilised to overcome homopolymerisation in these reactions. The effect of typical materials used in curing processes as additives in grafting has been examined. The additives used include mineral acids, photoinitiators, thermal initiators, a typical inclusion compound like urea and polyfunctional monomers especially the multifunctional acrylates and methacrylates. A representative commercial curing process where these grafting concepts are relevant is discussed in detail. The process chosen for illustration is the UV cured banknote, a world first. A theory to explain the observed reactivity in grafting and curing is proposed involving physical and chemical processes which act in concert. The physical process involves partitioning of reagents whereas the chemical process concerns additional radical reactions in the radiation initiation step.

CT complexes in radiation polymerisation processes including grafting, curing and hydrogel formation

Abstract Parameters influencing the grafting of a typical charge transfer (CT) complex, maleic anhydride /triethylene glycol divinyl ether, to representative substrates, cellulose and polypropylene, initiated by UV and ionising radiation have been investigated. The variables studied include effect of solvent, role of donor involving the type of ether and the nature of the acceptor including the use of common monomers like methyl methacrylate. A novel application of this CT grafting work is reported involving hydrogel formation with subsequent controlled release of incorporated reagent.