Introduction 

Mulch film is judged in the field, not in the warehouse. By the time a roll reaches the bed former, three things have already decided how the film will behave for the rest of the season:

how much carbon black is genuinely in the film, how evenly that carbon black is spread through a gauge that can be thinner than 15 μm,

and how well the polymer itself is protected once the film is down.

WMULCH-1 is 45% carbon black masterbatch built on polyethylene carrier and developed for blown agricultural film.

It is specified backwards from the film to reach a 2.0–3.0% carbon black level in the finished mulch at a practical let-down,

with the moisture level and dispersion quality that thin agricultural gauges cannot tolerate.

The sections below set out that engineering : how to calculate your own let-down, how to verify the delivery before it goes into the hopper,

what the black layer actually does agronomically, and where the honest limits of this grade lie.

WMULCH-1 is produced by unique process in which carbon black is pre-dispersed, then compounded with the basic resin through plastication.

It is widely used in film blowing , blowing plastic and fiber applications. Suitable for PP and PE materials.

It features low dosage, high blackness, good brightness, excellent heat resistance, outstanding dispersibility and tinting power, and minimal impact on the physical properties of the final product.

Specification traceability

Start from the film, not from the pellet

Most masterbatch data sheets answer the wrong question. They describe the pellet, while buyers are judged on the film.

Each row below starts with something that happens in the field or on the line, and traces it back to the masterbatch parameter that controls it.

Field function Specification — what the black layer does

What the black layer actually does in the field

Light exclusion. Weeds need photosynthetically active radiation to establish.

An opaque film denies it to them. The benefit depends entirely on uniformity : a thin strip or a poorly dispersed zone is a light leak, and the light leak becomes  weedy patch in few weeks.

Heat behaviour : the part that is usually described wrongly.

Black film is often called the warming mulch, and the measurement is more interesting than the description.

Because black absorbs most incident solar radiation at the film surface instead of transmitting it, soil under black film is not much warmer than bare soil during the day,

and under some conditions it is slightly cooler.

The real difference appears at night: soil beneath black film typically stays 0.5–4 °C above bare ground, and black film warms soil to working depth of around 8–10 cm.

Clear film behaves in the opposite way, running roughly 2–10 °C above bare soil by day.

That is why clear film is chosen where maximum early-season warming matters and weeds can be controlled by other means, and why black remains the most widely used mulch colour worldwide.

Indicative ranges compiled from extension-service field guidance (NC State Extension; New Mexico State University Extension; Washington State University Small Fruit Horticulture Program).

Real values vary with depth, soil moisture, film-to-soil contact, latitude and season.

Polymer protection. Carbon black shields polyethylene physically rather than chemically — it screens ultraviolet radiation instead of being consumed by it.

In outdoor exposure comparisons, unpigmented polyethylene loses useful mechanical properties in under a year, while polyethylene carrying a properly dispersed 2.0–2.5% carbon black load lasts well over two years.

Two conditions decide whether that protection actually materialises, the carbon black must be fine, and the particles must be separated from one another.

Coarse or agglomerated carbon black leaves parts of the film effectively unshielded, and those are the areas that fail first.

Moisture retention. The film's barrier function is mechanical, not chemical , the pigment contributes nothing directly.

What matters is that the film stays intact and in contact with the soil for the whole season. A film that develops pinholes in week three has stopped earning its cost long before harvest.

Failure modes 

What makes mulch film fail  and which part of the masterbatch is responsible for

Field failures are usually blamed on the film. Tracing them back to the masterbatch is faster than arguing about it, and it tells you what to test on the next delivery.

If you are diagnosing the failure right now, send us the film sample and the line log. We will return the written specification review rather than just quotation.

Technical Parameter of Black Masterbatch WMULCH-1

Line commissioning

Commissioning WMULCH-1 on your blown film line

Five steps as below : 

1. Start in the middle , not at the edge. 

Begin with 5.5–6.0% let-down, which lands at 2.5–2.7% carbon black in the film. Qualifying at the extremes first tells you nothing about where you will actually run.

2. Blend properly.

Tumble blend with the base resin for 3–5 minutes before the hopper.

Above roughly 800 kg/h, use gravimetric dosing rather than volumetric , the accuracy of the feeder is a bigger variable at that throughput than the masterbatch itself.

3. Stay inside your own temperature window.

WMULCH-1 is PE carrier masterbatch,  run it inside the profile you already use for your base resin.

For LDPE and LLDPE mulch lines this generally sits in the 160–215 °C range, and we recommend capping sustained melt temperature at 230 °C to protect the carrier.

No pre-drying is needed under normal storage; if the masterbatch bags have been exposed to humidity above 80% RH, pre-dry at 70 °C for 2 hours.

4. Read the bubble.

Check gauge uniformity across the web, look for gels and specks under transmitted light, and confirm the bubble is stable at your target line speed.

Take samples from both edges and the centre, not just from the middle. 

5. Qualify before you scale.

Run the light-transmittance check to ASTM D1003 and carbon black content to ASTM D1603 on the film sample.

If the gauge is below 15 μm, add one microtomy dispersion check on the first roll at that thickness, dispersion is the specification you are really buying.

Scale to production after two consecutive stable rolls.

When you switch back to natural resin, purge with an HDPE compound to clear residual pigment from the screw flights.

The above instructions are based solely on general models or laboratory experience.

The specific methods and results need to be adjusted and tested by the buyer according to their own equipment, processing conditions, materials and other various factors.

FAQ

Questions we are asked before ordering

Your published let-down for film is 4–8%. Other suppliers quote 1–3%. Why the difference?

What protects the film is the carbon black that ends up inside it, and the same let-down produces very different film-level results depending on how concentrated the masterbatch is.

Work backwards from the 2.0–3.0% carbon black your film needs, using the formula above, and ask every supplier for that same figure: carbon black in the film at their recommended dose.

It is the only number that travels.

Can I compare melt flow index values between suppliers directly?

Only when the test conditions match. MFI is measured at  specified temperature and load, and 190 °C / 10 kg and 190 °C / 21.6 kg are different tests whose results are not interchangeable.

Ask for the condition alongside the value, and check that the masterbatch sits within roughly ±15% of your base resin.

Will WMULCH-1 work in calcium carbonate (CACO3) filled mulch formulation? 

Yes. The concern with filled formulation is total inorganic load reaching the screen pack, and because ash is kept low this masterbatch adds little to what the filler already contributes.

If your filler level is high, run the first roll with  fresh screen pack and log the pressure rise , that reading tells you more than any data sheet.

How thin can the film go and still be fully opaque?

Opacity is carbon black level multiplied by gauge, so there is  practical floor.

Inside the agronomic ceiling of about 2.5–3.0% carbon black in the film, below roughly 15 μm the margin gets tight, and dispersion quality rather than dosage becomes the limiting factor.

Tell us the gauge you need to hit and we will tell you what is realistic — including when the answer is that a thicker gauge is the better commercial decision.

What happens if I overdose?

Above about 3% carbon black in the film, UV protection barely improves while tensile strength and elongation at break start to fall.

You also increase screen loading and cost. Over-dosing is  common and easily avoidable cause of film that tears during laying or during removal.

How do I confirm the carbon black level in my finished film?

ASTM D1603 on a film sample.

Take samples from both edges and the centre of the web  edge-to-centre variation is the quickest tell on dispersion quality, and it is far more informative than a single average.

Does the black fade during the season?

Carbon black screens ultraviolet radiation physically and is not consumed the way an organic absorber is, so it does not fade out of the film.

If you see chalking or surface change over the season, that points to insufficient carbon black in the film or an exhausted stabiliser package, not to the pigment disappearing.

What is the shelf life, and how should it be stored?

Store in a dry, enclosed, cool space away from UV and direct sunlight, and reseal opened bags.

Sealed pellets hold their performance for a long period; moisture is the real risk, not age. If a bag has been open in a humid warehouse, pre-dry at 70 °C for 2 hours.

Can you supply a black masterbatch for soil-biodegradable mulch film?

Not this grade. WMULCH-1 is  polyethylene carrier masterbatch for conventional polyolefin film.

Soil-biodegradable films built on PBAT, starch or PLA systems need a matched carrier and a different stabiliser strategy.

Ask us anyway — we would rather point you to the right formulation discussion than sell you the wrong grade.

Packing and Storage 

25kg/bag, PE or Composite Paper bag

Stored under dry, enclosed and cool conditions, protected from UV rays and/or direct sunlight. After used, the opened packaging must be resealed properly to prevent the product from absorbing moisture, which could affect its performance.

Note 

The technical results are typical values and are provided for customer reference only. They are not to be regarded as a guarantee of minimum or maximum quality specifications.