1. Chemical and Physical Properties Chapter 5
Professor Joe Greene
CSU, CHICO
MFGT 041

2. Chapter 5 Objectives Objectives
Thermal Properties (energy inputs, thermal stability temperature, glass transition and melting temp)
Weathering (UV degradation and oxidation)
Chemical resistivity and solubility
Permeability
Electrical Properties
Optical Properties
Flamability

3. Thermal Properties
Plastics properties are affected by mechanical forces (Chap 4) as well as environmental exposure to heat, UV, moisture, salt sprays, solvents.
Energy Inputs
Thermal or UV can cause
Degradation or burning which breaks the covalent bonds
Softening or thermal transitions break hydrogen bonds and untangle polymer chains
Key thermal transitions are
Melting temperature: polymer becomes amorphous
Glass Transition temperature: glassy state to rubbery state

4. Form of Polymers
Thermoplastic Material: A material that is solid, that possesses significant elasticity at room temperature and turns into a viscous liquid-like material at some higher temperature. The process is reversible
Polymer Form as a function of temperature
Glassy: Solid-like form, rigid, and hard
Rubbery: Soft solid form, flexible, and elastic
Melt: Liquid-like form, fluid, elastic
Temp
Glassy
Rubbery
Melt
Polymer
Form
Increasing Temp Tm Tg

5. Glass Transition Temperature, Tg
Glass Transition Temperature, Tg: The temperature by which:
Below the temperature the material is in an immobile (rigid) configuration
Above the temperature the material is in a mobile (flexible) configuration
Transition is called “Glass Transition” because the properties below it are similar to ordinary glass.
Transition range is not one temperature but a range over a relatively narrow range (10 degrees). Tg is not precisely measured, but is a very important characteristic.
Tg applies to all polymers (amorphous, crystalline, rubbers, thermosets, fibers, etc.)

6. Glass Transition Temperature, Tg
Glass Transition Temperature, Tg: Defined as
the temperature wherein a significant the loss of modulus (or stiffness) occurs
the temperature at which significant loss of volume occurs
Modulus
(Pa) or
(psi)
Temperature
-50C
50C
100C
150C
200C
250C Tg
Vol.
Temperature
-50C
50C
100C
150C
200C
250C
Amorphous
Crystalline Tg

7. Thermal Stability Temperature
Maximum use temperature
Rule of thumb: Plastic material should not be used at temperatures above 75% of Tg.
Example: Tg of ABS is 100°C. Then the maximum use application for the ABS pipe should be 75°C
Figure 5.1
Amorphous Materials
Melt, rubbery, stiff
Have a reported Tg
Crystalline materials
Melt, stiff
Have a reported Tm, Tg is
not usually used
Themoset Materials
Have a Tg where they lose modulus
Leathery
Vol.
-50C
50C
100C
150C
200C
250C
Amorphous
Crystalline Tm Tg
Hard,
Stiff
Melt
Tchar
Char
Temperature

8. Crystalline Polymers Tg
Tg: Affected by Crystallinity level
High Crystallinity Level = high Tg
Low Crystallinity Level = low Tg
Modulus
(Pa) or
(psi)
High Crystallinity
Medium Crystallinity
Low Crystallinity Tg
Temperature
-50C
50C
100C
150C
200C
250C

9. Thermal Properties
Table 3.2 Thermal Properties of Selected Plastics

10. Additives
Environmental effects can be mitigated with the use of additives
Antioxidants: Oxidation of plastics involves oxygen in a series of chemical reaction that break the bonds of the polymer and reducing the molecular weight down into a powder.
Primary antioxidants work to stop or terminate oxidation reactions
Secondary antioxidants work to netralize reactive materials that cause oxidation
Susceptible Materials: PP and PE oxidize readily
Major types
Phenolic
Amine
Phosphite
Thioesters

11. Additives Antistatic Agents Flame Retardants
Compounded into plastic attract water to surface and thus making it more conductive to dissipate charges
Major types
amines, quarternary ammonium compounds, phosphates, glycol esters
Flame Retardants
Emit a fire-extinguishing gas (halogen) or water when heated,
Swell or foam the plastic and forming an insulating barrier against heat and flame
Based on combinations of bromine, chlorine, antimony, boron, and phosphorous
Major Types
alumina trihydrate (ATH emits water), hologenated materials (emit inert gas), phosphorous compounds form char barriers

12. Additives Heat Stabilizers Impact Modifiers
Retard thermal decomposition for PVC
Based on lead and cadmium in past. 28% Ca pollution came from plastics
New developments based on barium-zinc, Ca-zinc, Mg-Zinc, etc..
Impact Modifiers
Elastomers added to polymers
PVC is toughened with ABS, CPE, EVA, etc.

13. Additives Lubricants Needed for making plastics.
Reduce friction between resin and equipment
Emulsify other ingredients with lubricant
Mold release for the mold
Causes surface blemishes and poor bonding
Common materials
waxes (montan, carnauba, paraffin, and stearic acid)
metallic soaps (stearates of lead, cadmium, barium, calcium, zinc) Table 7-1

14. Additives Plasticizers
Chemical agent added to increase flexibility, reduce melt temperature, and lower viscosity
Neutralize Van der Waals’ forces
Results in leaching for
Food contamination
Reduced impact and reduced flexibility, PVC hoses
Over 500 different plasticizers available
Examples: Dioctyl phtalate (DOP), di-2-ethylhexyl phthalate (carcinogenic in animals)

15. Additives Preservatives Processing Aids
Protects plastic (PVC and elastomers) against attacks by insects, rodents, and microorganisms
Examples
Antimicrobials, mildewicides, fungicides, and rodenticides
Processing Aids
Antiblocking agents (waxes) prevents sticking
Emulsifiers lowers surface tension.
Detergents and wetting agents (viscosity)
Solvents for molding, painting, or cleaning

16. Additives UV Stabilizers Plastics susceptible to UV degredation are
Polyolefins, polystyrene, PVC, ABS, polyesters, and polyurethanes,
Polymer absorbs light energy and causes crazing, cracking, chalking, color changes, or loss of mechanical properties
UV stabilizers can be
Carbon black, 2-hydroxy-benzophenones, 2-hydroxy-phenyl-benzotrizoles
Most developments involve hindered amine light stabilizers (HALS)
HALS often contain reactive groups, which chemically bond onto the backbone of polymer molecules. This reduces migration and volatility.

17. Additives Heat stabilizers
Retard decomposition of polymer caused by heat , light energy, or oxidation, or mechanical shear.
PVC has poor thermal properties and has used a large amount of stabilizers, mostly cadmium based. (28% of waste Cd from PVC)
Lead and cadmium stabilizers have been replaced with
barium-zinc, calcium-zinc, magnesium-zinc, phosphite formulations

18. Testing Electrical Testing Conditioning samples Dielectric Strength
Plastics are good insulators, handles for screw divers etc.
Ability to withstand exposure to electrical current.
Conditioning samples
ASTM D-618: 73F (23C) and RH of 50% for > 40 hours
Dry samples to get consistent results
Dielectric Strength
Amount of voltage required to arc through a specimen of plastic (figure 10-1)
Voltage starting at 0 Volts is applied to one side of specimen and increased until it arcs through.

19. Testing Dielectric Constant Volume Resistivity Surface Resistivity
The electrical capacitance of a specific plastic cross section as a ratio to that of a similar cross section of air.
Volume Resistivity
Ability of a plastic to resist an electric current through its bulk. (Fig 10-3) Used for electrical insulators.
Surface Resistivity
Ability of a plastic to resist current across its surface. (Fig 10-5)
Arc Resistance
Amount of time required for an electrical arc to carbonize the surface of a specimen. (Fig 10-5)

20. Testing Permeability How easily gases or liquids pass through material
Diffusion Constant, D
Characteristics of material (plastic, metal, or ceramic)
If plastic material is solvent sensitive to a particular gas or liquid then D is large.
High D equals high permeability or low barrier properties
Diffusion variables, Figure 5.5

21. Testing
Permeability
Barrier Properties of Plastic Materials, Table 5.2
Packaging materials need to keep foods fresh and away from moisture, oxygen, or keep CO2 in soda or beer.
Barrier properties are due to chemical structure
Polar films let polar gases through but not nonpolar
Non-polar films let non-polar molecules but polar
Example,
ethylene vinyl alcohol (polar due to polar groups along chain) has low permeation rate for O2 (non-polar) but a high permeation rate for water (polar)
Polyethylene is has no polar groups along chain and has low permeation for water but a much higher rate for non-polar oxygen
Barrier properties can be modified with additives, or with multilayer films.