Lecture 9 Flashcards
structural components of composites?
Matrix (blend of aromatic and / or aliphatic dimethacrylate monomers)
The main component
Fillers (eg. glass particles - added for reinforcement, reducing shrinkage, dimensional stability, …etc)
Experimental values
Must experiment to see how much to add for best results
Coupling agent (eg. organosilanes to promote adhesion between matrix and fillers)
Activator-initiator system (free radicals activated by light)
Use the blue lightenergy source
- Pigments
Inhibitors (added to minimize spontaneous or accidental polymerization of monomers
This helps prevent blue light in other stations from curing the composite in your station
Basically, gives a minimum about of blue light needed to polymerizeonly can come from the blue light in your curing light right next to the tooth
Optical Modifiers (added for shading and translucency) – eg. Pigments
Not needed in amalgams
Strontium and yttrium
Add very small amounts
advantages of biopolymers?
Easy to fabricate into oils, films, fabric, yarn, solids
Non-corrosive
Bear close resemblance to tissue
Density of biopolymer is close to tissue density
Good adhesion properties
Used for hernias
disadv of biopols?
Poor load bearing properties, viscoelastic and viscoplastic flow
Usually can’t get totally polymerized, thus biodegradation by leaching is a major problem
Non-conversion is a biocompatibility problem
Most commercial polymers have additives that can not be used in the body
Serves no purpose in the body
give examples of biopolymers
UHMWPE
Ultra-high molecular weight polyethylene
Used for TMJ prostheticcup for the metal condoyle (?)
to move in
Switched from teflon to UHMWPE because teflon wore
away quickly
Can give out if used for surgery
If the material is not smooth, it can lead to catching or
locking
This is for UHMWPE
PMMA
Poly methyl methacrylate
Very exothermicgoes to 140 C can burn
In crazy glue
Nylon
Polypropylene
Silicone
compare and contrast step pol vs chain pol
chain: monomer conc decreases steadily, but high MW molecule formed early on, so MW stays steady?
step: one-by-one monomer added, long time = high MW
what is tacticity in polymers?
–>deals with the arrangement of the side chain (R) in the chain;
atactic = R on either side of the chain (random)-->arranged randomly in the molecule syndiotactic = alternating R's; ordered? isotactic = all Rs on the same side of the chain
what is vulcanization?
the addition of sulfur to cis-polyisoprene to change the rubber from a cold-brittle hot-sticky rubber to a rubber with the desired elasticity and hardness
what is cis/trans geometric isomerism?
the form of configuration describing the orientation of funtional groups
if an isomer contains double bonds, the groups cannot rotate; similarly, if the pendant is too big or there is a ring with too much stearic hindrance, it cannot rotate easily either
study slide 23
ye
what are the polymer solubility rules?
Polar molecules dissolve polymers with polar groups
Non-polar molecules dissolve non-polar groups
Straight chain solvents dissolve straight chain polymers
Aromatic solvents dissolve aromatic polymers
Crystallinity protects against solubility
Water does not dissolve polymers, but may cause swelling
Diffuse into the layers and cause expansion
Organic solvents dissolve polymers. Most resistant are: Teflon, PE, and vinyl)
what are the bonds, most to least stable?
C – C C – O C – S C – N C = C Si - O
. Bonds can be protected by adding specific groups to sites adjacent to the bond
3. Protect against solvation by using: high MW, high crosslinkage, and high crystallinity
prevent from being dissolved
- Bonds can be protected by adding specific groups to sites adjacent to the bond
- Protect against solvation by using: high MW, high crosslinkage, and high crystallinity
prevent from being dissolved
ye
what are the possible ways a biopolymer may degrade in a biological environment?
By microorganism attack – polymer eating bacteria?
Enzyme attack - catgut sutures degrade by enzyme attack
Free radical attack – by free radicals present in cells?
polymers solubility in the body
Some absorption always occurs (substances enter the polymer). Famous case in 1968 of heart valve failure and death. Involved silicone taking up lipids, swelled, and got stuck.
Some leaching often takes place (low MW additions, impurities, or unreacted mer leak out)
