Plastics and Composites Welding of Plastics Polymers Polymer

Plastics and Composites

Welding of Plastics Polymers • Polymer - a single building block (mer) is repeated to form a long chain molecule – Thermoplastic polymers soften when heated, harden when cooled • 2 -liter bottles – Thermosetting polymers don’t soften when heated • Car tires, caulking compound (Poly)ethylene H H C=C H H add H 2 O 2 HH ··· -C-C- ··· HH

Curing of Polymers Types of Thermoset Polymers • Anaerobic Cyanoacrylates • Epoxies Urethanes • Silicones • Thermosets form long polymer chains by chemical reaction (curing) – Heat is the most common means of curing – Ultraviolet light, oxygen - acrylics – Moisture – Cyanoacrylates (superglue) 0. 1. 1. 2. 6. T 26. 95. 12

Moffatt, Pearsall, & Wulff, “The Structure and Properties of Materials”, John Wiley & Sons.

Curing of Polymers • Thermoplastics (hotmelts) – Adhesive is heated until it softens, then hardens on cooling -Polyethylene, PVC 0. 1. 1. 2. 6. T 26. 95. 12

Materials, Scientific American Book, W. H. Freeman & Company

1 B 3 D C A 2 Materials, Scientific American Book, W. H. Freeman & Company

Cautions • Some older tests for plastic recognition suggested burning of the polymer and noting its flame and smell. Some materials can emit harmful vapors so this is not recommended for a class exercise, and should be done only under controlled conditions. • Any heat applied to a plastic should be done in a ventilating hood.

Composite Materials Wood Cross Section Materials, Scientific American Book, W. H. Freeman & Company

Composite Fiber Properties Stiffness Strength Materials, Scientific American Book, W. H. Freeman & Company