Greenhouse Film: Weatherability Under High Sulfur, Chlorine and Temperature

I. The triple harshness: sulfur, chlorine and high temperature are additive, not parallel

The three together are the hardest problem. Looked at separately, each has a countermeasure. The difficulty is that they accelerate each other: sulfur first poisons the light stabilizer, high temperature then drives both the poisoned product and the residual additive away, while the unprotected PE backbone simultaneously chain-scissions under UV and high temperature. So "just add more HALS" is never the answer—the amount added would itself be consumed. One must chemically replace the "protonatable basic nitrogen."

II. Under co-extrusion, the three layers face completely different aging pressure

Modern PO film is generally 3- or 5-layer co-extruded, each layer with a different function: the outer layer faces the sun and handles anti-aging and anti-puncture; the middle layer handles mechanical strength and thermal insulation; the inner layer is the anti-drip/anti-fog layer (PO film uses a coating process). The additive distribution and aging pressure differ by layer.

The greenhouse film's inner surface is long under saturated humidity and a condensation-water environment, where fumigant pesticides preferentially settle—the main reason inner-layer aging is often faster than outer.

III. "Clearly dosed yet still bursts" — four real reasons

1. The light stabilizer has already been protonated and deactivated

This is the primary reason and most easily misjudged as "insufficient dosage." More dosage only delays deactivation, not solving the structural problem. Discrimination method: take film samples of the same formulation; treat one group with sulfur/chlorine fumigation then xenon aging, and the other with xenon aging directly; compare the mechanical-retention difference. A large difference = severe deactivation.

2. Already consumed during processing

Blown-film temperature 190–220°C; excessive residence time or shear lets HALS be consumed and degraded already in the melt stage. Factory test may still pass, but by the time it reaches the user the margin is insufficient. Response: choose high-Mw products with good thermal stability, use masterbatch pre-dispersion for uniform dispersion, and shorten high-temperature residence.

3. Synergistic consumption of thermal and photo oxidation

At 60–80°C in the shed, the antioxidant is rapidly exhausted while the backbone, protected by the light stabilizer, still slowly thermally oxidizes. When the antioxidant is later exhausted, performance drops off a cliff. Response: pair primary/secondary antioxidants; AO-427, with outstanding thermal stability and processing-stabilization function, covers both ends.

4. Physical hot spots and stress fatigue

At film-frame contact points temperature can reach 80°C, forming hot spots; on windy days the film continuously flaps against the frame, and local repeated stress produces fatigue cracks. This is a structural problem, not an additive problem—but engineering can significantly extend life by thermally insulating at film-frame contact (white plastic-tape binding or a water-based coating).

IV. Solution & acceptance: judge by industry-standard methods

4.1 Criterion: T/CPPIA 12-2021

Tiangang is one of the drafting units of this standard. T/CPPIA 12-2021 is under the purview of the China Plastics Processing Industry Association; among its 19 drafting units is Beijing Tiangang Auxiliary Co., Ltd. The drafters include Qin Lijie, Secretary-General of the China Agricultural Plastics Application Technology Society, Sinopec Beijing Chemical Research Institute, and leading greenhouse-film enterprises such as Huadun Xuehua, Yuxi Xuri, Kelun Plastics and Shandong Qingtian. In other words, the industry yardstick used to judge "whether a pesticide-resistant greenhouse film passes" was co-authored by Tiangang.

4.2 Test procedure (the real challenging test)

1. Sample grouping: prepare two groups each in machine and transverse directions, one as control.
2. Sulfur/chlorine pesticide contact treatment: fumigation or immersion. For sulfur-fumigation-resistant film, superpose daily sulfur fumigation for 1–3 months of intensified conditions, simulating the real greenhouse environment—this is the true meaning of "high sulfur, high chlorine."
3. Xenon-arc artificial-weathering aging per GB/T 16422.2: irradiance 0.51 W/m² (340 nm), black-panel temperature 65±3°C, cumulative dose in kilo-ly (kly). Note the black-panel temperature of 65°C itself constitutes the third pressure.
4. Tensile property determination per GB/T 1040.3: measure tensile strength and nominal elongation at break, calculate retention relative to unaged sample, judge MD and TD separately.

Related base standards: PE mulch film complies with GB 13735; EVA greenhouse film with GB/T 20202; fully biodegradable mulch film with GB/T 35795.

4.3 Tiangang solution & products

V. Tiangang's own empirical data