Salient: Victoria University Students' Paper. Vol. 29, No. 6. 1966.

Urethane resins

Urethane resins

The urethanes find their main application where extreme conditions of moisture resistance, chemical resistance, and wear resistance are required. There are several types manufactured and commercially mailable in New Zealand.

(i) The one package oil modified type.

(ii) The one package moisture cured type.

(iii) The two package type.

(iv) Foam producing or plastic type.

The basic reaction of all four types involves the reaction between an isocyanate group (R — N = C = o) and hydrogen from a hydrogen donor. Modifications of the isocyanate compound and the hyorogen donor give the diflereut urethane types listed. All these products are manufactured in New Zealand based on overseas research.

(1) The one package oil modified urethane: This compound is formed by reacting toluene difsocvanatc with the hydroxyl group of an alkyd resin, e.g. a urethane modified alkyd is produced which cures by normal oil curing processes.

(ii) One package moisture cured urethane: Here toluene diisocyanate is reacted with a polylol such as polypropylene glycol to give an excess of free isocyanate groups. Polymerisation takes place With this isocyanate in contact with moisture-from the air or the substrate to which it is applied.

(iii) Two package type: This type is similar to the moisture cured type except the polylol component contains no free isocyanate and the hydrogen is provided by a polyether or a modified castor oil derivative.

(iv) Foam urethanes: The compounds used are similar to the two-can type but trichlorofluoromet hane is present to give gaseous bubbles. Somenines water Is present to produce the bubbles. Compounds such as silicones are present to control cell size and prevent cell rupture. By varying the molecular weight of the hvdroxvl containing compound so different flexibilities are achieved. The higher the molecular weight the greater the flexibility.

The flexible foams are used m pillows, cushions, etc, while the rigid foam is used in insulation of heal and sound and in articles such as surf boards.