Processing And Manufacture Flashcards
What is polymer processing?
- conversion of raw material / compound into a finished / semi-finished part
- includes mixing / compounding
What is the exceptions to polymerisation being a part of processing?
- ‘reaction processes’ (e.g. graft copolymers)
- curing / crosslinking (rubbers and thermosets) also involves chemical
reactions)
Why is there an increase in demand in the use of polymers?
- Environment and sustainability
2.More markets; increased consumer acceptance
Higher quality & component reliability; improved quality assurance (QA)
Innovation by design & process novelty
Sustainable / recyclable products – despite recent media attention !
More effective and low-energy manufacturing / processing (AM – MPD014)!
What are the objectives of processing?
How important of the processing related to both the structures and properties of polymers and industry?
Structures relate to the molecular structure(chain length, branching), the crystallinity(from amorphous to crystalline), morphology(controlling movement of polymer chains) and additives (UV resistance, pigment, flame ratrdents)
These properties can be added at the manufacturers discretion as well as their choice in processing techniques, sustainability and cost efficiency which will determine is the performance is sufficient.
What are the differences between the processing of thermoplastics, thermosets and rubbers?
Structurally Thermoplastics are linear or branched whereas both thermosets(permanent) and rubbers(highly flexible) are cross linked.
Only thermoplastics and rubbers (through vulcanisation) can be re moulded or reformed. And thermoplastics have a moderate heat resistance whereas thermosets and rubbers have high resistance.
What is the simple cost model for processing?
Of the total product cost it is 30% material cost, 50% process costing (labour, output, cycle time), 10% overheads(fixed) and 10% profit(want to increase this)
What are the 3 main flow (rheological) properties?
Shear viscosity, shear stress and shear strain rate.
What is a pseudoplastic fluid?
A fluid that increases in viscosity as more force is applied. This is dependent on the power law model (cite eqaution) and the newtonian model
What flow property is shear rate dependent on?
viscosity
What are the 3 main processes for thermoplastics? and what are examples of each?
1.Melt state processes(Extrusion / injection moulding / blow moulding / rotational moulding / compression moulding / calendering),
2.heat softening(Thermo-(vacuum) forming / orientation processes, including stretch blow moulding (biaxial - bottles) / film (biaxial) / fibres (uniaxial)) processes or
3.miscellaneous (Processing in solution or paste / monomer casting (PMMA) / polymer foams).
What is the main process of processing thermoplastics?
Polymer + additives = compound.
The raw compound is melted (undergoing phase change), then it can be shaped and cooled to form the product.
What is the phase change ability dependent on ? and what are examples of this?
- thermal properties - conductivity, expansion, enthalpy, transitions.
- flow characteristics - viscosity, temperature/pressure, molecular weight, strain/shear rate, shear/elongational flow
What are thermosetting plastics ? Name the difference between thermoset and thermoplastics.
Thermosets when they undergo heat and hardening they create crosslinks withing the plastics they are incredibly hard to break.
What are the main characteristics for thermosetting plastics?
Flow, followed by cure
High crosslink density
High glass transition (Tg)
(rigid at ambient temperature)
Use of catalysts
What are the main 3 processes for thermosetting plastics? name the examples of each
- Moulding Techniques (including curing) - Injection moulding / transfer moulding / compression ‘hot-press’ moulding / reaction injection moulding (RIM)
2.Lamination / composites processes
-Many processes are available to impregnate reinforcing fibres (glass, carbon) with liquid thermoset resins
3.Miscellaneous -
Use of thermosets as adhesives, surface coatings, paints
Liquid resin casting
Thermoset foams
What is the main process of processing thermosets?
Taking the raw compound it is mixed, heated, shaped, chemical reaction forms a solid and it is cooled.
What are the characteristics of elastomers/rubbers?
Crosslinked network:
Permanent molecular structure
Low crosslink density
Materials is at T>Tg, at ambient temperature, hence “rubber”
Kinetics of curing:
Chemical reaction – temperature dependent
Onset and rate of cure – controlled by additives (activators, accelerators)
What is the process of making elastomers/ rubber?
With raw rubber material additives are added to be mixed in primary process (mixing) as well as mastication (softening molecular chains mechanically), then it is shaped and crosslinked to produce a finished product. Finishings can take place next.
What are some main applications of polymers?
Energy materials, fuel cell application(low emissions, high efficiency, low noise and simplicity), MEA (membrane Electrode Assembly), PEM (polymer electrolyte membrane)- good chemical stability or higher conductivity but -ves is it is a high cost, high crossover rate with methanol)
What are the differences between the properties of thermoplastics, thermosets and rubbers?
Thermoplastics are flexible, easy to process and recyclable.
Thermosets are rigid, heat resistant and durable.
Rubbers are Elastic, flexible, durable (with vulcanization).
What are monomers?
A single molecule. It becomes a polymer when there is many linked chains.
What is vulcanisation?
process of cross linking molecules chemically with other substances under pressure and temperature conditions.
