A tarpaulin fails long before it looks failed. The sheet still looks serviceable, the colour is only slightly faded, and then it tears along a fold under a load it carried easily last season. That is photo-oxidative degradation reaching the point where the tape has lost most of its tensile strength while retaining most of its appearance.

Woven HDPE tarpaulin and shade net are among the most demanding UV applications in Indian plastics: thin monoaxially oriented tape, permanently outdoors, under some of the highest solar radiation in the world, and sold on a service-life promise.

How the product is built

Both products start the same way. HDPE, or a HDPE-LLDPE blend, is extruded as a flat film, slit into narrow tapes, and stretched at high draw ratio to orient the molecules along the tape axis. That orientation is what gives the tape its tensile strength.

The tapes are then woven on circular or flat looms. Tarpaulin is woven into a dense fabric and usually laminated on one or both faces with an LDPE or LLDPE coating for waterproofing. Shade net is knitted or woven to a deliberately open structure that passes a controlled fraction of the light.

Two features of this construction drive the UV problem:

The tape is thin. Typical tape is tens of microns. There is almost no path length, which – as covered in HALS vs UV absorbers – means a UV absorber contributes very little and HALS must do the work.

The tape is oriented and under tension. Oriented polymer under stress degrades faster than the same polymer unstressed, and once a tape starts to fail it fails along its length. The fabric loses strength as a whole because every tape in it is degrading together.

What actually degrades

Sunlight breaks bonds, generating free radicals that propagate an oxidation chain reaction through the polymer. In a stretched tape the consequences arrive in a specific order:

1. Surface chalking and gloss loss – cosmetic, early 2. Fading – the pigment, not the polymer, in many cases 3. Loss of elongation at break – the tape becomes brittle before it becomes weak 4. Loss of tensile strength – the failure that matters 5. Tearing under normal service load

Elongation goes first, and this is what makes tarpaulin failure feel sudden. A tarpaulin that has lost elongation cannot absorb a shock load – a gust, a snag, a pull over a corner – and tears where it would previously have stretched. Nothing visible warned anybody.

The standard measure of end of life is therefore retained tensile strength after defined exposure, commonly 50% retention. A supplier quoting a life in months without stating retained strength and exposure is quoting nothing.

Specifying UV life honestly

The industry convention for exposed film and fabric is kilolangleys (kLy) – cumulative solar radiation the product must survive, rather than calendar months.

This is not jargon for its own sake. India’s solar radiation varies widely by region, and a tarpaulin in coastal Kerala and one in western Rajasthan accumulate very different exposure in the same twelve months. A product rated in months is making a promise that depends entirely on where the buyer lives. A product rated in kLy makes a promise that can be converted to months once the site is known.

Ask for the kLy rating, the retained tensile criterion and the test basis. Together those three make a specification. Any one alone does not.

What goes into the tape

HALS is the primary protection, for the thickness reason above. Molecular weight matters: a thin tape has a very high surface-to-volume ratio, so a low molecular weight HALS is lost to volatilisation and rain extraction faster than the product’s intended life. High molecular weight or polymeric HALS stay in the tape.

UV absorbers contribute modestly and are usually present as a supplement rather than the main defence.

Antioxidants protect during processing. The tape passes through extrusion and high-temperature orientation, and thermal-oxidative damage taken there is damage the UV package then has to compensate for.

Pigment matters more than people expect:

– Carbon black is an excellent UV screen. A black tarpaulin is inherently better protected than a coloured one at the same stabiliser loading – one reason black and dark grey dominate heavy-duty tarpaulin. – Titanium dioxide must be a surface-treated rutile grade. Anatase TiO2 is photocatalytic and will accelerate degradation of the polymer around it. This is a genuine failure mode in white and light-coloured products, covered in titanium dioxide in plastics. – Organic pigments vary enormously in lightfastness. Blue and green tarpaulin – the commodity Indian shades – hold up reasonably in good pigment classes and fade quickly in cheap ones. This is where cost-cutting shows first and most visibly.

Our additive masterbatches carry the stabiliser package and our colour and black masterbatches carry the pigment; for tape they are commonly combined into a single concentrate so the converter runs one product.

Shade net: percentage is an optical specification

Shade net is sold by shade percentage – 35%, 50%, 75%, 90% – which is the fraction of incident light the net blocks.

That percentage is delivered by two things together: the openness of the knit or weave, and the opacity and colour of the tape itself. A net can be made to the same geometry in two different tape formulations and deliver different shade values.

Colour is functional here, not decorative.

– Black blocks the most light per unit of material and is the most durable, since carbon black is protecting the tape. It also absorbs heat and re-radiates it, raising temperature under the net. – Green is conventional for horticulture and blocks less than black at the same geometry. – White and silver reflect rather than absorb, keeping the space under the net cooler – valuable in hot regions, and more demanding on the UV package because there is no carbon black protection. – Aluminised and reflective nets are used where thermal management is the primary purpose.

The trade-off is direct: the colours that keep the crop coolest are the colours that protect the net least. A white or silver net needs a substantially stronger stabiliser package than a black one to reach the same service life, and pricing that ignores this produces a product that fails early.

The agrochemical problem

This is the failure cause most often missed in Indian agriculture.

Shade nets and greenhouse structures are sprayed. Sulphur and halogen-based pesticides attack conventional HALS, deactivating the stabiliser chemistry that the entire service life depends on. A net formulated and tested without chemical exposure can lose a large fraction of its predicted life in a sprayed environment.

Films and nets for agricultural use should specify pesticide-resistant HALS chemistry. If a supplier has never been asked the question, the product probably does not have it. We cover the same issue for mulch and agricultural film.

Where else the same tape technology goes

The UV requirements above apply across the woven HDPE family, with differences of degree:

– PP woven sacks and FIBC – polypropylene, more UV-sensitive than HDPE, and with a safety obligation where FIBC carry load – Ground cover and weed mat – permanently exposed, usually black – Silage and bale wrap – short life, high stretch, different priorities – Geotextiles – buried or covered, so UV exposure is limited to the installation window

Buying checklist

– Polymer and blend – HDPE, or HDPE-LLDPE, and tape denier – Required UV life in kLy, plus the region of use – Retained tensile criterion at end of life – Colour, and whether it is functional (shade percentage, heat management) or cosmetic – Chemical exposure – which agrochemicals, how often – Lamination – whether a coating layer needs its own stabilisation – Whether the product is sold with a written life guarantee, since that determines how much margin the formulation needs

Talk to us

Life Color Pigments & Masterbatches supplies UV and colour concentrates for tape extrusion, tarpaulin and shade net, manufactured under ISO 9001:2015.

Tell us your tape construction, the region it will be used in, the shade percentage and what will be sprayed near it, and we will formulate to a kLy target rather than to a guess.

Related: agriculture, packaging, carbon black and UV protection.

FAQs

Why does tarpaulin tear even when it still looks fine? Because elongation at break is lost before tensile strength and long before appearance. A degraded tarpaulin cannot absorb a shock load, so it tears at a snag or a gust where it would previously have stretched. Appearance is a poor guide to remaining strength.

How is UV life of tarpaulin measured? By retained tensile strength after a defined exposure, commonly 50 percent retention as end of life, with exposure expressed in kilolangleys of cumulative solar radiation. Quoting a life in months alone is meaningless without the region and the retained strength criterion.

What is a kilolangley? A unit of cumulative solar radiation. Rating a product in kLy rather than months lets you convert to a calendar life once the site is known, which matters in India because annual radiation varies widely between regions.

Why is black tarpaulin more durable than coloured? Because carbon black is an excellent ultraviolet screen in its own right and protects the polymer in addition to the stabiliser package. A coloured tarpaulin has no such screen and depends entirely on its HALS and antioxidant system.

Does shade net colour affect performance? Yes, in two ways. Black blocks the most light and is the most durable but absorbs heat. White and silver reflect and keep the space beneath cooler but have no carbon black protection, so they need a stronger stabiliser package to reach the same life.

Do pesticides damage shade net and greenhouse film? Significantly. Sulphur and halogen-based agrochemicals deactivate conventional HALS, which is the primary UV protection in thin tape. Products for sprayed environments should use pesticide-resistant HALS chemistry, and this should be asked for explicitly.

Why do UV absorbers not work well in tape? Because absorption depends on path length and a woven tape is only tens of microns thick. Most incident ultraviolet passes straight through before it can be absorbed. HALS work by scavenging radicals and have no thickness dependence, which makes them the primary protection.

What determines the shade percentage of a shade net? The openness of the knit or weave together with the opacity and colour of the tape. Two nets of identical geometry can give different shade values if the tape formulations differ, so shade percentage should be verified on the finished product.