Grafting medium

Graft copolymerization of methylmethacrylate onto paper wood pulp using ceric ammonium nitrate as the initiator has been studied. Different experimental conditions have been used, including both water and water-organic solvent systems. The effects of composition of the grafting medium and grafting temperature on the grafting process are examined. 

By further increasing the methanol in the grafting medium, the graft yield decreases. This can be related to the lower solubility of the initiator in the grafting medium and a reduced formation of free radicals, which... 

The effect of the addition of acetone to the grafting medium has been investigated. The acetone-water system produces a high-grafting yield, especially at low concentrations of acetone in the grafting medium. This is explained by the inhibition of the formation of homopolymer. By increasing the ratio of acetone-water up to 8 22, the grafting yield is lower than that in case of the 8 22 methanol-water medium. 

Sodium bisulfite-china clay proved to be an efficient initiator for homopolymerization and graft polymerization of methyl methacrylate onto cellulose. Grafting reactions using ceric ammonium sulfate, sodium bisulfite-soda lime glass or -china clay are inhibited or retarded on adding soda lignin to the grafting medium. 

Crosslinkers are used in conjunction with the monomer to achieve certain desirable properties in the grafted membranes. The use of a crosslinker in the grafting medium has been investigated by different workers to obtain membranes that have improved stabiUty in fuel cells [72,115]. Lower graft levels are achieved as the crossHnker content in the grafting medium inaeases. This may be because the grafting starts at the film surface. In the presence of crossHnker, the very first polystyrene-grafted chains become crossUnked. 

Grafting parameters (irradiation dose, monomer concentration, grafting medium, temperature, etc.) have significant influence not only on grafting yield and grafting kinetics but also on resultant film and membrane properties. Crosslinkers are used in conjunction with the monomer to achieve certain desirable properties. For instance, the use of crosslinker is an effective means of enhancing the stability of styrene-grafted membranes in fuel cells. 

FIGURE 22.6 Schematics of various bioreactors for bone tissue engineering, (a) Perfusion bioreactor for cylindrical construct and its set up. The pump circulates media from medium reservoir, through the scaffold and back to the reservoir, (b) Perfusion bioreactor for anatomical TMJ graft. Medium is pumped into the TMJ scaffold from the bottom and exits on the side through needle outlet, (c) Combination of perfusion and compression bioreactor. Cells are exposed to both shear stress and pressure. 

---