MEEN 223 Polymer Processing

PE – Polyethylene

Most widely produced plastic (≈ 34 wt % of global market). Cheap, tough, chemically inert; dominates packaging (film, bottles)

PP – Polypropylene

Versatile low-density thermoplastic; good fatigue (living hinge) and heat resistance. Common in food tubs, caps, automotive trims (fact of use added for clarity; slide listed as example).

PVC – Polyvinyl Chloride

Rigid (pipe, profiles) or plasticized-flexible (cable jackets). Naturally flame-retardant due to chlorine content.

PMMA – Poly(methyl methacrylate) (acrylic)

Transparent, weather-resistant “glass” replacement; signs, lenses, aquaria.

PS – Polystyrene

Brittle but clear (rigid PS) or foamed into light insulating EPS (coolers, cups).

Common Engineering Plastics

• ABS – tough, easily molded (e.g., LEGO).

• Nylon (6/6-6/12) – strong, wear-resistant; fibers, gears.

• PET – beverage bottles, fibers.

• PC (Polycarbonate) – high impact transparency (head-lights).

• PEEK – high-temperature, chemical-resistant aerospace parts. ​

(Full slide list included ABS, PA, PBT, PI, POM, PPS, PPO, PSU, PTFE).

Polymer

Giant molecule of repeated units (10 k – 1 M g mol⁻¹), usually hydrocarbon-based. ​

Polymerization

Chemical joining of monomers/oligomers into long chains. ​

Plastics

Polymers + additives (fillers, pigments, fibers).

Thermoplastic

Polymer that softens/melts on heating and can be remolded; recyclable; good impact toughness.

Thermoset

Polymer that cross-links irreversibly during curing; cannot be remelted; superior heat/chemical resistance & finishes.

Elastomer

Lightly cross-linked polymer that can stretch and recover (rubber).

Extrusion

Continuous screw forces molten thermoplastic through a shaped die.

Pipe, tubing, film, sheet, profiles.

High throughput, uniform cross-section, low part cost.

Limited to constant-section parts; tooling changes = downtime.

Injection Molding

Screw plasticizes pellets then injects melt into a cooled metal mold to solidify.

Complex 3-D parts in high volumes (caps, housings).

Excellent repeatability & surface finish; fast cycle.

Very high mold cost/lead-time; less economical for low volume.

Tooling (for both)

Hardened tool steel molds, quenched for wear-resistance; labor-intensive hand polishing; long lead and expensive but long service life.

—

Durable, tight tolerances.

Costly & slow to build.

Vacuum Thermoforming

Heat plastic sheet until soft, drape over mold; vacuum through holes pulls sheet into cavity.

Food trays, disposable cups, dashboards.

Pressure Thermoforming

Same heat step, but compressed air (or matched top mold) pushes sheet onto detailed mold for better definition.

Refrigerator liners, large panels.

Blow Molding

Inflate a hot parison inside closed mold → hollow bottles, fuel tanks.

Compression Molding

Place thermoset charge in heated cavity, close & cure under pressure → electrical connectors, automotive composites. ​

Dip Molding

Dip form into liquid latex/synthetic rubber, withdraw, then vulcanize (cross-link) → gloves, balloons.

Fiber-Reinforced Composite (FRC)

High-strength, lightweight material made of stiff fibers (carbon, glass) embedded in polymer matrix; used in bikes, aircraft, cars. ​

RTM – Resin Transfer Molding

Close dry-fiber preform in matched mold, inject low-viscosity thermoset, cure under heat/pressure; good surface finish & dimensional accuracy.

VIP – Vacuum Infusion Process

Lay dry fabric on open tool, cover with vacuum bag, draw resin through fibers via vacuum; cheaper tooling than RTM, longer fill times. (concept not pictured but industry-standard variant).

VARTM – Vacuum-Assisted RTM

Hybrid: rigid lower mold + flexible vacuum bag top; resin drawn by vacuum (no high-pressure pumps), then oven-cured; widely used for large wind-turbine blades.

The “Big Four” Comparison (Metrics to weigh any manufacturing option)

• Quality – achievable part precision & surface finish.

• Cost – tooling + per-part cost (economies of scale).

• Rate – production throughput (parts / time).

• Flexibility – ease of design changes & variety of shapes.

Injection Molding “Big Four”

Quality = Good, Cost = Low (when high-volume), Rate = High, Flexibility = Low (expensive tooling).

Thermoforming “Big Four”

Quality = Lower, Cost = Less at low volume, Rate = Higher, Flexibility = Greater (cheaper tooling). ​

Plastic Manufacturing Processes

Extrusion
Injection Molding
Tooling (for both)

Thermoforming

Vacuum Thermoforming
Pressure Thermoforming

Other Molding Routes

Blow Molding

Compression Molding
Dip Molding

Composite Material Processing

Fiber-Reinforced Composite (FRC)
RTM – Resin Transfer Molding
VIP – Vacuum Infusion Process
VARTM – Vacuum-Assisted RTM