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Material · Synthetic

PLA

Made from sugar rather than oil, and compostable in an industrial composter and almost nowhere else.

PLA is made by fermenting plant sugar — usually maize or sugarcane — to lactic acid and polymerising that. Its carbon comes from the atmosphere within the last growing season rather than from a geological reservoir, which is a real distinction and a narrower one than the marketing around it suggests.

As a material it is stiff, strong, glossy and brittle, with a low softening point near 60 °C. That last figure is the constraint that shapes every use: a PLA cup deforms with hot coffee in it and a PLA part left in a car in summer sags.

It is the default desktop 3D printing filament because it prints easily, barely warps, needs no heated chamber, and smells faintly sweet rather than of hot solvent.

Processing

Injection moulded, extruded into film and filament, and thermoformed, all on conventional equipment at moderate temperatures — which is a large part of its commercial appeal, because a converter needs no new machinery.

It is sensitive to moisture at melt temperature: wet PLA hydrolyses in the barrel and the product is weak and stringy, so it is dried before processing. This is the same failure mode as PET and for the same chemical reason.

Uses

3D printing filament, where it dominates the desktop market. Food service disposables — cups, cutlery, salad boxes — and packaging film. Teabags and coffee capsules. Agricultural mulch film.

In medicine it is genuinely load-bearing and genuinely temporary: resorbable sutures, pins and screws that hydrolyse harmlessly over months and remove the need for a second operation to take the hardware out. This is the application where its degradability is unambiguously the point.

History

The polymer was known from the 1930s and impractical: it was expensive and it degraded, which were two ways of saying the same thing. Medical use came first, in the 1970s, precisely because degrading was the requirement.

Commodity production dates from Cargill's work in the 1990s and the NatureWorks plant that opened in 2002, which brought the price within reach of packaging by scaling the fermentation rather than by changing the chemistry.

Environmental impact

The honest summary is that PLA is compostable under conditions most waste does not encounter. It needs sustained temperatures around 58 °C and controlled humidity — an industrial composting facility. In a home compost heap it persists for years; in the sea it persists; in landfill it persists and, if it does break down anaerobically, produces methane.

In a recycling stream it is a contaminant. PLA and PET are visually and near-infrared similar enough to be mis-sorted, and PLA in a PET recycling batch degrades the whole lot, which is a real and documented cost imposed by a material sold as the environmental option.

What is genuinely true: the carbon is biogenic, production emits substantially less than the equivalent oil-derived polymer, and the feedstock is renewable. What is not: that it disappears if dropped. Both halves matter, and the second is the one usually left out.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

contains

  • Carbon — element · the backbone, and it came out of the atmosphere within the last growing season rather than out of the ground
  • Hydrogen — element · the balance
  • Oxygen — element · in the ester links — and the reason it hydrolyses, which is both the resorbable suture and the compostability claim

is produced by

  • Polymerisation — process · ring-opening polymerisation of lactide, itself made by fermenting plant sugar to lactic acid

is used as

  • Additive manufacturing — application · the default desktop filament: it prints easily, barely warps, and softens near 60 °C, which is the limit on what it can be used for
  • Packaging — application · food service disposables and film, sold on compostability that requires an industrial composter to deliver

is an alternative to

  • Polypropylene — material · in disposables, and the substitution is not like for like: PLA softens near 60 °C, so it cannot hold a hot drink or survive a dishwasher
  • Polyethylene terephthalate — material · as packaging film and rigid containers — and PLA is a contaminant in the PET recycling stream, which is a real cost the substitution imposes elsewhere
  • Crude oil — material · as the origin of a polymer's carbon — plant sugar rather than a geological reservoir, which is a genuine distinction and a narrower one than the marketing suggests

is commonly confused with

  • Polyethylene terephthalate — material · similar enough in appearance and in near-infrared sorting to be mis-sorted, and PLA in a PET recycling batch degrades the whole lot

is used in

  • Medical devices — industry · resorbable sutures, pins and screws, where degrading is the requirement rather than the drawback

belongs to the group

  • Plastic — material · made from plant sugar, and compostable in an industrial composter and almost nowhere else

Sources

  • Material World
    Our own writing
  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)

Questions this page answers

Where it comes from, and what it becomes

Follow PLA back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • PLA → is produced by (ring-opening polymerisation of lactide, itself made by fermenting plant sugar to lactic acid) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as the brine the cell electrolyses, and as the source of the hydrogen that comes off the cathode) → Water → is sourced from (by desalination, where energy is cheap and coastline available — the only route that adds fresh water rather than moving it) → Seawater
  • PLA → is produced by (ring-opening polymerisation of lactide, itself made by fermenting plant sugar to lactic acid) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is produced by (electrolysis of potassium bifluoride, which is molten and conducts — there is no chemical oxidant strong enough to displace fluorine from a compound, so electricity is the only route and always has been) → Molten salt electrolysis → takes as input (after concentration, as one of the two routes to lithium chloride) → Lepidolite
  • PLA → is produced by (ring-opening polymerisation of lactide, itself made by fermenting plant sugar to lactic acid) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is extracted from (by electrolysis of brine, which yields chlorine and sodium hydroxide together) → Halite
  • PLA → is produced by (ring-opening polymerisation of lactide, itself made by fermenting plant sugar to lactic acid) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is extracted from (the only significant source; hydrofluoric acid is made from it and everything fluorinated follows) → Fluorite
  • PLA → is produced by (ring-opening polymerisation of lactide, itself made by fermenting plant sugar to lactic acid) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (the largest single use of salt, and the process the whole chlorine and caustic soda industry rests on) → Salt → is produced by (in the solar route — the same process, read from the other end) → Brine evaporation
  • PLA → is produced by (ring-opening polymerisation of lactide, itself made by fermenting plant sugar to lactic acid) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite

These are the most distinct paths back. PLA can be traced through others besides.

Downstream — what it becomes

  • PLA → is used as (the default desktop filament: it prints easily, barely warps, and softens near 60 °C, which is the limit on what it can be used for) → Additive manufacturing
  • PLA → is used as (food service disposables and film, sold on compostability that requires an industrial composter to deliver) → Packaging
  • PLA → is used in (resorbable sutures, pins and screws, where degrading is the requirement rather than the drawback) → Medical devices