lecture_9_-_polymers_-_chapter_8 - ME 350 Lecture 9 Ch 8...

ME 350 – Lecture 9 – Ch 8
Natural Rubber
Nylon (replaces silk)
PVC
Kevlar (replaces metal alloys)
HDPE
(replaces cast iron, Cu)

Polymers
•
Polymers are described as plastics and
rubbers
•
Three categories:
1. Thermoplastic polymers
2. Thermosetting polymers
3. Elastomers
•
Which are plastics? # 1 & 2
•
Which are rubbers? # 3

Thermoplastic Polymers - Thermoplastics
Solid materials at room temperature but viscous
liquids when heated
•
Can be easily and economically shaped into
products
•
Can be subjected to heating and cooling cycles
without significant degradation: repeatedly
•
Symbolized by TP

Thermosetting Polymers - Thermosets
•
Cannot tolerate repeated heating cycles
–
When initially heated, they soften and flow for
molding
–
Elevated temperatures produce: a chemical
reaction that hardens the material into an
infusible solid
–
If reheated, rather than soften, thermosets:
degrade and char
•
Symbolized by TS

Elastomers (Rubbers)
Polymers that exhibit extreme elastic
extensibility
•
Some elastomers can be stretched by a factor
of 10 and yet completely recover to their
original shape. What would its EL% be? 900%
•
Although their properties are quite different
from thermosets, they share with thermosets a
similar: molecular structure

Polymer Notation
MW of one
monomer?
C (12) = 24
H (1) = 3
Cl (36) = 36
MW = 63

Polymerization
•
Addition polymerization
–
Model of addition (chain) polymerization: (1)
initiation, (2) rapid addition of monomers, and (3)
resulting long chain polymer molecule with n mers
at termination of reaction