Polymethyl methacrylate Flashcards Preview

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Flashcards in Polymethyl methacrylate Deck (12)
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1
Q

what are the ideal properties of PMMA

A

high thermal conduction - can feel temp of food
high YM and EL - rigid
low density - so it can be thin
good aesthetics
high softening temperature - doesnt distort

2
Q

what are the actual properties of PMMA

A

poor thermal conduction, low YM and EL - have to increase density to gain mechanical properties, softening temp is okay for food but not for cleaning - boiling water will distort, good aesthetics especially if used with acrylic teeth, dimensionally stable and accurate

3
Q

what is the reaction PMMA undergoes for production

A

free radical addition polymerisation

4
Q

what is the monomer used in the reaction

A

methacrylate monomer

5
Q

what is used in the production of PMMA

A

liquid - methacrylate monomer

powder - benzyl peroxide, PMMA particles, plasticer, pigments

6
Q

what are the stages required in production of PMMA

A

initiator, activation, polymerisation, termination

7
Q

what happens at the initiator stage

A

benzyl peroxide - this produces free radicals upon heat activation to result in free radical addition polymerisation

8
Q

what happens at the activation stage

A

heat activates the breaking of benzyl peroxide to release free radicals

9
Q

what happens at the polymerisation stage

A

free radicals break C=C in methacrylate monomer, this transfer the free radical to the monomer, as the monomer binds to other monomers, the free radical moves along to the next monomer, allows for polymerisation

10
Q

what happens if the material is over heated

A

cannot go above 100 degrees, if it does, results in gaseous porosity - affects strength and appearance, roughened surface can be sore on tough and plaque trap

11
Q

what happens if the material is cooled too quickly

A

results in internal stresses, over time, material cannot withstand stress and will eventually fracture

12
Q

why is it important to get the correct amount of monomer added

A

too much - polymerisation shrinkage

not enough - reduced mechanical strength