PVC is the one commodity polymer where you cannot treat colour as an afterthought, because PVC is chemically fragile at its own processing temperature. Polyethylene tolerates a wide window. PVC sits close to its decomposition point whenever it is being processed, and anything you add either helps it survive that or does not.
This article covers how pipe and conduit are coloured in practice, why the answer differs between PVC and polyolefins, and what the colour system has to do besides look right.
Start with why PVC is different
Unplasticised PVC begins to dehydrochlorinate – split off hydrogen chloride – at temperatures very close to the ones needed to process it. The released HCl catalyses further decomposition, so the reaction accelerates once it begins. The visible progression is familiar to anyone who has run a PVC line: yellow, then amber, then brown, then black, and finally a scorched deposit on the screw.
Everything in a PVC formulation is arranged around holding that reaction back. Heat stabilisers – calcium-zinc systems now dominant in India for potable and conduit applications – scavenge HCl. Lubricants control friction and therefore shear heat. Processing aids control fusion. It is a compound in the true sense, not a resin with something added.
Two consequences follow for colour:
PVC is usually dry-blended, not masterbatch-coloured. Because PVC is already being compounded from a recipe of resin, stabiliser, lubricant, filler and processing aid in a high-speed mixer, pigment is normally added at that stage as a dry powder or as a pigment preparation. Adding a separate carrier-based masterbatch means adding a polymer that is not part of the qualified recipe.
Pigment choice is constrained by chemistry, not only by shade. A pigment that is fine in polyethylene may be unusable in PVC because it interacts with the stabiliser system, or because it is not stable at PVC fusion temperature, or because it contains metals the application prohibits.
Being straightforward about this matters. If a supplier offers you a generic polyolefin-carrier masterbatch for a PVC pipe line without asking about your stabiliser package, they have not thought about your process.
Where masterbatch does belong
There are real cases for a concentrate rather than dry pigment.
Non-PVC conduit and pipe. A great deal of Indian electrical conduit and duct is now HDPE or PP rather than PVC – flexible corrugated conduit, HDPE telecom duct, and PLB duct in particular. These are conventional polyolefins and are coloured with ordinary colour masterbatch and black masterbatch exactly as any other polyolefin extrusion would be.
Stripes and identification bands on both PVC and polyolefin pipe, which are small co-extruded beads where a concentrate is the practical delivery form.
Small-run and frequent colour changes, where handling dry pigment for every shade is impractical and dusty.
Dosing accuracy. Dry pigment weighed by hand in a mixer room is only as consistent as the person weighing it. A pelletised concentrate metered gravimetrically is repeatable.
For polyolefin conduit and duct, this is straightforward work and we treat it like any other pipe extrusion job – see masterbatch for HDPE pipe extrusion.
Conduit colour and what it signals
Colour on electrical conduit and duct is functional. It identifies the service so that whoever excavates or opens a wall in ten years knows what they have found.
Indian practice follows the relevant product standards and utility conventions, and the exact scheme varies between electricity boards, telecom operators and specifying authorities. Rather than assume, confirm the colour requirement against the specification you are supplying to – a colour that is right for one utility can be wrong for another.
What is universal is the requirement underneath: the colour must remain identifiable for the life of the installation. That turns a cosmetic property into a durability one.
What conduit colour has to survive
| Condition | What it does | What the formulation needs |
| Direct sunlight before burial | Fades and chalks the surface | UV stabiliser package, or carbon black |
| Long-term burial | Little UV, but chemical contact with soil and water | Migration-resistant, non-extractable pigments |
| Surface conduit indoors | Ambient light, cleaning agents | Chemical resistance, no plasticiser interaction |
| Processing heat | Degrades unstable pigments | Pigments stable at PVC fusion temperature |
| Cable pulling | Abrasion at the bore | Colour throughout the wall, not a surface coating |
The first row catches people out most often. Conduit and duct spend months in the sun on site before they are installed, stacked in open yards through an Indian summer. A formulation designed only for the buried service life is not designed for the storage that precedes it. Orange and yellow duct, common for telecom, is particularly prone to visible fade because those pigment classes are among the harder ones to keep lightfast at reasonable cost.
Where UV performance is required, the mechanisms are the same as anywhere else – see HALS vs UV absorbers.
Filler, and why colour targets drift
PVC pipe and conduit almost always contain calcium carbonate filler, at levels that can be substantial in non-pressure applications. Filler is not colour-neutral – it is a white mineral with its own opacity and its own effect on shade.
When the filler loading changes, the colour changes. A plant that adjusts filler percentage for cost reasons and then complains that the pigment supplier has changed something is a recurring story. If your filler loading moves between lots, your colour will move with it and no amount of pigment consistency will fix that.
The same applies to the stabiliser system. Lead-based stabilisers, historically common and now displaced in most applications, have a different base colour from calcium-zinc systems. A recipe conversion changes the substrate you are matching against.
This is a specific case of a general problem covered in why colour drifts between batches: before blaming the colourant, check whether the thing being coloured has changed.
Heavy metals and compliance
Two constraints apply commonly:
Potable water. Pipe and fittings in contact with drinking water must meet the applicable standard for materials in contact with water. That restricts both the stabiliser system and the pigment set.
RoHS and general heavy metal limits. Electrical products supplied into regulated markets carry restrictions on lead, cadmium, mercury and hexavalent chromium. Several traditional pigments – lead chromate yellows and oranges in particular – are excluded on exactly this basis. If your conduit is going into an export assembly, the pigment declaration matters as much as the polymer.
We can provide RoHS and REACH declarations where the application requires them. Our manufacturing is under ISO 9001:2015.
Practical checklist before you order
– Polymer: PVC compound, HDPE, or PP – and if PVC, the stabiliser system – Filler loading, and whether it is stable between lots – Process: extrusion profile, temperatures, line speed – Colour reference and the tolerance you will accept – Service environment: buried, surface, indoor, and how long in open storage before installation – UV life required, in exposure terms not just months – Regulatory: potable water contact, RoHS, any customer-specific restricted substance list – Stripe or band requirements, with the carrier matched to the base
Talk to us
Life Color Pigments & Masterbatches supplies colour and black masterbatch for polyolefin conduit, duct and pipe, and pigment systems for coloured extrusion generally. Where the substrate is PVC, we will want to know your stabiliser and filler package before quoting, because a pigment recommendation made without it is a guess.
Tell us the polymer, the standard you supply to and the service environment and we will formulate against them.
Related: electrical applications, building and construction, water management, masterbatch for wire and cable.
FAQs
Can you use normal masterbatch in PVC? Usually not without thought. PVC is compounded from a recipe of resin, heat stabiliser, lubricant, filler and processing aid, and pigment is normally added as dry powder at that stage. A polyolefin-carrier masterbatch introduces a polymer that is not part of the qualified recipe, and pigments must also be compatible with the stabiliser system.
Why does PVC turn yellow or brown during processing? Because PVC dehydrochlorinates at temperatures very close to its processing range, releasing hydrogen chloride which then catalyses further decomposition. The colour progression from yellow through amber to brown and black is the visible record of that reaction. Heat stabilisers exist to hold it back.
Is electrical conduit made from PVC or HDPE? Both. Rigid conduit is commonly PVC, while flexible corrugated conduit, telecom duct and PLB duct are frequently HDPE or PP. The polyolefin types are coloured with conventional masterbatch; PVC is generally dry-blended.
Why does coloured conduit fade before it is even installed? Because it sits in open yards in direct sunlight for weeks or months before installation. A formulation designed for the buried service life is not designed for that exposure. Orange and yellow duct fades most visibly, since those pigment classes are the hardest to keep lightfast cheaply.
Does calcium carbonate filler change the colour of PVC pipe? Yes. Calcium carbonate is a white mineral with its own opacity, so changing the filler loading changes the shade even with identical pigment. If filler percentage varies between production lots, colour will vary with it.
What colour should electrical conduit be in India? It depends on the specification you are supplying against – schemes differ between electricity boards, telecom operators and specifying authorities. Confirm the requirement against the applicable standard for the project rather than assuming a universal code.
Are lead-based pigments allowed in conduit? Not where RoHS or an equivalent restricted substance requirement applies, and lead chromate yellows and oranges are excluded on that basis. Potable water applications carry their own restrictions on both pigment and stabiliser systems.