PLA looks like PET and forms like a fussy cousin of both. Use a dedicated or purged line such as LSI-120-36-900 or a PET/PLA twin-screw. Do not chase PLA on a dirty PP screw.
| Step | Typical window (resin-vendor band) |
|---|---|
| Predry | 4–6 h at 80–100°C, dew point about −40°C, moisture <250 ppm (prefer <100) |
| Melt / die | Often 170–210°C; avoid long residence above ~230–240°C |
| Chill rolls | Colder than PP; 25–40°C cited for amorphous sheet |
| Storage | Sealed rolls, form inside the supplier window |
Wet PLA hydrolyzes: melt pressure falls and cups crack at the rim. If sheet is brittle off the winder, lower roll temperature before you raise melt heat. Pair with an FS former that can hold a slow heat profile. See biodegradable extruders and send a PLA trial protocol with the RFQ.
What PLA is not
It is not backyard compost unless the grade and the market allow that claim. It is not a hot-fill tea cup. It is not cheaper than PP after freight and drying. Treat it as a contract resin: one hopper, one purge plan, one storage room.
Worked trial
Purge PP → run PLA 2 hours → check haze, gram weight, rim cracks. If gaylords sat open over a weekend, dry again; do not “try one hopper.” Starch blends use LSI-110-900, not a PET-only recipe.
Fault map — what the line is telling you
| Symptom | Likely cause | First check |
|---|---|---|
| Melt pressure falls mid-shift | Hydrolysis — moisture in the hopper | Close gaylords; re-dry 4–6 h toward <100–250 ppm |
| Sheet brittle off the winder | Rolls too warm; melt then over-cooked | Lower rolls first (25–40°C band), do not raise melt |
| Haze after a PP weekend | Dirty screw, not “bad PLA” | Purge; dedicated or fully cleaned line |
| Hot-fill tea cup fails in the field | PLA use ~55°C — not a PP substitute | Do not sell PLA as karak / coffee |
| Backyard-compost claim on the cup | Industrial EN 13432 / ASTM D6400 only unless grade allows | Print the standard you can prove |
RFQ checklist — send this in one email
Fill what you know; blank is better than a guess. Attach it on Get a Quote with photos of resin or flake.
- Grade and claimed standard (EN 13432 / ASTM D6400 / none)
- Tonnes for the trial vs ongoing contract
- Dryer dew point and whether a dedicated screw exists
- Former family (FS preferred for a stable heat profile)
- Storage: sealed room or open hall — be honest
Frequently asked questions
Is PLA compostable in a backyard?
Industrial composting (EN 13432 / ASTM D6400) is the usual claim. Do not print backyard compost unless the grade and the market allow it.
Can I blend PLA into PP?
Not as a silent drop-in. Compatibility and claims both break. Run dedicated recipes.
Why did melt pressure fall mid-shift?
Moisture. Close the hopper and re-dry.
FS or hydraulic for PLA cups?
FS holds a stable heat profile better. Either can form if the sheet is in window.