Week 14 Vinyl acetate resins Flashcards
History of Polyvinyl Acetate
originally used as resin systems, used commercially in the 1920s. beads which dissolve in an organic solvent
also as an emulsion/ aqueous dispersion.
History of Polyvinyl acetate (PVA) use in Conservation
polyvinyl acetate- what is the structure, how is it formed as a polymer
properties of polyvinyl acetate as a homopolymer, adhesive and consolidant
typical co-polymers of vinyl acetate
more internal volume, more flexibility.
homopolymers have a higher film forming temperature compared to co-polymers
what are plasticisers, some examples, how does it change the properties
vinyl acetates in the form of dispersions vs in a solvent
yellowing because of additives, to make it compatible with the water
disadvantages of dispersion systems (PVAs)
how does PVAc decay
hydrogen is just left, acetic acid is produced
potential modification of PVAc Dispersions
How PVAc is modified at the production stage
What is poly(vinyl alcohol)/ PVAL. How is it produced
Polyvinyl alcohol properties
used on postage stamps
How is the stability of PVAL
not very stable, reacts with light and heat to cross link
hygroscopic because of the side group
diagram shows cross linking process
uses of polyvinyl alcohol
partial substitution makes it compatible with water
polyvinyl acetals: how are they produced. resulting properties
properties of polyvinyl acetals
uses of polyvinyl acetals
uses of polyesters
As textiles and supports for conserving textiles
polyester: basic structure
forms by condensation reaction
means susceptible to hydrolysis break down in the future
polyester: molecular form and properties
examples of different polyester plastics used in plastic bottles
polyester casting resins: structure and cross linking process
disadvantages of polyesters
short shelf life of catalyst
polyester: uses in conservation
yellows quickly as a gap filler
Polyurethane Foams and varnishes: composition and properties
Silicones and silanes: what are they made of. How would you modify the structure of silicic acid to alter the properties
Often mould making and sealants
consolidants and coatings (conservation)
adding carbon and hydrogen to the structure alters properties.
OH groups can react with materials like stone, modification gives it (an inorganic compound) organic properties
Different names for this molecule
Silicon can have both O______ and I_______ linkages
how to create silicone systems which are substituted with organic groups
with a catalyst and a condensation reaction
once the OH groups are hydrolysed with a catalyst they can react with moisture in the atmosphere and form bonding with surfaces
What would be the property of a polymer with Si-O chains with organic side groups
the oxygen in the chain has polarity (moisture attracting), while there is also a hydrophobic structure with the organic side groups
How do you polymerise silicon based molecules and form siloxanes. also what are the advantages of this system for consolidates
put a monomer into a porous structure, it polymerises and forms a structural network. easier than capillaries trying to put in a large molecule.
use of silanes are coupling agents in adhesion
glass is hard to join together because of its surface energy. you can have an adhesive side chain added to silicon (eg an acrylic resin). the OH groups on the silicon group can react with the OH on the glass. this is a good primer to attach more adhesive to (using the side group).
How do you control cross linking rates of silanes
OH groups available
RH alters film forming ability, and ability to form strong network structure
How silanes can be used as coatings on inorganic materials
polymerised Si-O chains with hydrophobic side groups and an inorganic material that has lots of OH groups available, like silicon based stone (silicon dioxide).
These attract with hydrogen bonding between H-O
a bond between the silicon system and the inorganic material
Forming a hydrophobic layer on something which is not hydrophobic and would attract moisture, forming a water repelling sealant.
Silane-mineral reaction (diagram) also, what is an oligomer
a number of molecules joined together but less than a polymer, like 7 monomers
uses of silanes in industry
stops dampness/ moisture eg waterproof ribbons, electrics, stone coatings
MTMOS is a moisture barrier on stone
do not breathe it in
RTV silicone rubbers
set by reorganisation, not by losing a side group
