Chem Commodity Engineering Plastics Additives And Processing

---
name: chem-commodity-engineering-plastics-additives-and-processing
description: "Use when selecting or troubleshooting a plastic: the commodity plastics and what each is actually for, engineering and high-performance polymers, additives including plasticizers, stabilizers, fillers and flame retardants, elastomers, thermosets and composites, processing by extrusion, injection moulding, blow moulding and thermoforming, and degradation and failure including environmental stress cracking and UV and thermal ageing."
---

# Organic Chemistry and Plastics: The Commodity Plastics, Engineering and High-Performance Polymers, Additives, Elastomers, Thermosets and Composites, Processing, and Degradation and Failure

> **Part 4 of 6** of the *Organic Chemistry and Plastics Engineering* reference (plugin `organic-chemistry-and-plastics-engineering`), covering §18–§23. Sibling skills: `chem-carbon-bonding-functional-groups-and-stereochemistry` (§0–§5), `chem-mechanisms-reactions-characterization-and-synthesis` (§6–§12), `chem-polymers-polymerization-molecular-weight-and-morphology` (§13–§17), `chem-recycling-bioplastics-and-health-regulation` (§24–§26), `chem-reference` (§27–§32). Section numbers are shared across the set; a reference written as §N → `skill` points into that sibling skill.
>
> **Currency:** The chemistry is settled. Two regulatory areas are moving. See §27 → `chem-reference` for the global plastics treaty, and the EU PFAS restriction.

> **⚠️ Two disciplines joined at one hinge: organic chemistry explains what molecules DO,
> and polymer engineering explains what happens when you make them very long.** ⚠️ **Chain
> length changes almost everything — a C₂₀ hydrocarbon is a wax and a C₂₀₀,₀₀₀ one is a
> structural material, with identical chemistry.**
>
> **Complements a manufacturing reference (moulding and processing), a materials/textiles
> reference (fibres and finishing), and a thermodynamics reference (phase behaviour).**
>
> **⚠️ SCOPE NOTE: this is a conceptual map of mechanisms, materials and industrial
> practice. It is not a laboratory manual and contains no procedures.** ⚠️ **Practical
> synthetic work requires trained supervision, proper facilities and hazard assessment —
> organic chemistry involves flammables, toxics, corrosives and exotherms that hurt people
> who improvise.**
>
> **⚠️ GOTCHA** boxes mark where intuition fails and where products actually break.
>
> **The three ideas that organize this document:**
> 1. **⚠️ STRUCTURE DETERMINES PROPERTIES, through mechanism** (§3 → `chem-carbon-bonding-functional-groups-and-stereochemistry`, §6 → `chem-mechanisms-reactions-characterization-and-synthesis`). **Functional
>    groups are behaviour classes, and reaction "rules" are consequences of electron
>    density and sterics rather than facts to memorize.**
> 2. **⚠️ Tg AND MORPHOLOGY GOVERN PLASTIC BEHAVIOUR more than chemistry does** (§16 → `chem-polymers-polymerization-molecular-weight-and-morphology`).
>    **Whether a polymer is rigid, rubbery, tough or brittle at your service temperature
>    follows from where Tg sits and how much crystallinity there is.**
> 3. **⚠️ Most plastic FAILURES are environmental, not mechanical** (§23). **Environmental
>    stress cracking, UV, and additive migration destroy far more parts than overload
>    does — and the load that causes ESC is often well below the design stress.**

---

## §18. The Commodity Plastics

```
⚠️ PE  ⚠️ HDPE (linear, crystalline, stiff — bottles, pipe) ·
   LDPE (branched, soft, film) · LLDPE · UHMWPE (⚠️ extraordinary
   abrasion resistance and impact, hard to process)
⚠️ PP  ⚠️ isotactic (§13). Higher Tm than PE, ⚠️ excellent LIVING
   HINGE behaviour, ⚠️ but Tg near or above 0 °C so it embrittles
   in cold — a very common in-service failure
⚠️ PVC  ⚠️ rigid (pipe, window frames) or flexible depending
   ENTIRELY on plasticizer content (§20). ⚠️ Contains chlorine,
   which complicates incineration and recycling
⚠️ PS  ⚠️ cheap, clear, BRITTLE (Tg ~100 °C, so glassy at room
   temperature). ⚠️ HIPS and ABS are rubber-toughened versions
⚠️ PET  ⚠️ bottles and fibre. ⚠️ Crystallizes controllably (§16),
   ⚠️ and HYDROLYSES if processed wet — drying before moulding is
   mandatory, not optional
⚠️ PU  polyurethanes — foams, coatings, elastomers. Enormously
   versatile family
```
**⚠️ These six or so families dominate volume overwhelmingly** — ⚠️ **the exotic materials
in §19 are a small fraction of tonnage and a large fraction of the literature.**

---

## §19. Engineering and High-Performance Polymers

⚠️ **NYLONS (PA6, PA66) — tough, abrasion-resistant, ⚠️ and HYGROSCOPIC: they absorb water
which acts as a plasticizer, so properties shift with humidity and parts change dimensions.
⚠️ This is a classic design trap.**
**⚠️ POLYCARBONATE** — ⚠️ **exceptional impact toughness and transparency; notch-sensitive;
attacked by many solvents** (§23).
**⚠️ POM/acetal** — ⚠️ **stiff, low friction, excellent dimensional stability; gears and
bearings.**
**⚠️ PBT, PPS, PEI, PSU, PPO** — ⚠️ **increasing thermal and chemical performance.**
**⚠️ PEEK** — ⚠️ **semi-crystalline, high Tg and Tm, outstanding chemical and radiation
resistance; expensive and demanding to process.**
**⚠️ FLUOROPOLYMERS (PTFE, FEP, PFA, ETFE, PVDF)** — ⚠️ **the C–F bond is exceptionally
strong, giving near-universal chemical inertness, thermal stability and the lowest
coefficients of friction available.** ⚠️ **PTFE is not melt-processable in the ordinary
sense and is sintered.** **⚠️ These are also the materials at the centre of §27.2 → `chem-reference`.**
**⚠️ The general pattern**: ⚠️ **performance tracks aromatic content, chain stiffness and
polarity — and so does price and processing difficulty.**

---

## §20. ⚠️ Additives

> **⚠️ A commercial plastic is a FORMULATION, not a polymer. The additives frequently
> determine performance, cost, regulatory status and failure mode.**
```
⚠️ PLASTICIZERS  ⚠️ lower Tg by getting between chains. ⚠️ Flexible
   PVC can be a large fraction plasticizer by weight
   ⚠️ THEY MIGRATE OUT over time — which is why old vinyl goes
   stiff and cracks, and why migration is a health question (§26)
⚠️ STABILIZERS  ⚠️ antioxidants (⚠️ consumed over time — stabilizer
   depletion is a real end-of-life mechanism) · UV absorbers and
   HALS · heat stabilizers (⚠️ essential for PVC, which
   autocatalytically dehydrochlorinates when hot)
⚠️ FILLERS and REINFORCEMENT  ⚠️ glass fibre transforms stiffness
   and strength and makes properties ANISOTROPIC and dependent on
   flow direction · talc, carbon black, calcium carbonate
⚠️ FLAME RETARDANTS  ⚠️ historically a significant environmental and
   health problem; brominated types are heavily restricted
⚠️ PIGMENTS · lubricants and processing aids · antistatics ·
   nucleating agents · impact modifiers · blowing agents
```
**⚠️ Additives are why recycling is hard** (§24 → `chem-recycling-bioplastics-and-health-regulation`) — ⚠️ **a recycled stream has unknown
formulation, depleted stabilizer and mixed additive chemistry.**

---

## §21. Elastomers, Thermosets and Composites

**⚠️ Elastomers** are ⚠️ **lightly crosslinked polymers used ABOVE their Tg, and their
elasticity is ENTROPIC — stretching a chain reduces its conformational entropy, and the
retractive force is the drive to regain it.** ⚠️ **A stretched rubber band heats up, which
is the everyday demonstration.**
**⚠️ Vulcanization** (sulfur crosslinking of natural rubber) ⚠️ **is the transformation that
made rubber a usable material.**
**⚠️ Thermoplastic elastomers** achieve rubber behaviour WITHOUT chemical crosslinks —
⚠️ **block copolymers whose hard domains act as physical crosslinks that melt on heating,
so they're processable and recyclable** (§13 → `chem-polymers-polymerization-molecular-weight-and-morphology`).
**⚠️ Thermosets** (epoxy, phenolic, unsaturated polyester, some PU) — ⚠️ **cured
irreversibly, with excellent thermal and dimensional stability, and no melt route back.**
**⚠️ Composites**: ⚠️ **fibre carries load, matrix transfers it, and THE INTERFACE governs
performance — which is why sizing and surface treatment of fibres matters more than people
expect.** ⚠️ **Properties are highly anisotropic and layup-dependent.**

---

## §22. Processing

**⚠️ See a manufacturing reference for moulding design rules.** ⚠️ **The polymer-specific
points:**
⚠️ **melt rheology is SHEAR-THINNING, which is what makes injection moulding possible at
all; ⚠️ molecular ORIENTATION is frozen in during flow and makes parts anisotropic;
⚠️ RESIDUAL STRESS from differential cooling drives warpage and later stress cracking
(§23); and ⚠️ THERMAL HISTORY matters — every heat cycle degrades the polymer slightly,
which is directly why recyclate has lower properties** (§24 → `chem-recycling-bioplastics-and-health-regulation`).
**⚠️ Drying before processing is mandatory for hygroscopic and hydrolysis-prone resins**
(PET, PA, PC) — ⚠️ **wet processing permanently cuts molecular weight and the part is
weak with no visible defect.**

---

## §23. ⚠️ Degradation and Failure

> **⚠️ Most plastic parts do not fail by being overloaded. They fail environmentally, and
> the first item below is the one that surprises engineers.**
```
⚠️ ENVIRONMENTAL STRESS CRACKING (ESC)  ⚠️ THE most under-appreciated
   plastic failure mode. ⚠️ A polymer under tensile stress —
   including RESIDUAL stress from moulding (§22) — cracks in
   contact with a fluid that would be harmless alone, at a stress
   FAR BELOW its normal strength
   ⚠️ Classic pairings: PC with certain solvents and even some
   cleaning agents; PE with detergents and surfactants
   ⚠️ It is not chemical attack — the agent promotes craze growth
   ⚠️ Mitigate by: reducing residual stress (annealing, gate and
   cooling design), avoiding the agent, material selection
⚠️ UV / PHOTO-OXIDATION  ⚠️ chain scission and crosslinking;
   chalking, yellowing, embrittlement. ⚠️ Carbon black is the
   cheapest effective UV screen, which is why outdoor plastics
   are so often black
⚠️ THERMAL OXIDATION  ⚠️ accelerates once antioxidant is consumed
⚠️ HYDROLYSIS  ⚠️ attacks ester and amide backbones — PET, PC, PA,
   PU. ⚠️ Temperature and humidity dependent
⚠️ CHEMICAL ATTACK, SWELLING and PLASTICIZATION by absorbed fluid
⚠️ CREEP RUPTURE (§17) · fatigue · wear · ⚠️ additive migration (§20)
```
**⚠️ Failure analysis**: ⚠️ **read the fracture surface — brittle fracture shows a mirror,
mist and hackle pattern radiating from the initiation site; ductile failure shows drawing;
ESC shows multiple crazes.** ⚠️ **The initiation point almost always tells you the cause.**