Compostable and Biodegradable Plastics: What CPCB Requires

“Biodegradable” and “compostable” are not the same claim, and only one of them is defined tightly enough to be enforceable. Nearly everything degrades eventually; the question a standard answers is how completely, under what conditions, in what time, and leaving what behind.

Getting this wrong has direct consequences in India, where single-use plastic restrictions turn on exactly this distinction.

The definitions that matter

Biodegradable means the material can be broken down by microorganisms. On its own the word is close to meaningless as a specification – it carries no requirement on conditions, timeframe or completeness. A conventional polyolefin will biodegrade given long enough, which is why the unqualified claim is treated with suspicion by regulators worldwide.

Compostable is a defined, testable claim. To be certified compostable a material must, under specified composting conditions:

1. Disintegrate – break into fragments below a defined size within a set period 2. Biodegrade – convert to carbon dioxide, water and biomass to a defined percentage within a set period 3. Show no ecotoxicity – the resulting compost must support plant growth and not exceed heavy metal limits 4. Contain no excessive regulated substances

Industrially compostable requires the elevated temperature, controlled humidity and managed conditions of an industrial composting facility. Home compostable is a stricter claim requiring degradation at ambient temperature, and far fewer materials achieve it.

The distinction matters practically: an industrially compostable bag in a landfill or in a home compost heap does not compost. It requires a facility that must actually exist and actually receive the material. This is the central weakness of compostable packaging in markets without composting infrastructure, and it is a fair question to be able to answer.

The Indian framework

Under the Plastic Waste Management Rules and the single-use plastic restrictions, compostable plastic products require certification from CPCB, and only certified material may be sold as compostable. Certification is assessed against the applicable Indian Standard for biodegradable and compostable plastics, which aligns with the international test framework.

The internationally recognised standards behind this are ISO 17088, EN 13432 for packaging and ASTM D6400.

Compostable plastic packaging is Category IV under the EPR framework, treated separately from rigid, flexible and multilayer categories – see EPR for plastic packaging in India.

Two things follow that catch manufacturers out:

The certificate belongs to the finished product, not the resin. Certification applies to the article as made, in its actual formulation and thickness. Buying certified resin does not make your bag certified.

Uncertified compostable claims are an enforcement risk. Making the claim without the certificate is a compliance exposure, not a marketing choice.

The materials

Material	Source	Notes
PLA (polylactic acid)	Corn starch, sugarcane	The most common; industrially compostable, not home compostable, low heat resistance
PBAT	Petrochemical	Flexible, compostable, usually blended with PLA or starch
PHA / PHB	Bacterial fermentation	Home compostable and marine biodegradable in some grades; expensive
Starch blends	Corn, potato, tapioca	Low cost, moisture sensitive, usually blended
PBS	Part bio-based	Better heat resistance than PLA

Note that “bio-based” and “compostable” are independent properties. Bio-PE made from sugarcane ethanol is chemically identical to conventional polyethylene – fully recyclable and not compostable at all. Conversely PBAT is petrochemical in origin and is compostable. Feedstock and end-of-life behaviour are separate questions, and conflating them is one of the most common errors in sustainability claims.

Why the colourant has to be certified too

This is where masterbatch enters, and it is not a formality.

Compostability certification assesses the whole material, including every additive and colourant. A conventional pigment package will generally fail, for three reasons:

Heavy metal limits. The standards set limits on regulated elements in the finished compost. Several conventional pigments exceed them.

Ecotoxicity. The resulting compost must support plant growth. Pigments and additives that inhibit germination or growth fail this test regardless of their heavy metal content.

Biodegradation of the colourant itself. Non-degrading residues remaining in the compost are a problem in their own right.

So a certified compostable film coloured with an ordinary masterbatch is no longer certified compostable. The polymer did not change; the article did, and the article is what carries the certificate.

Colourants for compostable substrates must be selected from pigment sets assessed against these requirements, on carriers that are themselves compostable. If you are colouring a certified compostable substrate, say so on the enquiry – it is not a variant of a normal order, and we will need to know before quoting.

Processing differences

Compostable polymers do not behave like polyolefins.

PLA is hygroscopic and hydrolyses at melt temperature, exactly as PET does. It must be dried thoroughly, and so must anything else entering the melt – including the colour concentrate. The consequence is the same permanent molecular weight loss described in PET preform and bottle masterbatch.

Processing windows are narrower. Most compostable polymers degrade at temperatures not far above their processing range.

Heat resistance is low. PLA softens around 55 to 60°C, which rules out hot-fill, dishwashers and many Indian ambient storage conditions.

Shelf life is finite. These materials are designed to degrade, and degradation does not wait for disposal. Warm, humid storage – which is to say, most of India for much of the year – shortens usable life, and this needs to be built into stock planning rather than discovered.

Barrier properties differ, generally worse for moisture, which affects food shelf life.

Being honest about the trade-offs

Compostable plastics have real applications and real limitations, and a supplier who names both is more useful than one who does not.

Where they genuinely work: organic waste collection bags, where the bag and its contents go to the same composting facility. Food service items at controlled venues with their own composting. Agricultural mulch film certified for soil biodegradation, which avoids the substantial problem of retrieving conventional mulch film from a field – see UV masterbatch for mulch and agricultural film.

Where they do not: any application where the item will predictably end up in landfill or in the conventional recycling stream. In landfill, compostable plastic does not compost and may generate methane. In the recycling stream it is a contaminant – PLA in a PET recycling line is a genuine problem, since the two are difficult to separate and PLA degrades PET during reprocessing.

Compostable and recyclable are competing strategies, not complementary ones. Deciding between them means deciding which end-of-life infrastructure your product will actually reach – which is a question about waste management in your market, not about the material.

What to establish before committing

– Is the claim industrially compostable or home compostable, and does the required infrastructure exist where the product is sold? – Is the finished article CPCB certified, not just the resin? – Are the colourant and every additive included in that certification? – What is the heat resistance required, and does the material meet it? – What is the shelf life under Indian storage conditions? – Which EPR category does the product fall in, and what are its obligations? – Would recyclable mono-material serve the same purpose better?

That last question deserves genuine consideration rather than a reflexive answer. For a great many packaging applications, a well-designed recyclable mono-material structure delivers more environmental benefit than a compostable one that reaches no composting facility.

Talk to us

Life Color Pigments & Masterbatches manufactures under ISO 9001:2015 and supplies colour, white and additive masterbatches across conventional and recycled polymer systems.

If you are colouring a certified compostable substrate, tell us the base polymer, the certification you hold and the standard it was assessed against before ordering – the pigment and carrier requirements are different, and a conventional concentrate will invalidate the certificate you paid for.

Related: sustainability, recycling masterbatches, agriculture, packaging.

FAQs

What is the difference between biodegradable and compostable? Biodegradable only means microorganisms can break the material down, with no requirement on conditions, timeframe or completeness – which makes it close to meaningless as a specification. Compostable is a defined, testable claim covering disintegration, percentage biodegradation, ecotoxicity and regulated substances.

Do compostable plastics need CPCB certification in India? Yes. Under the plastic waste rules and single-use plastic restrictions, compostable plastic products require CPCB certification, and only certified material may be sold as compostable. The certificate applies to the finished product, not to the resin it was made from.

Which standards cover compostable plastics? Internationally, ISO 17088, EN 13432 for packaging and ASTM D6400, with the corresponding Indian Standard used for CPCB certification. All assess disintegration, biodegradation percentage, ecotoxicity and heavy metal content.

Does the colourant need to be certified for compostable plastic? Yes. Certification assesses the whole material including every additive and pigment, against heavy metal limits, ecotoxicity in the resulting compost, and residue. A certified compostable film coloured with a conventional masterbatch is no longer certified.

Is bio-based plastic the same as compostable? No, they are independent properties. Bio-PE from sugarcane is chemically identical to conventional polyethylene – recyclable and not compostable. PBAT is petrochemical in origin and is compostable. Feedstock and end-of-life behaviour are separate questions.

What happens to compostable plastic in a landfill? It does not compost. Industrial composting requires elevated temperature and controlled conditions that a landfill does not provide, and anaerobic conditions there can generate methane. Compostable packaging only delivers its benefit if it actually reaches a composting facility.

Can compostable plastic go in the recycling stream? No, it is a contaminant. PLA in a PET recycling line is a particular problem because the two are difficult to separate and PLA degrades PET during reprocessing. Compostable and recyclable are competing strategies rather than complementary ones.

Does PLA need drying before processing? Yes. PLA is hygroscopic and hydrolyses at melt temperature, causing permanent molecular weight loss, so it must be thoroughly dried – and so must any colour concentrate entering the melt. Its processing window is also narrow and its heat resistance low, softening around 55 to 60 degrees.