Yes, PLASTIC is a Scrabble word!

Letter values in Scrabble US: P 3, L 1, A 1, S 1, T 1, I 1, C 3.

Is it a valid word?

PLASTIC is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

generic name for certain synthetic or semisynthetic materials that can be molded or extruded into objects or films or filaments or used for making e.g. coatings and adhesives
a card (usually plastic) that assures a seller that the person using it has a satisfactory credit rating and that the issuer will see to it that the seller receives payment for the merchandise delivered

capable of being molded or modeled (especially of earth or clay or other soft material)
capable of being influenced or formed
forming or capable of forming or molding or fashioning

Also: credit card, charge card, charge plate.