Polymer Additives and Reinforcements

Polymer solubility-1

a) Polymer molecules in solid state just

after being added to a solvent

b) First step: a swollen gel in solvent

c) Second step: solvated polymer

molecules dispersed into solution

Schematic representation of the dissolution process for polymer molecules

Solubility depends on;

Crystalinity

Molecular weight

Branching

Polarity

Crosslinking degree

mmm STHG

Gibbs free energy

Enthalpy change during mixing

Entropy change during mixing

Solubility will occur if the free energy of mixing ∆Gm is negative.

The entropy of mixing is believed to be always negative.

Therefore, the sign and magnitude of ∆Hm determine the sign of ∆Gm.

Polymer solubility-2

Two-dimensional lattice model of solubility for a

low molecular weight solute

Polymer solubility-3

Two-dimensional lattice model of solubility for a

polymer solute

http://www.pslc.ws/macrog/ps4.htm

Water absorption of polymers

Polymer Water absorption(%)

polyester 0,2

polycarbonate 0,2

polystyrene 0,1

polyarcylonitrile 1,5

nylon 6,6 1,5

nylon 6 1,5

polytetrafluoroethylene 0

polypropylene 0

polyethylene 0

polyethyleneoxide 0,4

Polymer combustion

Polymer Combustion rate

(mm/min)

Sytrene-butadiene rubber 57

LDPE 39

HDPE 23

polypropylene 34

ABS 56

Inner portion that is not affected from

combustion

Heated layer

pyrolysis layer

gas layer

flammable Region

combustion products

Conductive Polymers

Electrical Properties-2

Polymer Dielectric constant

(1 kHz)

Dielectric Force

(kV/mm)

Natural rubber 2,9 50

ABS 2,9 18

Polycarbonate 4,4 33

Nylon 6,6 4,1 16

Polyethylene terephthalate 3,0 15

Poly (vinyl chloride) 3,4 22

Polyethylene 2,5 18

Density

Material Density

(g/cm3) Material

Density

(g/cm3)

Al 2,70 PVAc 1,19

Fe 7,87 PP 0,90-0,92

Cu 8,96 Nylon 11 1,04

Au 19,32 Nylon 12 1,02

LDPE 0,91-0,94 Nylon 6 1,12-1,13

PS 1,05 Nylon 6,6 1,13-1,15

PVC 1,37-1,39 PC 1,2

Natural rubber 0,91 PAN 1,17

PET 1,34-1,39 PFTE 2,27

Thermal and light stabilizers, antioxidants, and flame retardants. (influence essentially the chemical interaction of polymers with the environment)

Plasticizers, lubricants, impact modifiers, antistatic agents, pigments, and dyes. (usually employed to reduce costs, improve aesthetic qualities, or modify the processing,

mechanical, and physical behavior of a polymer)

These additives are normally used in relatively small quantities

Nonreinforcing fillers are employed in large quantities to reduce overall formulation costs

provided this does not result in significant or undesirable reduction in product quality or

performance

Alloying and blending

Polymer Additives and Reinforcements

Additives are usually required;

To impart stability against the degradative effects of

various kinds of aging processes

Enhance product quality and performance.

Plasticizers-I

The principal function of a plasticizer is to reduce the Tg of a polymer so

as to enhance its flexibility over expected temperatures of application.

Plasticizers are usually high boiling organic liquids or low melting solids. They are also sometimes moderate-molecular-weight polymers. Like ordinary solvents, plasticizers act through a varying degree of solvating action on the polymer. Plasticization is difficult to achieve in nonpolar polymers like polyolefins and highly crystalline polymers.

Polymer plasticization can be achieved either through internal or external incorporation of

the plasticizer into the polymer.

a) Internal plasticization involves copolymerization of the monomers of the desired polymer

and that of the plasticizer so that the plasticizer is an integral part of the polymer chain. Tg. The

most widely used internal plasticizer monomers are vinyl acetate and vinylidene chloride.

b) External plasticizers are those incorporated into the resin as an external additive. Typical

low-molecular-weight external plasticizers for PVC are esters formed from the reaction of acids

or acid anhydrides with alcohols.

Plasticizers-II

Monomeric plasticizers ( phthalate, terephthalate, adipate, phosphate esters)

Polymeric and permanent plasticizers (Linear polyesters obtained from the reaction of dibasic acids such as adipic, sebacic, and

azelaic acids with a polyol )

Polymeric stabilizers have higher molecular weights than the monomeric

plasticizers, and less volatile when exposed to high temperatures either during processing or in

the end-use situations, less susceptible to migration and less extractible.

Epoxy Plasticizers (derived from vegetable oil, epoxidized soybean is an example)

confer heat stability and light stability on PVC products

have relatively low-temperature properties

The ideal plasticizer must satisfy three requirements;

Compatibility

Permanence requires low volatility, extractability, nonmigration, and heat

and light stability. Lack of permanence involves long-term diffusion into the

environment.

Efficiency

Also it should be odorless, tasteless, nontoxic, nonflammable and heat stable

Fillers and Reinforcements (Composites)-1

Different types of fillers are employed in resin formulations.

-Added to improve tensile strength & abrasion resistance,

toughness & decrease cost

The most common are;

calcium carbonate,talc, silica, wollastonite, clay, calcium sulfate,

mica, glass structures, and alumina trihydrate.

Particulate-filled composites are generally isotropic (they are invariant with direction provided there is a good dispersion of the fillers)

Fiber-filled composites are typically anisotropic. Fibers are usually

oriented either uniaxially or randomly in a plane. In this case, the

composite has maximum modulus and strength values in the

direction of fiber orientation.

For uniaxially oriented fibers, Young’s modulus, measured in the orientation direction

(longitudinal Modulus, EL)

Where Ef is the tensile modulus of the fiber, Em is the modulus of the matrix resin and

is the volume fraction of the filler. f

Fillers and Reinforcements (Composites)-2

Alloys and Blends-I

An alternative to the development of new polymers is the development

of alloys and blends that are a physical combination of two or more

polymers to form a new material.

To combine the best properties of each component in a single

functional material that consequently has properties beyond those

available with the individual resin components and that is tailored to

meet specific requirements.

To optimize cost/performance index and improve processability

of a high-temperature or heat-sensitive polymer.

The composition dependence of a given property, P, of a two-component polymer system may be

described by;

where P1 and P2 are the values of the property for the isolated components and C1, C2 are,

respectively, the concentrations of the components of the system. I is the interaction parameter that

measures the magnitude of synergism resulting from combining the two components

Alloys and Blends-II

Alloys and Blends-III

Examples of the most significant commercial

engineering alloys are polystyrene (PS)-modified

poly(phenylene oxide) (PPO) and polystyrene (PS)-

modified poly(phenylene ether) (PPE).

We can combine amorphous polymer with a crystalline polymers to exploit the strengths of

each component while deemphasizing their weakness.

Example: Nylon, PET, PBT- crystalline polymers and offer excellent resistance, processing

ease and stiffness

PC and polysulfone (amorphous polymers) outstanding impact strength and dimensional

stability.

PC/PET blends (replacement for metal, including automotive, lawn and garden appliances

and electrical/electronic,consumer, industrial/mechanical, sporting and recreation, and

military equipment.)

Nylon/PPO blends (fenders and rocker panels of some automobiles, applications

demanding chemical resistant performance under high impact and high heat.

Antioxidants and Thermal Stabilizers

Antioxidants

Free radical scavengers (Primary antioxidants, radical or chain terminators)-inhibit

oxidation through reaction with chain-propagating radicals

Ex: hindered phenols and aromatic amines

Peroxide decomposers (secondary antioxidants or synergists)- break down

peroxides into nonradical and stable products.

Ex:Organic phosphites and thioesters that serve to suppress homolytic breakdown.

Thermal Stabilizers; Thermal stabilizers may be based on one or a combination of the following classes of

compounds;

Barium/cadmium (Ba-Cd), calcium/zinc (Ca-Zn), organotin, organo-antimony,

phosphite chelates, and epoxy plasticizers.

Ba/Cd stabilizer systems, which represent the largest share of the PVC stabilizer

market, are available as liquids or powders.

UV stabilizers

UV radiation in the range 290 to 400 nm has potentially degradative effects on polymers since most polymers contain chemical groups that absorb this radiation and undergo chain scission, forming free radicals that initiate the degradative reactions.

UV stabilizers are employed to impede or eliminate the process of degradation and, as

such, ensure the long-term stability of polymers, particularly during outdoor exposure.

Light stabilizers are typically UV absorbers or quenchers.

The former preferentially absorbs UV radiation more readily than the polymer, converting the energy into a harmless form.

Quenchers exchange energy with the excited polymer molecules by means of an energy

transfer mechanism.

Other UV stabilizers deactivate the harmful free radicals and hydroperoxides as soon as they are formed

Flame Retardants

The function of flame retardants in a resin formulation is ideally the

outright inhibition of ignition where possible. Where this is impossible,

a flame retardant should slow down ignition significantly and/or inhibit

flame propagation as well as reduce smoke evolution and its

effects.

The presence of flame retardants also tends to cause substantial

changes in the processing and ultimate behavior of commercial resins.

The burning characteristics of polymers are modified by

certain compounds;

aluminatrihydrates;

bromine compounds;

chlorinated paraffins and cycloaliphatics;

phosphorus compounds,notably phosphate esters;

and antimony oxides, which are used basically as

synergists with bromine and chlorine compounds

Flame retardants can be classified as; (based on

the method of incorporation in the resin

formulation or mode of action)

Additives

Reactives

Intumescents

Nonflame retardant systems

Colorants-I

The marketability of a polymer product quite frequently depends on

its color; therefore the purpose of adding a colorant to a resin is to

overcome or mask its undesirable color characteristics and enhance

its aesthetic value without seriously compromising its properties and

performance.

Colorants are available as; (they can be natural or synthetic)

Organic pigments -generally transparent, good brightness,

variable heat stability, light and migration fastness

Dyes-stronger, brighter and more transparent than pigments

- have poor migration fastness

Inorganic Pigments –largely mixed with metal oxides, generally

good to excellent light and migration fastness but variable

chemical resistance

Colorants are used in polymers either as raw pigments (and dyes), concentrates or precolored

compounds.

Colorants are avalaible in a variety or forms, including pellets, cubes, granules, powder, liquid, and

paste dispersions

Colorants-II

Selecting a colorant for particular application;

The ability of the colorant to provide the desired color effect

Withstand not only process temperature (heat stability) encountered

during manufacture but also, for possible prolonged times, the

temperature in the end-use requirements

Migration fastness is related to the solubility of the colorant in the polymer.

Color migration is manifested by bleeding, blooming or plate-out

Inadequate light fastness of a colorant is manifested in the form of fading or

darkening

The colorant must be compatible with the base resin forming a homogeneous

mass and also it must not degrade or be degraded by the resin

Incompatibility of the colorant can affect mechanical properties, flame

retardancy, weatherability, chemical and UV resistance, heat stability of the resin

through interaction of the colorant with the resin and its additives.

Antistatic agents

Antistatic agents are hydroscopic chemicals that can generate layer of water

for the removal of static charges generated on the polymer by pulling moisture

from the atmosphere.

There are essentially two types of antistats that are commonly used in

polymers to get rid of static electricity: those that are applied topically and

those that are incorporated internally into the polymer.

Both improve the conductance of polymer surfaces by absorbing and holding a

thin, invisible layer of moisture from the surrounding air onto the polymer

surface.

Major types of organic antistatic agents include quaternary ammonium

compounds, amines and their derivatives, phosphate esters, fatty acid

polyglycol esters, and polyhydric alcohol derivatives such as glycerine and

sorbitol.

Selection of the appropriate antistat depends on its compatibility with the

polymer, the end use of the part, and the desired level of antistatic activity.

Other factors that need to be considered include the effect of antistatic agent

on color, transparency, and finish of the polymer part; its possible toxicity;

stability during processing; and degree of interference with physical properties

and ultimately cost effectiveness.