Polymer 2 Flashcards
General properties of Polymers
-properties related to amorphous structere
-properties related to molcular bond
-properties related to mechanical behavure
properties related to amorphous structere
1- light in weight- low densitiy
2-translucent cuz its semi-cristline (if 100 amorphous then its transparent)
3-either less or more britile
4-have glasstransition temperature “ melting range”. [Tg] short
arrangment of atoms.
Proprties related to mouluclar bond 2ry between the polymar chain ( weak nd physical in nature)
1- low meting range of tm
2-high coofitent of thermal expantion
3-electricl and vhemical insulator
4-absorb h2o
5- low modules of elastic - flexible
6- low strenth - weak
7- low hardness - soft
- Mechanical behavior
1-The stress strain relationship of polymer compared to
ceramic & metal.
Metal
More flex
Weaker
More britle
Less ductile
More britle and less ductile
Ceramic
More flex
Weaker
Less britle
More ductile
- Mechanical behaviour
2- deformition
Initial strees on the polymer
Chain unfolding
Chain sliding
Further stress
Bond stretching
Bond breaking
- Mechanical behaviour
3-crazing
Voids in the polymer will open during suvice and form a fine cracks prepindicular on the force
Reasons for denture base crazing
1- due to mechanical stress during denture expantion
2-thermal stress mismatching
3-solvent action
Factors affecting the properties of
polymers:
1- structeral factors
2-additive factors
Structural factors
1-degree of polymraizition :
number of repting mers or units in the polymer chain
M.W. Of the polymer : m.w of mers x d.p
Chain legneth
The distribution of chain length is more important
than the molecular weight or degree of
polymerization. This explains the different strength
properties of two specimens of the same polymer
with the same M.W.
Chain lenght
Increasing the m.w and d.p will increase the chain length
Incres 2ry bond and enlargment will increase the strength
Structural factors: copolymrizition
Poly chain has more than one type of mers
1- random
2-graft
3-block
Effect:
-Graft and block improve the impact strenght proprteis
-talio maker
Structural factors: Crystallinity
The poly is usualy amophus with short chain , they are semi\crystalline with regions of crystals
surrounded by amorphous areas.
Crystal area = folded and extnded polymer chain
Amorphous = uncoordinated chain
Factors preventing high degree of
crystallization of polymers:
1- size of blundet groub
2- rapid cooling
3- high degree of polymrizition and molecular weight
4-network structer ( crosslinked)
Effect of crystallinity:
Increase:
-strenght
-density
-hardness
-tg
Decrease:
-water sorbtion transparency
I. Structural factors:
Glass transition temperature. [Tg]
Polymer state is soild
Above it = soft
Below it=hard
Structeral factors
Rate of loading:
Load and tm cause deformtion
Slow load and high tm results in more ducttile polymer
Rapid load and low tm results in britle polymer
Additives factors:
A- Effect of crosslinking:
Crosslinking premets the movment of polymers
Extnsive crosslinking results in more britle poly
Crosslinking increases
SHRB
Strenth
Hardness
Rigidity
Britlness
Tg
Crosslinking decreases
Dcft
Water sorbtion
Ductilty
Crazing
Flexibilty
Additives factors:
b. Plasticizers
External plast between the poly chain - intermoulcular bond-
To increase the intermolcular spacing
Interal the larger monomer size incrase their intamolcular spacing
Effect of plasticizer:
Increases
Flexibilty
Ductilty
Water sorbtion
Toghness
Decrease
Stifness
Strength
Hardness
Britlness
Tg
Additives factors:
c .Inorganic fillers:
Blending the polymer with Inorganic filler will increase the stifness only is
The filler is stronger than the poly and bonded to the poly matrix
Effect of addition of inorganic fillers
Incres the
Shrinkeg
Hardness
Stefness
Moduls of elastistiy
Decreses
Water sorption Heat
evolution Residual
monomer
Coefficient of thermal
expansion.
Polymerization
Additive factors:
d . Stabilizers:
• They are added to stabilize the properties of the
polymers.
