PET punishes a masterbatch choice that polypropylene would forgive. The same colourant, carried in the wrong polymer, gives you haze in a bottle that had to be crystal clear, an intrinsic viscosity drop that ruins blow performance, or an acetaldehyde level that a water bottler will reject.
If you mould preforms, blow bottles or extrude sheet, this is what to check before the first order.
Carrier choice is the whole decision
In polyolefins you have latitude. A PE-carrier masterbatch in a PP part is usually acceptable. In PET it is not.
A polyolefin carrier in PET is immiscible. It will not disperse into the matrix, and in a clear bottle you see it — haze, and in bad cases visible streaking. For any clear or lightly tinted PET application, the carrier has to be compatible with PET.
What to ask: what is the carrier, and is it suitable for a clear PET application? A supplier offering their general-purpose colour masterbatch for PET preform work either has a PET-specific grade they have not mentioned, or has not understood the application.
Moisture, and why it matters more here
PET hydrolyses at processing temperature in the presence of moisture. The chain breaks, intrinsic viscosity falls, and the material loses the melt strength that stretch blow moulding depends on.
Preform moulders dry PET resin carefully — typically to very low moisture before processing. Then some of them add a masterbatch straight from an unsealed bag.
The masterbatch has to be dried to the same discipline as the resin, and its carrier has to tolerate that drying. This is a frequent and entirely avoidable cause of IV loss that gets blamed on the resin supplier.
What to ask: what is the recommended drying regime for this masterbatch, and is the packaging moisture-barrier?
IV drop, and how to see it coming
Intrinsic viscosity is the practical measure of molecular weight in PET, and it governs whether a preform blows properly.
Masterbatch contributes to IV drop through three routes:
- Moisture carried in, as above
- A carrier that degrades at PET processing temperature, generating acidic by-products
- Additives that catalyse chain scission at temperature
What to ask: what IV drop should I expect at my let-down ratio and my processing profile? A supplier who has run this will have a view. One who has not will say it is negligible.
Acetaldehyde, and the water-bottle problem
PET generates acetaldehyde as a thermal degradation product. In water bottles it is a taste issue at very low concentrations, which is why water bottlers specify AA limits that other PET users never think about.
Anything that increases thermal stress — a masterbatch needing a higher melt temperature, a carrier that degrades, poor dispersion forcing more shear — increases AA.
If you mould for a water bottler, AA is a specification you have to meet, and the colourant is part of the system that determines it.
What to ask: has this grade been used in water-bottle applications, and what is its contribution to AA?
Clarity and haze
For clear and tinted bottles, haze is the measure that matters, and it comes from carrier incompatibility, undispersed pigment, and in some cases from the pigment choice itself.
Organic pigments at low loading generally give cleaner transparency than inorganics, which are opaque by nature. If you want a transparent tint, the pigment set is constrained before you start.
What to ask: what haze contribution should I expect at my let-down ratio and my wall thickness?
UV blocking for bottles
A common and genuinely commercial requirement. Products sensitive to light — edible oils, some dairy, certain pharmaceuticals, beer — need UV protection built into the bottle.
This is a different product from a colourant. It can be done with UV absorbers in a clear bottle, or with pigments that block the relevant wavelengths in an opaque one. The specification should state which wavelengths and what transmission limit, because “UV protection” without numbers cannot be verified.
What to ask: what transmission does this achieve at my wall thickness, across what wavelength range?
Compliance, which is nearly always food contact
Most PET masterbatch ends up touching food or drink, so the documentation burden is higher than for most grades.
| Application | Ask for |
| Food and beverage contact | FSSAI, plus the applicable IS specification, declared for your grade |
| Water bottles | The above, plus an AA position |
| Pharmaceutical packaging | The relevant pharmacopoeial requirement for the pack |
| EU export | REACH, plus the EU food-contact framework |
A company ISO 9001 certificate does not answer any of these. Ask for a declaration naming your grade. We cover the Indian framework in food contact plastics: FSSAI and IS 10146.
Recycled PET
rPET brings its own variables — colour variability in the input, residual contamination, and IV that is already lower than virgin.
Colouring rPET usually means working to a wider tolerance, or accepting that a light shade is not achievable from a given feedstock. A supplier who tells you a pale tint is not realistic on your rPET stream is being useful rather than unhelpful. See masterbatch for recycled and PCR plastic.
What to ask a PET masterbatch supplier
- What carrier, and is it suitable for clear PET?
- What drying regime does the masterbatch need, and is the packaging a moisture barrier?
- What IV drop at my let-down ratio and processing profile?
- What is the acetaldehyde contribution? (essential for water)
- What haze at my wall thickness?
- For UV grades — what transmission, across what wavelengths, at what thickness?
- Can you give me a grade-level food-contact declaration?
Talk to us
We manufacture PET masterbatch on our own lines at Vasai under ISO 9001:2015, formulated for the moisture sensitivity and narrow processing window that PET actually has rather than adapted from a polyolefin grade.
Tell us whether you are moulding preforms, blowing bottles or extruding sheet, your resin grade and IV, your wall thickness, your shade or UV requirement and your end market — and we will propose a grade and a trial. Related: PET masterbatches, colour masterbatches, additive masterbatches, packaging, pharma.
Frequently asked questions
Can I use ordinary colour masterbatch in PET?
Not for clear or lightly tinted applications. A polyolefin carrier is immiscible in PET and shows up as haze and sometimes visible streaking. PET applications need a carrier compatible with PET.
Does masterbatch need to be dried before use in PET?
Yes, to the same discipline as the PET resin itself. PET hydrolyses at processing temperature in the presence of moisture, and adding undried masterbatch to carefully dried resin is a common and avoidable cause of intrinsic viscosity loss.
What causes IV drop when adding masterbatch to PET?
Moisture carried in with the masterbatch, a carrier that degrades at PET processing temperature and generates acidic by-products, or additives that catalyse chain scission. All three are formulation and handling questions rather than inevitable.
Why does acetaldehyde matter in PET bottles?
Acetaldehyde is a thermal degradation product of PET and affects taste at very low concentrations, which makes it a specification for water bottlers. Anything increasing thermal stress – higher melt temperature, a degrading carrier, poor dispersion – increases it.
What causes haze in coloured PET bottles?
Carrier incompatibility is the usual cause, followed by undispersed pigment. Pigment choice also matters, since inorganic pigments are opaque by nature and will not give a transparent tint.
How do I specify UV protection for a PET bottle?
State the wavelength range and the transmission limit required at your wall thickness. “UV protection” without numbers cannot be verified, and the right approach differs between a clear bottle, which needs UV absorbers, and an opaque one, which can use blocking pigments.
Is PET masterbatch suitable for food contact?
It depends on the grade. Ask for a declaration naming your specific grade against FSSAI and the applicable IS specification, and for export markets against REACH and the relevant food-contact framework. A company ISO certificate does not answer this.
Can rPET be coloured to the same tolerance as virgin PET?
Usually not. Recycled feedstock varies in colour, carries residual contamination and already has lower IV, so colour tolerances are typically wider and pale shades may not be achievable from a given stream.
Buying masterbatch for this application?
We manufacture in Vasai and supply converters across India. Tell us the polymer and the process, and we will come back with a grade and a price.