hrvatski

Smjerovi razvoja proizvodnje pjenećeg polistirena

A number of processes have been developed to prepare polystyrene foams (PS-E) and the two most important are, respectively: extrusion for the production of foamed sheet or foamed board, and the preparation of expandable beads. In the former process, the blowing agent is mixed into the molten polymer in an extruder under pressure. The blowing agent vaporises as the pressure in the polymer melt decreases at the die-exit, causing the polymer to expand. However, the most applied process is by incorporation of the blowing agent in expandable PS beads which can be achieved by the addition of the blowing agent, mostly pentane isomers, after the suspension polymerisation process. Recently, advanced processes include addition of the blowing agent during the suspension process therefore an narrow particle size distribution is of primary importance. Moreover, it was shown that using bifunctional peroxy initiators in styrene polymerisation, the high monomer conversion and narrow molecular mass distribution could be achieved. Conventional PS-E typically contains 7-8 wt.% of pentane isomers (mainly n-pentane and iso-pentane) as the physical blowing agent. This blowing agent is capable of expanding the compact PS beads upon heating the material above its glass transition temperature (Tg). Undesirable emissions of the hydrocarbons as blowing agent and its high flammability are the complications of this process. Therefore new processes for the production of expandable polystyrene have been developed, particularly using water as the blowing agent. Water is trapped inside the polystyrene matrix through the use of modified starch, PS-Clay nanocomposite or mostly by introduction an hydrophilic (ionic) part via copolymerization reaction as sodium styrenesulphonate, vinyl pyrolidone, (met)acrylic acid, maleic anhydride, vinyl acetate etc. that is introduced as a separate phase during the suspension polymerization. Brominated cyclic compounds are still the major flame retardants for polystyrene foam such as hexabromocyclododecane, tetrabromoethylcyclohexane and brominated cyclic allyl ethers, and by addition of small amounts of organic peroxides the synergistic effect is obtained. When they contain bromine atoms in the ortho-position to an allyloxy group, brominated phenyl allyl ethers belong to the same class of additives. An overview of advanced processes for expandable polystyrene production particularly in styrene suspension polymerization as well as production of a flame retarded foam are presented.

pjeneći polistiren; suspenzijska polimerizacija; pjenila; pjenjenje s vodom; pjeneći polistiren smanjene gorivosti

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