Bio Based TPU Film and How Bio Content Changes Performance
Feedstock, Mass Balance and the Properties That Shift
Bio based TPU film is not the same thing as biodegradable TPU film, and confusing the two causes specification errors that only appear after the product is in service. Bio based describes where the carbon came from, while biodegradable describes what happens at end of life.
A bio based TPU is still a durable thermoplastic, and it will not break down in soil any faster than a petrochemical one.
This article covers what the bio content actually replaces, how it is measured and claimed, and which properties move when part of the carbon comes from plants.
What Bio Based Replaces in a TPU
TPU is made from a polyol, a diisocyanate and a chain extender. Bio based grades substitute part of the polyol with a plant-derived equivalent, typically from vegetable oils, corn or sugar cane feedstock.
The diisocyanate is usually still petrochemical, which caps the achievable bio content. That is why a "bio based" film may carry 20 to 60 percent renewable carbon rather than the 100 percent a buyer might imagine.
The soft segment is where the substitution happens, so the effect on properties is concentrated there. Hardness, elasticity and low-temperature behaviour all depend on that segment, which is why bio content changes the feel of the film.
Grades with higher bio content usually need more formulation work to match the mechanical profile of the petrochemical equivalent. The substitution is not a one-for-one swap at the molecular level.
Two Ways Bio Content Is Counted
Bio content can be physically segregated or attributed through mass balance, and the two are not equivalent when a buyer checks the claim.
Physically segregated material keeps renewable feedstock in a dedicated chain from the plant to the pellet. The bio content in the pellet is the bio content that was put in, and the claim is straightforward to verify.
Mass balance allows renewable and conventional feedstock to be mixed in a system and the renewable share to be allocated to a batch by bookkeeping. The environmental benefit is real at the system level, but the specific pellet is not necessarily made from plant carbon.
Both approaches can be legitimate, and both should be named in the documentation. A certificate that states a percentage without stating the method leaves the buyer unable to compare one supplier against another.
How the Properties Shift
The most consistent change is a small drop in tensile strength and tear resistance at equal hardness. The bio-based soft segment is slightly less regular, which reduces the efficiency of strain-induced crystallisation.
Hydrolysis resistance can move in either direction depending on the feedstock and the stabiliser package. A bio-based polyester polyol may carry more residual moisture or a different acid value, so the hydrolysis behaviour has to be tested rather than assumed.
Colour is the change buyers notice first. Bio-based polyols often carry a slight yellow or amber tone that persists into the film, which is acceptable in opaque or dark products and a problem in clear or white ones.
Heat resistance and compression set are usually close to the petrochemical equivalent at moderate bio content, but the gap widens at high substitution levels. Above roughly half renewable carbon, the formulation has to be adjusted to hold the same service temperature.
Comparing a Bio Based Grade With a Standard One
| Property | Bio based TPU | Standard TPU |
|---|---|---|
| Renewable carbon content | Typically 20 to 60 percent | Zero by definition |
| Tensile strength | Slightly lower at equal hardness | Reference level |
| Colour | Warmer tone, harder to keep white | Neutral, easier to match |
| Biodegradation | Not implied by the bio content | Not biodegradable in normal service |
| Batch consistency | More variation between lots | Tighter, established supply |
| Cost | Higher, and volatile with feedstock | Lower and more stable |
The biodegradation row is the one to read twice. Bio based and biodegradable are separate attributes, and a bio based TPU part will persist in the environment exactly as a conventional one does.
Certification and What a Claim Needs
A bio content claim needs a method, a percentage and a boundary. Without all three, two suppliers can quote the same number and mean different things.
- The test method used to determine the renewable carbon share
- Whether the material is physically segregated or mass balance allocated
- Whether the percentage refers to the polymer, the film or the finished article
- The certification body and the certificate number, so the claim can be checked
- The date of assessment, since feedstock and formulation change over time
Be careful with the word sustainable. It is not a defined technical term for a material and it cannot be verified in the way a percentage can, so it belongs in marketing copy rather than in a specification.
What Bio Content Does to Processing
Bio-based polyols are not identical to petrochemical ones, and the difference shows up on the line. Viscosity, hydroxyl value and residual acidity can all sit in a slightly different range, which changes how the polymer behaves in the melt.
Drying is more critical rather than less. A bio-based grade can carry a higher initial moisture level, and residual water in a hygroscopic polymer produces bubbles and a measurable loss of strength during extrusion.
Melt temperature windows can shift by a few degrees, which matters on a line that is already running close to the limit. The processing window should be re-established for the bio grade rather than carried over from the standard one.
Scrap handling also needs attention. Regrind from a bio-based grade should be kept separate from conventional material if the renewable content claim has to be preserved, otherwise the accounting behind the claim breaks down.
Shelf life is worth rechecking as well. A bio-based polyol can be more sensitive to moisture during storage, so the drying routine and the storage conditions that were adequate for the standard grade may need to be tightened.
Where Bio Based TPU Is Worth Specifying
Bio based grades make sense where a brand has a renewable content target, where the product is opaque or dark so colour shift is invisible, and where the application does not sit at the edge of the material's temperature range.
They are a poor fit for optical films, for very tight colour matching and for applications where batch-to-batch consistency matters more than the sustainability story. The variation is manageable but it is real.
A common approach is a mid-range bio content that captures most of the marketing value without moving the mechanical profile far enough to require requalification. That is a commercial decision as much as a technical one.
A Specification Sequence
- Confirm whether the target is renewable content, biodegradation, or both
- Decide the bio content percentage and the counting method before requesting samples
- Test tensile, tear and hydrolysis on the bio grade against the incumbent
- Check colour on the actual product, not on a plaque
- Ask for the certificate, the method and the boundary in writing
The available film grades are listed on the TPU film product range, and a bio based option should be requested as a specific grade rather than as a general substitution.
Zhejiang Huanlong New Material Science Technology Co.,Ltd produces blown, extruded and foamed film on 44 lines across three manufacturing bases, with two R&D centres and more than 30 engineers. Huanlong holds GRS, OEKO-TEX® 100, Bluesign® and ISO 9001:2015 certification, and can advise on which film ranges are available with renewable content.
The short version: bio based means plant-derived carbon, not biodegradability. Expect a small strength loss, a warmer colour and more batch variation, and insist on a method plus a percentage in the certificate.
Bio content is a feedstock claim, not an end-of-life claim.
Frequently Asked Questions About Bio Based TPU Film
Is bio based TPU biodegradable?
No. Bio based refers to the origin of the carbon, and the polymer backbone is the same durable structure. Biodegradation has to be designed and certified separately.
What percentage of bio content is realistic?
Most commercial grades sit between 20 and 60 percent renewable carbon, because the diisocyanate component is usually petrochemical. Higher figures exist but need specific formulation work.
Why is bio based film more yellow?
Plant-derived polyols carry natural colour bodies that survive processing. It is cosmetic in most applications but disqualifying in clear or white products unless the grade is specifically refined.
Does mass balance mean the film is not really bio based?
The renewable feedstock was genuinely used in the system, but it may not be in that specific pellet. It is a legitimate accounting method, and it should be declared as such rather than presented as physical segregation.
Can bio based TPU be recycled?
It is thermoplastic, so it can be reprocessed in the same way as conventional TPU. It should not be mixed into a stream where the bio content claim has to be preserved without accounting for it.
Send the renewable content target, the colour requirement and the mechanical profile, and a grade can be proposed against it. Huanlong can advise which bio based TPU film options are available and how they compare with the standard range.
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