Agricultural film fails in the field for one of two reasons: it was under-stabilised for the radiation it had to survive, or the stabiliser was destroyed by something sprayed on the crop.
The second one causes more disputes than the first, and almost nobody writes about it.
Stop specifying film life in months
“Twelve-month mulch film” is not a specification. It is a hope.
A 25-micron black mulch film laid in Rajasthan in April and one laid in Kerala in July are not doing the same job. Solar radiation load in India varies enormously by region and season, and a film that comfortably survives a monsoon-season crop in the east will powder in a summer crop in the west.
The industry unit for this is the kilolangley (kLy) – a measure of accumulated solar radiation. One langley is one calorie per square centimetre.
A UV guarantee should be written as “retains X% of original tensile strength after Y kLy”, not as a number of months.
Roughly, high-radiation regions of western and north-western India accumulate meaningfully more kLy per year than the coastal south and east. So the same film gets a different working life in each. Ask your film buyer where the film is going and for how long, convert that to a kLy requirement, and specify against it. Then the guarantee means something and both sides know what was promised.
Practical consequence for you as a film maker: if you sell the same grade nationally against a “12 month” claim, you are absorbing the western-India failures in your margin.
HALS and UV absorbers do different jobs
There are two families of UV stabiliser and they are not interchangeable.
UV absorbers – benzophenones and benzotriazoles – work by absorbing UV energy and dissipating it as heat before it can break a polymer chain. They are consumed as they work. In a thin film there is very little material in the light path, so an absorber has limited opportunity to do its job. Absorbers are weak in thin gauges.
HALS – hindered amine light stabilisers – do not absorb UV. They scavenge the free radicals produced when degradation has already started, and they regenerate through a cycle rather than being consumed on first use. That regeneration is why HALS massively outperform absorbers in thin film, where they are the backbone of any serious agricultural package.
Most good agri-film packages use HALS as the primary, sometimes with an absorber as support, plus an antioxidant to handle processing.
If a supplier quotes you a “UV masterbatch” without telling you which chemistry, you cannot compare it against anything. Ask.
The pesticide problem – the real reason film fails early
This is the part that turns into a dispute at the end of the season.
Conventional HALS are basic compounds. They are chemically neutralised by acids. Several things a farmer routinely applies to a crop are, or become, acidic at the film surface:
- Sulphur-based fungicides – extremely common in Indian horticulture
- Chlorinated compounds, including chlorinated water and some fumigants
- Halogenated pesticides
- Soil fumigants used before laying mulch
Where these contact the film, they deactivate the HALS. The film then degrades at roughly the rate of unstabilised film, and it does so in patches – worst where spray drift concentrated, fine elsewhere. A blotchy failure pattern on a mulch film is a near-certain fingerprint of stabiliser antagonism rather than under-dosing.
The fix is chemistry, not more dosage. Adding more conventional HALS to a film that is being acid-attacked buys very little. NOR-HALS – the N-alkoxy type – are far less basic and hold up substantially better against agrochemical attack. They cost more. For a greenhouse film in a high-spray regime, they are usually the cheaper option once you count the replacement.
When you brief a masterbatch supplier for agricultural film, tell them the crop and the spray programme. A supplier who does not ask about pesticides is not formulating for your application.
Dosage: what actually drives the number
Typical UV masterbatch addition for agricultural film runs 2% to 7%, but the range is wide because four things move it:
| Factor | Effect on dosage |
| Required kLy lifetime | The dominant variable – doubling life more than doubles stabiliser |
| Film thickness | Thinner film needs more stabiliser per kg, because degradation is a surface-dominated process |
| Pesticide exposure | Drives chemistry choice, and dosage on top of it |
| Carbon black content | Black film is partly self-protecting – see below |
A dosage figure with no kLy target and no thickness attached is not a recommendation. It is a guess dressed as one.
Rather than converting these by hand each time you change gauge, use our let-down ratio calculator – it will take the active stabiliser percentage you need and give you the hopper setting for your grade.
Black, white-on-black, and silver mulch film
Mulch film is not one product, and the colour is doing agronomic work, not decoration.
Black mulch. The default. It blocks light to the soil surface, which is how it suppresses weeds. Carbon black is also, conveniently, an excellent UV screen – so a properly formulated black mulch film gets meaningful protection from the pigment itself and needs a lighter HALS package than a clear film of the same life. This only holds if the carbon black is a fine grade and properly dispersed; a coarse black looks equally black and screens far less.
White-on-black (co-extruded). White upper surface reflects light and heat back to the canopy and keeps the root zone cooler – used for summer crops where black would cook the soil. The black layer still does the weed suppression. Two layers, two different masterbatch requirements.
Silver-on-black. The silver surface reflects UV upward, which disorients aphids, thrips and whitefly and measurably reduces landing rates. This is an insect-management film. It carries a price premium and it is worth making properly.
Each of these is a different masterbatch specification. Selling all three off one UV grade is where quality complaints come from.
What to put on your enquiry
- Film type – mulch, greenhouse, tunnel, silage – and construction if co-extruded
- Thickness in microns
- Required life in kLy, plus the region
- The retained-property criterion – usually “≥50% of original tensile strength at end of life”
- Crop and spray programme, specifically any sulphur or chlorinated products
- Polymer and MFI
- Whether the film also needs anti-drip, thermic or diffusion properties
Then run an accelerated weathering trial before the season, not during it.
FAQs
How much UV masterbatch is needed for mulch film? Typically 2% to 7%, driven by the required kLy lifetime, film thickness and pesticide exposure. A recommendation without a kLy target and a thickness is not usable.
What does kLy mean in agricultural film? Kilolangley – accumulated solar radiation. It is the correct unit for a UV guarantee, because a film’s life depends on radiation received, not calendar months. The same film lasts different lengths of time in Rajasthan and Kerala.
Why did my mulch film fail before the guaranteed period? The most common cause is agrochemical antagonism. Sulphur-based fungicides and chlorinated compounds neutralise conventional HALS, causing patchy early failure. Uniform failure across the whole sheet points to under-dosing instead.
What is the difference between HALS and a UV absorber? An absorber soaks up UV energy and is consumed doing it. HALS scavenge the free radicals that degradation produces and regenerate through a cycle. In thin film there is too little material for an absorber to work well, so HALS carry the load.
Does black mulch film still need UV masterbatch? Usually yes, but less than a clear film of the same life, because well-dispersed fine-particle carbon black is itself an effective UV screen. Coarse carbon black looks just as black and protects far less.
What is NOR-HALS and when is it worth the money? NOR-HALS is a less basic, N-alkoxy form of hindered amine that resists acid and pesticide attack far better than conventional HALS. It is worth the premium wherever the film sees a heavy sulphur or chlorinated spray programme.