Chapter 15 characteristics, application and processing of polymers Flashcards
mechanical properties of polymers
Stress-strain behavior
stress-strain curve for a material gives the relationship between stress and strain
mechanisms of deformation
brittle crosslinked and network polymers
mechanisms of deformation
semicrystalline (plastic) polymers
Predeformation by Drawing
Drawing…(ex: monofilament fishline)
Results of drawing:
Annealing after drawing
Predeformation by Drawing
Drawing…(ex: monofilament fishline)
- stretches the polymer prior to use
- aligns chains in the stretching direction
Results of drawing:
- increases the elastic modulus (E) in the stretching direction
- increases the tensile strength (TS) in the stretching direction
- decreases ductility (%EL)
Annealing after drawing
- decreases chain alignment
- reverses effects of drawing (reduces E and TS, enhances %EL)
Contrast to effects of cold working in metals!
mechanisms of deformation
elastomers
An elastomer is a polymer with viscoelasticity (i.e., both viscosity and elasticity) and with weak intermolecular forces, generally low Young’s modulus and high failure strain compared with other materials
thermoplastics
A thermoplastic is a type of plastic made up of polymer resins that becomes a soft material when it is heated and becomes hard when it is cooled.
thermosets
a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening (“curing”) a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure, or mixing with a catalyst.
Influence of Tand Strain Rate on Thermoplastics
decreasing
increasing
Time-Dependent Deformation
stress relaxation test
relaxation modulus
crazing
Crazing develops when excessive tensile stress is applied to a polymer, leading to microvoid formation in a plane normal to the stress.
two types of polymerization
addition - Polymerization that occurs through the coupling of monomers using their multiple bonds
condensation - The chemical mechanism that cells use to make and break polymers are basically the same in all cases. Monomers are connected by a reaction in which two molecules are covalently bonded to each other through loss of a water molecule;
polymerization
addition
polymerization
condensation
Polymer Additives ( 6 types )
Polymer Additives - improve mechanical properties (processability, durability etc)
Fillers
Plasticizers
Stabilizers
Lubricants
Colorants
flame Retardants
processing of plastics
Thermoplastic -
Thermoset -
Processing Plastics
Compression Molding
Compression molding is a method of molding in which the molding material, generally preheated, is first placed in an open, heated mold cavity.
Processing Plastics
Injection Molding
Injection moulding is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals, glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers.
Processing Plastics
Extrusion
type of polymer
fibers
fibers are a subset of man-made fibers, which are based on synthetic chemicals (often from petrochemical sources) rather than arising from natural materials by a purely physical process.
type of polymer
miscellaneous
Coatings
Adhesives
Films
Foams
Advanced Polymers
Ultrahigh Molecular Weight Polyethylene (UHMWPE) • Molecular weight
Outstanding properties
Important applications
Advanced Polymers
Thermoplastic Elastomers
Summary
Limitations of polymers
Thermoplastics
Elastomers
Thermosets
Polymer Processing
Polymer melting and glass transition temperatures •
Polymer applications
