Lecture 7 - Plastics – Short Lecture Notes

Introduction to Plastics

• Core message from the lecturer: use plastics deliberately, not by default—always ask why you are choosing a plastic over alternative materials (glass, metal, timber, paper-based composites, etc.).

• Ethical undercurrent: beware of the environmental footprint, toxicity, and end-of-life implications of each polymer family before specifying it.

Historical Context

• First true plastics were invented as a substitute for ivory billiard balls.

  • Feedstock: casein (milk protein) hardened with formaldehyde.

  • Early example of a material innovation driven by shortage of natural resources and animal-welfare concerns—foreshadowing today’s sustainability debates.

• This origin story reminds designers that polymers were originally problem-solvers; they remain valuable when used to solve specific performance problems.

Common Sheet Plastics & Major NZ Supplier Websites

• Screenshots in lecture pulled from psp.co.nz (dominant architectural plastics distributor in New Zealand).

• Four headline sheet products on PSP’s catalogue page:

  • Acrylic (cast & extruded)

  • Polycarbonate

  • PVC sheets (including foam-cored PVC) – discouraged

  • ACM (Aluminium Composite Material) – primarily sign-writing/display

• Secondary supplier recommended for deeper research: Cactus Plastics (catalogues worth bookmarking for specs, thicknesses, colour charts, fire ratings, etc.).

Acrylic (Cast Acrylic / “Perspex”)

• Manufacturing method parallels float-glass casting; yields flat, optically clear sheets.

• Trade names you’ll meet in studio: Perspex, Plexiglas, Acrycast.

• Key properties & uses

  • High clarity; transmit ≈$92\%$ of visible light.

  • Good UV stability if UV-graded.

  • Laser-cuts cleanly (used daily on the school’s laser cutter).

  • Common applications: retail fit-outs, signage, POS displays, lightweight glazing where safety glass is over-spec.

  • Variety of finishes: clear, frosted, mirrored, decorative layers, and matte-tint ranges with vivid colours (useful for brand-specific palettes).

• Real-world significance

  • Favoured when glass weight, edge fragility, or shatter risk are unacceptable.

  • Recyclability depends on local streams; cast acrylic can often be re-melted, but infrastructure is patchy.

Polycarbonate Sheets

• Accepts laser cutting (with care against edge yellowing) and CNC routing.

• Two main architectural formats highlighted:

  1. Multi-wall / hollow-wall panels (twin, triple, X-structural cores).

  2. Solid square-section sheets.

• Performance notes

  • Excellent impact resistance (≈$250\times$ glass of same thickness).

  • Lightweight; density $\rho<em>{PC} \approx 1.2\;\text{g/cm}^3$ vs. $\rho</em>{glass} \approx 2.5\;\text{g/cm}^3$.

  • High heat-deflection temp (~$130\;^\circ\text{C}$) → can be cold-bent into shallow curves.

  • Translucent diffusion prized for daylight-harvesting skylights.

• Architectural uses observed in studio precedents:

  • Skylights, clerestories, interior light wells, sports-hall facades, and temporary pavilions.

PVC & Foam PVC Sheets

• Lecturer’s strong caution: avoid unless no alternative.

• The one defensible use case: downpipes, gutters where sunlight exposure would degrade other plastics.

• Why the reluctance?

  • Production and incineration release chlorine compounds and dioxins → significant health hazards.

  • Poor recyclability; mechanical recycling usually results in lower-grade products.

  • Tutor (Amina) flagged as “nasty, nasty product environmentally.”

• Architectural implication: specify PVC only when functional life-span, UV stability, and lack of substitutes outweigh environmental cost.

ACM (Aluminium Composite Material) & Shop-Fitting Plastics

• ACM sheet = aluminium skins bonded to polyethylene core; primary domain is signage and building wraps.

• PSP stocks diverse shop-fitting polymers (e.g., PET-G, HIPs) which sometimes migrate into small architectural elements (sneeze-guards, balustrades, secondary glazing).

• Tip: Evaluate whether a glass or metal equivalent can replace thin plastic for small-project conversions.

Kane Mail – Architectural Chain-Mail from Film Props

• Invented by a design student during Weta Workshop’s Lord of the Rings armour development.

• Material: interlinked polymer rings (lightweight, non-corroding).

• Evolved into façade/ceiling product sold under Kane Mail brand.

• Built example: University of Auckland building (grey variant visible in library stairwells).

• Demonstrates pathway from experimental film fabrication → commercial architectural material.

• Sustainability angle: check whether polymer type is recyclable, flame rated, and durable.

Sustainability, Toxicity & Recyclability Checklist

• Whenever you list a plastic in a specification schedule, annotate:

  • Raw polymer family (acrylic, polycarbonate, etc.).

  • Additives: UV stabilisers, flame retardants, plasticisers.

  • End-of-life path: mechanical recycling, chemical recycling, down-cycling, landfill.

  • Emissions during life-cycle (e.g., $\text{VOC}$ off-gassing, dioxins from PVC).

  • Possibility of swapping to glass, metal mesh, timber laminate, or bio-composite.

Lecture 7 - Plastics in Sustainable Construction

Plastics: Duality of Usefulness and Pollution

• Plastics simultaneously deliver indispensable functionality and impose severe ecological/health burdens.

  • Everyday convenience: packaging, hygiene products, building components.

  • Environmental toll: persistence, toxicity, greenhouse‐gas link, micro-/nano-plastic leakage.

  • Ethical tension: duty to preserve human well-being ↔ obligation to protect ecosystems.

Historical Illustration – Toothbrush Evolution

• Pre-plastic brushes

  • Handles: wood, bone.

  • Bristles: horse hair, plant fibres; fell out easily.

• Post-polymer revolution (DuPont, mid-$20^{\text{th}}$ century)

  • Cellulose acetate/nylon bristles solved shedding problem.

  • Example of plastics outperforming natural predecessors and accelerating consumer acceptance.

• Hidden polymer dependence extends to:

  • Brush handle.

  • Toothpaste tube (multi-layer laminates).

  • Toothpaste contents (thickening agents, microbeads).

Microplastics & Human-Environment Pathways

• Sources

  • Personal-care products (scrubs, pastes).

  • Laundry of synthetic clothing (e.g., polyester ≈ PET from bottles).

• Transport chain

  1. Domestic drain → wastewater → treatment overflow.

  2. Rivers → oceans → sediment & biota.

  3. Bioaccumulation → food web → human ingestion/ inhalation.

• Current discourse emphasises

  • <5\,\text{mm} fragments (micro), <1\,\mu\text{m} (nano).

  • Unknown long-term toxicology; precautionary principle urged.

Exponential Growth of Synthetic Chemicals

• Author’s decade-long data compilation shows two coupled exponentials:

  1. Newly invented chemicals per year.

  2. Total chemicals catalogued.

• Starting baseline: $2.5\times10^{5}$ chemicals; contemporary registry >$1\times10^{7}$.

• Gaps in datasets illustrate monitoring difficulty & regulatory lag.

Knowledge Gaps in Health Assessments

• High-Production-Volume (HPV) chemicals: $\ge1\,000\,000$ t yr$^{-1}$.

  • Only $10\text{–}20\%$ possess even minimal toxicological dossiers.

  • Therefore life-cycle assessments (LCAs) rest on a “$90\%$ unknowns” substrate.

• For construction sector, $95\%$ of chemicals lack sufficient evaluation → industry-wide experiment on workers, occupants, ecosystems.

Hydrocarbons: Universal Feedstock for Plastics

• Fossil basis

  • $90\%$ of synthetics derive from petroleum/natural gas.

  • Yet only $10\%$ of fossil extraction feeds chemical sector (rest ≈ fuel).

• Standard monomers (all colourless, flammable, often heavier than air):

  • Ethylene, propylene, styrene, vinyl chloride, etc.

• Production mechanics

  • Steam cracking at >800\,^{\circ}!\text{C}.

  • Tall stacks for heat/venting; by-product “coke” concentrates radio-nuclides.

• Occupational hazards: explosions, fires (case studies during COVID-19 reduced staffing).

Polyethylene (PE) – Relatively Benign Option

• Chemistry

  • Ethylene $\rightarrow$ PE via chain growth polymerisation.

  • Variants: LDPE (linear, low density), HDPE (branched, higher density), XHDPE.

• Architectural applications

  • HDPE water tanks, potable-water pipes (safer than PVC).

  • Geomembranes & damp-proof courses.

  • Recycled bag lumber, decking.

• Recycling codes:

  • HDPE = #2, LDPE = #4 (widely collected; #2 > #4 in recovery rate).

Other Major Construction Plastics

• Polyethylene terephtalate (PET / polyester)

  • Bottles, insulation batts, carpets; recycling code #1; moderate circularity.

• Polypropylene (PP) – #5

  • Plumbing, food tubs, door-mat carpets; dangerous monomer (propylene); poor post-consumer recovery.

• Polystyrene (PS = #6)

  • EPS/XPS insulation boards, disposable trays; low density → litter/marine issues.

• Styrene-Acrylonitrile (SAN), Acrylonitrile-Butadiene-Styrene (ABS)

  • Sockets, appliance housings; difficult to recycle.

• Polycarbonate (PC = part of #7)

  • Transparent roofing, bus windows; synthesised from Bisphenol-A (BPA) – potent endocrine disruptor.

• Polyvinyl chloride (PVC = #3) – see dedicated section.

Relative Safety Colour-Code (author’s synthesis)

• Yellow = potentially low hazard (PE).

• Orange = moderate (PET, PP) – watch processing fumes & additives.

• Red = high (PS, SAN/ABS).

• Dark-red/Black = severe (PC, PVC).

End-of-Life Considerations

• Combustion

  • Energy recovery possible; releases HCl (PVC), dioxins, PAHs → respiratory/carcinogenic.

• Biodegradation

  • Many polymers exceed $100$ yrs; first to leach = additives (phthalates, flame retardants).

• Additive toxicity example

  • Phthalates in PVC flooring: endocrine disruption, developmental risk.

Biopolymers & Emerging Alternatives

• Concept: extract identical monomers from biomass (corn, sugarcane) instead of fossils.

• Polylactic acid (PLA)

  • Compostable under >60\,^{\circ}!\text{C},\;>0.6\,\text{MPa} industrial settings.

  • Frequently blended with wood dust to enhance degradability.

  • Food vs. material conflict: corn fuel fiasco illustrated socio-economic risk.

• Need for full LCA: land use, fertiliser run-off, social equity.

Three-Stage Recognition & Elimination Framework (Kuzmanović, PhD)

1. Stage I – Hazard Recognition

   • Initial scientific/red-flag signals.

2. Stage II – Regulation & Control

   • Occupational limits, bans, labelling.

3. Stage III – Elimination/Substitution

   • Market exit & toxic-legacy management.

• Evaluation findings

  • Lead & asbestos: partially eliminated, but remediation ongoing ⇒ no true success story.

  • Current “hot” hazards (formaldehyde, phthalates) not being phased-out faster than historical precedents.

  • New substances introduced without pre-market testing → perpetual backlog.

Polyvinyl Chloride (PVC) – Deep Dive

• Market share: 3rd­-largest polymer globally; $60\%$ consumed by construction.

• Forms

  • uPVC (rigid): pipes, window frames.

  • pPVC (plasticised): flooring, cables, wallpapers, food trays.

• Synthesis chain

  1. Ethylene + Chlorine $\rightarrow$ Ethylene dichloride (EDC).

  2. Pyrolysis of EDC $\rightarrow$ Vinyl chloride monomer (VCM) – volatile anaesthetic candidate in $1930$s; chronic exposure now linked to angiosarcoma of liver.

  3. Polymerisation $\rightarrow$ PVC powder.

  4. Compounding with stabilisers (lead, cadmium, organotin), plasticisers (phthalates), pigments, fillers.

• Process hazards

  • Mercury-cell electrolysis (older route) → Hg contamination.

  • Asbestos diaphragm technology.

  • Explosions/fires: highly chlorinated smoke.

• Recycling issues

  • Code #3 rarely accepted; presence of heavy-metal stabilisers complicates melt processing.

  • Continuous re-smelting = worker/community exposure (case of NZ pilot plant).

• Regulatory status

  • EU debating lead-free pipe mandate only in $2015$.

  • Food-contact PVC still present (clear trays); consumer boycott recommended.

Connections to Previous Lecture (Life-Cycle Analysis)

• LCA comparison of reusable vs. disposable cups relied on databases missing $90\%$ toxicity data ⇒ results tentative.

• Highlighted need to integrate chemical hazard weightings into carbon/energy metrics.

Practical Implications for Architects & Specifiers

• Prioritise materials with:

  • Well-characterised toxicology (PE, some PET).

  • Established, transparent recycling streams.

  • Low additive content; specify additive-free where performance allows.

• Avoid/limit

  • PVC (especially pPVC), PC, brominated flame-retardant plastics.

  • Composite systems that block future separation.

• Demand supplier disclosure: Safety Data Sheets (SDS), Red-List compliance, EPDs with chemical inventory.

• Incorporate precautionary principle in material selection and client education.

• Recognise indoor curing of paints, sealants as in-situ polymerisation; schedule ventilation accordingly.

• Engage in material research/advocacy to shrink the “unknown $90\%$.”

Ethical & Philosophical Reflections

• Society is conducting an uncontrolled experiment on humans & ecosystems.

• Rapid innovation without commensurate safety assessment challenges sustainability, equity, and precautionary ethics.

• Architects hold gatekeeping power: every specification influences chemical demand and, by extension, production, exposure, and waste patterns.