Industrial Chemistry: MDCAT Notes and MCQs
Adhesives
Substances that bind two surfaces together.
- Natural: starch/dextrin (paper, envelopes), animal glue (from collagen — bones, hides), casein (milk protein), natural rubber.
- Synthetic:
- Thermosetting resins: epoxy resins (two-part, very strong — metals, ceramics, aircraft), phenol-formaldehyde, urea-formaldehyde (plywood).
- Thermoplastic: polyvinyl acetate (PVA — "white glue" for wood/paper), hot-melts.
- Cyanoacrylates ("super glue" — instant; also used to close wounds).
- Elastomers/contact adhesives (neoprene, rubber cement), pressure-sensitive adhesives (tapes, labels).
Dyes
Coloured compounds that attach to fibres. Colour arises from chromophores (–N=N–, –NO2, C=O); auxochromes (–OH, –NH2) deepen colour and help binding.
| Type (by application) | Features / uses |
|---|---|
| Acid dyes | Anionic; wool, silk, nylon |
| Basic (cationic) dyes | Acrylics, silk; e.g. methylene blue |
| Direct dyes | Applied directly to cotton in aqueous solution (e.g. Congo red) |
| Mordant dyes | Need a mordant (metal salt, e.g. alum) to fix — alizarin |
| Vat dyes | Insoluble; reduced to soluble form, then oxidized on fibre — indigo (denim) |
| Disperse dyes | Polyester, acetate fibres |
| Azo dyes | Contain –N=N–; largest class (methyl orange) |
| Reactive dyes | Form covalent bonds with cotton — very fast colours |
Polymers
- Addition (chain-growth) polymers: monomers with C=C add without losing any molecule; polymer has same empirical formula as monomer.
- Polyethylene/polythene (ethene), PVC (vinyl chloride), polystyrene (styrene), Teflon (tetrafluoroethene — non-stick), polyacrylonitrile/Orlon (acrylonitrile), polypropylene, synthetic rubber.
- Condensation (step-growth) polymers: monomers with two functional groups join with loss of a small molecule (H2O, HCl, CH3OH).
- Polyamides: nylon-6,6 (hexamethylene diamine + adipic acid). Polyesters: terylene/Dacron (PET) (ethylene glycol + terephthalic acid). Phenol-formaldehyde (bakelite), melamine-formaldehyde, epoxy resins. Natural: proteins, cellulose, starch.
- Sub-types: homopolymer (one monomer — polythene) vs copolymer (two monomers — nylon-6,6, SBR); thermoplastics (soften on heating, recyclable — PVC, polythene) vs thermosetting (cross-linked, set permanently — bakelite, melamine).
PMDC learning outcomes for this unit
- Adhesives, dyes, polymers: 20.1 Know about types and application of adhesives.
- Adhesives, dyes, polymers: 20.2 Know about types of dyes and their uses.
- Adhesives, dyes, polymers: 20.3 Know about condensation and addition polymers and their sub-types.