| HS Code | 425665 |
| Biodegradability | Fully biodegradable in soil within 60-180 days under natural conditions |
| Watersolubility | Soluble in water with solubility depending on hydrolysis degree and temperature |
| Filmformingability | Excellent film-forming properties producing uniform and continuous thin films |
| Tensilestrength | Typically 20-50 MPa depending on molecular weight and plasticizer content |
| Elongationatbreak | Ranges from 100% to 400% showing good flexibility for mulching applications |
| Oxygenpermeability | Low oxygen permeability providing effective gas barrier properties |
| Watervaportransmissionrate | Moderate to high WVTR enabling moisture regulation within the soil |
| Uvresistance | Sensitive to UV degradation requiring stabilizers for outdoor field durability |
| Opticaltransparency | Transparent to visible light allowing light penetration for soil warming |
| Thermalstability | Stable up to 200°C in processing but degrades above melting point near 230°C |
| Thicknessrange | Commonly manufactured in 15-30 μm thickness for agricultural mulch films |
| Toxicity | Non-toxic and safe for soil microorganisms, plants, and agricultural ecosystems |
As an accredited Polyvinyl Alcohol (PVA) for Agricultural Mulch Films factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packaged in 25 kg moisture-resistant bags, PVA resin for agricultural mulch films ensures easy handling and storage. |
| Container Loading (20′ FCL) | 20′ FCL loading: 25kg PVA resin bags on pallets, shrink-wrapped, securely braced to prevent shifting during transit. |
| Shipping | Ship Polyvinyl Alcohol (PVA) in sealed, moisture-barrier bags or containers to prevent hydration. Use clean, dry containers or trucks, avoiding humid conditions. No dangerous goods classification; however, keep away from water sources and store at moderate temperatures. Secure pallets during transit to prevent damage and spillage. |
| Storage | Store Polyvinyl Alcohol (PVA) in a cool, dry, well-ventilated area, away from direct sunlight, heat, and ignition sources. Keep containers tightly sealed to prevent moisture absorption, as PVA is water-soluble. Avoid dust accumulation and contact with oxidizing agents. Under proper conditions, shelf life is typically 12–24 months. |
| Shelf Life | Shelf life is typically 1–2 years if stored dry, cool, and away from direct sunlight, maintaining film-forming properties. |
Melt-processing polyvinyl alcohol for mulch film production imposes a strict thermal constraint rarely encountered in conventional polyolefin extrusion: the polymer’s substantial hydrogen-bonding density depresses the degradation onset temperature to within 15–25°C of its crystalline melting range, creating a processing window where screw configuration, barrel temperature profiling, and residence-time distribution must be balanced against the risk of backbone scission and concomitant loss of molecular weight. Industrial-scale compounding on corotating twin-screw extruders with an L/D ratio of 40:1 to 44:1 has demonstrated that partially hydrolyzed grades with a degree of hydrolysis between 86 mol% and 89 mol% and a 4% aqueous-solution viscosity of 20–30 mPa·s at 20°C can be plasticized with a polyol system—typically a combination of 15–25 wt% glycerol and 5–10 wt% sorbitol relative to total polymer weight—to shift the melt-flow onset below 175°C, while fully hydrolyzed grades (≥98 mol%) require water-assisted extrusion with barrel venting to prevent catastrophic decomposition. Formulations targeting EN 17033:2018 and ISO 23517:2021 compliance for soil-biodegradable mulch films commonly combine 40–60 wt% PVA with thermoplastic starch, poly(butylene adipate-co-terephthalate) (PBAT), or polylactic acid (PLA) as the balance, with PVA serving both as a process aid that improves polar-filler dispersion and as the primary contributor to the film’s oxygen-barrier and anti-static characteristics. On single-screw blown-film lines with a 30:1 L/D screw and a dual-lip air ring, melt temperatures are maintained within 180–195°C at the die head, and pre-drying of the compound to a moisture content below 0.3 wt% in a desiccant dryer with a −40°C dew point is mandatory when ambient relative humidity exceeds 55%; failure to do so results in steam bubble formation and gel-particle defects visible as translucent fisheyes in the finished web. The produced film—typically black masterbatched with 2–4 wt% carbon black of primary particle size 20–50 nm—is slit and wound into rolls of 1.0–1.8 m width and 12–25 μm gauge for in-row vegetable mulching, where the PVA component ensures that degradation commences within 90–180 days of soil incorporation under mesophilic conditions as validated by the respiration test method of ISO 17556:2019. Published data for this specific configuration is limited to pilot-scale trials; variations in starch botanical origin (maize vs. potato) have been observed to alter the equilibrium moisture uptake of the melt by ±1.2% at 50% RH, directly affecting the blow-up ratio stability required for consistent layflat width.
Liquid mulch formulations based on aqueous PVA solutions are employed where mechanical laying of prefabricated film is impractical, such as on slopes exceeding 15° grade, in wind-erosion-prone seedbeds, or in orchards with irregular trunk spacing. The working dispersion is prepared by dissolving cold-water-soluble PVA grades—characterized by a degree of hydrolysis of 86–88 mol% and a 4% solution viscosity of 5–15 mPa·s at 20°C—in water at a concentration of 5–10 wt%, often with 0.5–2 wt% of a defoamer (silicone-free acetylenic diol surfactant) and, when UV-stability is required beyond 6 weeks, 0.1–0.3 wt% of a hindered-amine light stabilizer (HALS) dispersed via a co-solvent. Application is performed using tractor-mounted hydraulic sprayers delivering 3–6 L/m² through flat-fan nozzles at 2–3 bar pressure, producing a continuous, self-leveling film that cures within 2–4 h at ambient temperature and 60% RH, with a final dry-film thickness of 20–50 μm. No unified ISO specification exists specifically for spray-applied biodegradable mulch; conformity is typically assessed under test protocols aligned with the soil-biodegradation screening of ISO 17556:2019 and the ecotoxicity criteria of OECD 208 (Terrestrial Plant Test: Seedling Emergence and Seedling Growth), while mechanical performance is measured against the soil-cover function requirements of EN 17033:2018 adapted for in-situ deposition. The principal limitation of this approach remains the tensile strength of the film in a hydrated state, which rarely exceeds 1.5 MPa at 20°C and 90% RH, rendering it unsuitable for locations subject to heavy rainfall within the first 48 h after application; re-spraying of localized tear zones is a documented operational necessity in commercial tea plantation trials on Sri Lankan hillsides.
Integrating pre-emergent herbicides directly into the polymer matrix of a biodegradable mulch film eliminates the separate application pass, but it introduces a mass-transfer control problem: the release rate of the active ingredient must remain below phytotoxic thresholds for the crop while maintaining a herbistatic concentration at the soil surface over a 4–8 week critical weed-emergence window. PVA serves as a hydrophilic carrier that can be blended with a hydrophobic controlled-release modifier such as polycaprolactone (PCL) or PBAT at a ratio of 70:30 to 50:50, with the herbicide compounded into the PVA phase at 1.0–3.0 wt% of total formulation weight; metolachlor and pendimethalin have been successfully incorporated with recovery rates exceeding 92% during the extrusion step when barrel temperatures are held at 160–175°C. The film is produced on a cast-film line with a 25:1 L/D single-screw extruder and a chill-roll temperature of 15–20°C, followed by in-line slitting to widths of 0.9–1.5 m and rolling at 15–20 μm gauge; post-production off-gassing in a ventilated warehouse at 25°C for 72 h is required to reduce residual solvent levels below analytical detection limits. Regulatory compliance is bifurcated: the film substrate must meet the biodegradation and ecotoxicity endpoints of EN 17033:2018, while the herbicide-loaded article is treated as a plant protection product under Regulation (EC) No 1107/2009 and requires zonal authorization with residue data demonstrating that active-substance migration into the crop rhizosphere remains below the soil metabolite maximum residue limit established in Part A of Annex III to that Regulation. Terminal products are marketed as pre-printed, color-coded films (e.g., brown for metolachlor, blue for pendimethalin) for tomato, pepper, and cotton ridge-planted systems, where the film’s disintegration synchronizes with the crop canopy closure that naturally suppresses late-season weeds.
When a fumigation protocol must be coupled with mandated post-fumigation film removal—a contradiction that legislated biodegradable solutions cannot fully resolve—multilayer films containing a central PVA barrier layer are coextruded to permit rapid volatile dissipation after a defined number of soil degree-days, after which the encapsulating outer layers delaminate. The structure is typically a three-layer A/B/A configuration where the core B layer comprises 20–30% of the total thickness and consists of a PVA compound plasticized with 12–18 wt% glycerin and melt-compounded with a maleic-anhydride-grafted polyolefin compatibilizer at 3–5 wt% to ensure adhesion to the outer layers of PBAT or poly(butylene succinate-co-adipate) (PBSA). Coextrusion through a multi-manifold die at a melt temperature of 185–200°C and a line speed of 80–120 m/min yields a film of 30–40 μm total gauge with a PVA layer as thin as 6–8 μm; the barrier contribution of PVA against methyl bromide and chloropicrin has been quantified through permeance measurements performed according to ASTM F739-12, showing a steady-state permeation rate reduction of 94% relative to neat PBAT films at 23°C and 50% RH. The film is classified under the broader category of soil-biodegradable mulch films per ISO 23517:2021, but certification bodies increasingly require additional proof of delamination-triggered degradation under the specific soil temperature and moisture conditions of the intended geographic region, typically assessed using the soil-burial and mass-loss documentation framework of ISO 17556:2019 with a pass criterion of ≥90% relative biodegradation within 24 months. Terminal products are used as single-season films for high-value crops such as strawberries and tomatoes in controlled-environment tunnels where regulatory authorities in the EU require demonstrable elimination of the fumigant-barrier function before the next planting cycle.
For specialty perennial crops with short harvest intervals—raspberry cane establishment, artichoke ratoons, or second-year asparagus—the standard 24-month biodegradation window of EN 17033:2018 may be contractually truncated by processor-driven sustainability programmes to 12 months or less, demanding accelerated in-soil disintegration that cannot be achieved by merely reducing film gauge. In such applications, PVA is incorporated into a PBAT matrix at a level of 30–40 wt% together with a pro-oxidant transition-metal stearate masterbatch at 0.5–1.0 wt%, and the film is produced on a high-stalk blown-film bubble with in-line annealing at 60°C to pre-stress the polymer chains, yielding a final film of 15 μm that will embrittle within 90 days of soil contact under temperate autumn conditions. Compliance is verified through the accumulated soil-temperature integral method described in Annex D of ISO 23517:2021, and the finished product is supplied as slotted micro-perforated rolls for mechanical laying on raised beds.
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A growing fraction of intensive horticulture operations has transitioned away from conventional low-density polyethylene (LDPE) mulch films toward water-soluble, biodegradable alternatives, driven by disposal cost reduction and the elimination of persistent microplastic accumulation. Among these materials, polyvinyl alcohol (PVA) occupies a distinct position due to its synthetic origin combined with full inherent biodegradability when appropriately formulated. Unlike starch blends or polylactic acid (PLA), PVA does not require microbial enzyme systems to initiate chain scission of a natural polymer backbone; instead, its carbon–carbon backbone is enzymatically cleaved by a phylogenetically narrow group of soil-borne bacteria and fungi after dissolution from the swollen film matrix. Commercially available grades suitable for mulch film extrusion span weight-average molecular weights (13,000 to 186,000 Da) and degrees of hydrolysis from 86 to 99 mol%, each combination dictating cold-water solubility, crystalline melting point, and film mechanical properties. Conformity with the core biodegradation standard EN 13432 and its soil-degradation annex, validated through ISO 14855-2 (controlled composting conditions) and ISO 17556 (soil burial), is routinely demonstrated for tailored PVA compounds, while ecotoxicity testing under OECD 208 confirms no inhibitory effect on seedling emergence.
The degree of hydrolysis—the molar percentage of acetate groups converted to hydroxyl groups on the polyvinyl acetate precursor—directly controls the crystalline/amorphous ratio and hence the temperature at which primary crystallites dissolve. Fully hydrolysed grades (≥98 mol%) exhibit a crystalline melting point near 230 °C and require aqueous temperatures above 80 °C for complete dissolution, rendering them unsuitable for a mulch film that must fragment and disintegrate under ambient soil moisture. Partially hydrolysed grades in the range of 87–89 mol%, such as those corresponding to Kuraray Poval 205, 217 or Sekisui Selvol 205, display a broad cold-water solubility window—dissolution onset as low as 10–20 °C—because residual acetate groups interrupt intermolecular hydrogen bonding. This solubility regime enables a designed mulch film to lose structural integrity after a pre-determined period of soil contact, typically 45–60 days under a maintained soil matric potential above −33 kPa. The relationship between degree of hydrolysis and disintegration is routinely mapped using a dissolution temperature test per JIS K 6726 and supplemented by film residue visual rating scales adapted from ISO 846.
| Hydrolysis (mol%) | Mw Range (Da) | Aqueous Dissolution Temperature (°C) | Typical Film Application Window |
|---|---|---|---|
| 87–89 | 13,000–23,000 | 10–25 | Short-cycle leafy greens (30–50 days) |
| 87–89 | 85,000–145,000 | 15–30 | Strawberries, cucurbit crops (60–120 days) |
| 91–93 | 145,000–186,000 | 35–55 | Delayed disintegration; row covers in wet climates |
| ≥98 | 145,000–186,000 | >80 | Not recommended for soil-degradable mulch; used for temporary water-soluble packaging |
The selection of molecular weight within a given hydrolysis band introduces a secondary control on mechanical life. Higher molecular weight grades (> 100,000) provide sufficient melt strength for blown film extrusion at die gaps of 0.8–1.5 mm and yield a tensile strength of 30–40 MPa when tested per ASTM D882 (50 mm/min, 23 °C, 50 % RH), but the slower dissolution kinetics of a high-viscosity, high-molecular-weight matrix may delay full disintegration beyond the growing season. Thus, a grade balance is struck: a medium molecular weight, partially hydrolysed PVA (85,000–100,000 Da, 88 mol% hydrolysis) is widely adopted for films intended to degrade within 90–120 days under temperate soil conditions.
Conversion of PVA granulate into a thin-gauge agricultural film demands a narrow processing corridor. The polymer must be pre-dried to a residual moisture content below 0.3 wt% using a desiccant dryer with a dew point of −40 °C or lower; failure to do so results in steam hydrolysis during plastication, leading to bubble instability and pinhole defects. Extrusion is typically carried out on a single-screw or co-rotating twin-screw extruder with an L/D ratio of 30:1, equipped with a grooved feed section and a barrier screw to manage the polymer’s low bulk density. Barrel temperature profile is maintained between 180 °C (feed zone) and 210 °C (die zone); exceeding 220 °C triggers thermal degradation via chain dehydration and formation of conjugated polyene sequences, evidenced by yellowing and an abrupt drop in melt viscosity measurable by ISO 1133-1:2022 melt flow index procedure. The melt is extruded through an annular die with a die gap of 0.8–1.2 mm and blown at a blow-up ratio of 2.0–3.0 to achieve a final film thickness of 25–50 µm.
Because unplasticized PVA film is stiff below its glass transition temperature (Tg ≈ 80 °C), polyol plasticizers—predominantly glycerol, sorbitol, or a glycerol-polyethylene glycol blend—are incorporated at 15–30 phr. The critical processing defect is plasticizer migration to the film surface, which causes blocking on the roll and erratic field-wetting behaviour. Migration rate is minimised by selecting a plasticizer with a Hansen solubility parameter distance (Ra) from PVA of less than 8 MPa1/2 and by maintaining a blow-up ratio and frost-line height that promote rapid vitrification of the outer film surface. Real-time monitoring of surface stickiness via a tack test adapted from ASTM D2979 is common on production lines. Published data for this specific configuration is limited, but industrial practice confirms that glycerol-based systems at 20 phr yield a film with an elongation at break of 200–300 % (ASTM D882) and a dart drop impact resistance of 150–250 g (ASTM D1709 method A). These values approximate those required for mechanical mulch laying equipment operating at 3–5 km/h.
Field observations from multi-year trials on drip-irrigated tomato crops in Mediterranean climates confirmed that film laying with a tractor-drawn bed shaper and mulch layer was successful when the film’s secant modulus at 1% strain (ASTM D882) remained above 500 MPa in the machine direction. Films below this threshold exhibited neck-in at the soil surface, tearing at the planting hole punctures. One proprietary PVA mulch grade, cross-linked via a borate-diol equilibrium reaction in the melt to temporarily retard solubility, achieved a wet tensile strength retention of 40–50% after 24 h water immersion (23 °C), compared to 5–10% retention for an uncrosslinked control, enabling the film to withstand early-season rainfall without premature disintegration. This crosslinking approach, however, introduces a processing constraint: the borate level must be kept below 0.5 wt% to avoid gelation in the extruder head, and the compound must be purged immediately after the run to prevent corrosive die build-up.
The biodegradable mulch film market is segmented by polymer chemistry, each category exhibiting a different trade-off between soil-degradation kinetics, mechanical toughness, and vapour permeability. PVA is distinguished from starch-based thermoplastic blends (TPS) and polylactic acid (PLA) films by its dissolution-triggered degradation mode. TPS films, processed from destructurized starch with compatibilizers such as poly(butylene adipate-co-terephthalate) (PBAT), rely on microbial amylase activity to hydrolyse α-1,4-glycosidic bonds. While cost-competitive, TPS films are inherently brittle; elongation at break values rarely exceed 30% without a large synthetic co-polyester fraction. PLA mulch films, produced from poly(L-lactide) (PLLA) by cast extrusion, offer high clarity and sufficient strength but degrade primarily through abiotic hydrolysis above the glass transition (55–60 °C), meaning soil degradation at ambient temperature is exceedingly slow—often requiring 24–36 months for complete visual disappearance, and residues fail the EN 17033 ecotoxicity criteria unless industrial composting is applied.
PVA, by contrast, exhibits a half-life in aerated soil slurry of 30–45 days under ISO 14855-2 respirometric conditions when inoculated with Sphingomonas sp. and Pseudomonas sp. consortia previously acclimatised to PVA-contaminated environments. The key difference for the farmer is that PVA film fragments can be ploughed directly into the soil post-harvest, eliminating labour and disposal costs associated with polyethylene film removal—estimated at €150–400 per hectare depending on crop and region. A comparative property matrix (see table) highlights the position of a 25 µm medium-molecular-weight, partially hydrolysed PVA film relative to competing biodegradable alternatives and reference LDPE.
| Property | PVA (88 mol% hydrolysis) | PLA | TPS/PBAT Blend (60/40) | LDPE |
|---|---|---|---|---|
| Tensile strength, MD (MPa) – ASTM D882 | 30–40 | 45–60 | 15–25 | 18–25 |
| Elongation at break, MD (%) – ASTM D882 | 200–300 | 3–10 | 200–500 | >600 |
| WVTR (g/m²·day) – ASTM E96 desiccant method, 38 °C, 90 % RH | 150–300 | 5–15 | 50–200 | 1–5 |
| Soil degradation (visual disappearance) – ISO 846, burial, 25 °C | 60–120 days | >24 months | 90–180 days | Does not degrade |
| Standard compliance | EN 13432, EN 17033, ASTM D6400 | EN 13432 (compostable), ASTM D6400 | EN 13432, EN 17033 | Not biodegradable |
The high water vapour transmission rate of PVA films represents a functional advantage in humid horticultural environments because it prevents condensation-induced fungal sporulation on the leaf underside, a documented problem with LDPE tunnels. On the other hand, in arid open-field cultivation, the same permeability accelerates soil moisture loss, and PVA must be combined with a thin, degradable hydrophobic coating—often a natural wax emulsion applied inline—to balance transpiration against water retention. No universally accepted standard for such a hybrid structure exists, and field data remains crop-specific.
The soil biodegradation pathway of PVA relies critically on water availability to swell the amorphous domains, enabling extracellular PVA oxidase and dehydrogenase enzymes to access the polymer backbone. Under rain-fed conditions where soil water potential falls below −1.5 MPa (the conventional permanent wilting point for many crops), film moisture content drops below the 5–8 wt% threshold necessary for microbial colonisation. In semi-arid field trials conducted on cotton in the Texas High Plains, PVA mulch fragments remained partially intact at the end of a 180-day growing season, with percentage mass loss measured by ISO 17556 achieving only 30–50% compared with >90% in irrigated plots. This moisture dependency—absent in PLA or PBAT films that degrade by hydrolytic chain scission independent of dissolution—constitutes a primary operational boundary: PVA mulch is contraindicated for purely dryland agriculture unless irrigation is applied even after crop senescence to drive the microbial mineralisation phase.
Furthermore, soils with a cation exchange capacity exceeding 25 cmol(+)/kg and high free calcium ion content can precipitate PVA via multivalent ion bridging, forming a temporary gel layer at the film-soil interface that slows dissolution without altering the ultimate biodegradation endpoint. This effect has been observed in calcareous Mediterranean terra rossa soils, where disintegration time lengthened by 15–25% relative to quartz-sand reference soils in identical biodegradation tests. Formulators address this by incorporating a low level (1–2 wt%) of sodium hexametaphosphate as an ion-chelating additive, verified to prevent gelation through melt rheometry measurements at 0.1 rad/s angular frequency. However, such additives must pass terrestrial ecotoxicity screening per ISO 11268-1 (earthworm acute toxicity) and ISO 11269-2 (plant emergence and growth) before the film can be certified under the EN 17033 soil-biodegradable mulch standard.
