The Compostable 7003 Clarity Profile/Cast Film Compostable PLA Blend is a cast-film grade based on polylactic acid and a compostable copolyester modifier. It is intended for chill-roll extrusion lines producing clear, printable, heat-sealable webs that must comply with industrial composting standards. The 7003 designation refers to the clarity cast-film formulation within the broader compostable polyester portfolio, not to a blown-film or oriented-film product. The grade is positioned for applications where haze must remain below 3% after converting and where disintegration must meet EN 13432:2000 or ASTM D6400-23. Film properties depend on rapid solidification on a polished chill roll and on controlled pellet moisture below 250 ppm before extrusion. The copolyester modifier reduces the brittle fracture behaviour of unmodified PLA homopolymer while retaining sufficient modulus for label facestock, envelope windows, and clear compostable packaging.

Nominal film thickness ranges from 20 µm to 80 µm. Converters running below 20 µm should verify winding tension and edge trim behaviour because the cast PLA-blend web has higher modulus than PBAT-rich blown film. Density is controlled at 1.24–1.26 g/cm³ to ISO 1183-1:2019. Melt volume-flow rate at 190 °C and 2.16 kg is typically 8–12 cm³/10 min per ISO 1133-1:2022. Optical performance is verified by ASTM D1003-21; haze is controlled to 2.0–3.5% and total luminous transmittance is above 90% for 23 µm film. The property window is not a universal PLA value; it is linked to the d-lactide content, modifier loading, and moisture history of this specific grade.

Why does 7003 require a tighter extrusion and drying envelope than commodity LDPE?

Processing the 7003 blend on a cast line is governed by hydrolytic degradation rather than thermal oxidation alone. Pellets must be dried to below 250 ppm residual moisture using a desiccant dryer with a dew point at or below -40 °C. At hopper residence times above 4 h on a humid production floor, surface moisture uptake can exceed 500 ppm within 2 h when ambient relative humidity is above 60%. Hopper capacity should therefore be matched to line throughput, and a closed conveying system is preferred. Extrusion is typically performed on a single-screw extruder with 30:1 L/D and a barrier screw containing Maddock mixing elements. The melt-temperature set point should remain between 190 °C and 210 °C, with die temperature no more than 5 °C above the melt-temperature set point. Prolonged residence time above 230 °C promotes lactide formation and rapid molecular-weight reduction, even when the resin appears thermally stable by thermogravimetric analysis under nitrogen.

The chill-roll temperature is the primary optical control. A roll surface at 15–25 °C freezes the amorphous surface before spherulite growth can scatter light. Below 12 °C condensation creates surface pits and transfer defects, while above 30 °C the film becomes hazy and blocking-prone. The practical roll-setting window is therefore approximately ±5 °C around the optimized set point. Roll-surface thermocouple calibration should be checked at shift start before line speed is increased. Air gap between the die lip and roll nip is maintained at 8–12 mm; excessive air gap increases neck-in and machine-direction orientation, producing anisotropy and edge waste. Die gap is normally set between 0.8 mm and 1.2 mm for 20–50 µm film to keep draw ratio between 10:1 and 25:1.

Specific throughputs observed on production lines with 45 mm extruders typically fall between 6 kg/h/cm and 9 kg/h/cm of die width. Running below 4 kg/h/cm lengthens residence time and can trigger viscosity loss. Melt pressure at the breaker plate is normally 80–140 bar; a rising pressure trend without temperature change indicates gel accumulation on screen packs or degraded transition material. Operators should avoid purging with polyolefins because incompatible transition layers reduce film clarity and delaminate during slitting. Batch-to-batch variation in melt volume-flow rate should be monitored within ±1.5 cm³/10 min because an upward drift can produce gauge variation without a visible screw-speed change. If melt pressure drops by more than 10% at constant screw speed, the charge is either moisture-contaminated or thermally degraded; the corrective action is to stop feeding and purge with fresh dried material.

On a 45 mm extruder with a 300 mm coat-hanger die, neck-in of 10–15% of die width is observed when the air gap exceeds 10 mm. The melt exhibits pseudoplastic flow under cast-film shear rates. Published PLA melt rheology data show a power-law index of approximately 0.6–0.8 over apparent shear rates from 100 s⁻¹ to 1,000 s⁻¹, but the exact value for this modified grade should be confirmed by capillary rheometry per ISO 11443:2021 before die design changes are made.

Industrial composting certification thresholds for the 7003 grade

Compostability is not inferred from polymer chemistry alone. The grade is formulated to satisfy EN 13432:2000, ASTM D6400-23, and ISO 17088:2021 when converted within specified thickness, ink coverage, and laminating-adhesive limits. Under EN 13432:2000, organic carbon must be converted to CO₂ by at least 90% within 180 days relative to a positive control. After 12 weeks of controlled composting, no more than 10% of the original dry mass may remain on a 2 mm sieve. Ecotoxicity testing uses plant emergence and growth endpoints equivalent to OECD 208. Under ASTM D6400-23, aerobic biodegradation is assessed by ASTM D5338-15, and disintegration is assessed by ASTM D5929-18 or equivalent. Heavy-metal limits for composting are commonly compared with 40 CFR 503.13 Table 3 or national compost standards. Certification is lot- and conversion-dependent; a heavily printed web may disintegrate but still fail ecotoxicity if ink pigments or print coatings contain non-compostable residues.

The blend should not be processed on lines previously purged with PVC or acetal resins unless a complete PLA-compatible purge is performed. Residual PVC in hot-runner or die galleries degrades above 180 °C and can contaminate the compostable film. Storage should avoid direct sunlight and high humidity. Unopened pellets stored at 30 °C and 50% RH are typically stable for 12 months. Opened bags should be re-sealed or consumed within 8 h under ambient conditions above 60% RH. The film is not suitable for direct contact with high-free-water products without a barrier coating; water-vapor transmission rate for a 20 µm web is typically 300–500 g/m²·day at 23 °C and 85% RH. Published data for prolonged sub-zero food storage in this specific configuration is limited, so package-specific testing under ISO 11607 or ASTM F1929 is required when a sterile barrier or frozen-food package is converted.

When haze remains below 3%, inspection lighting and roll geometry become process variables

Clarity is measured as haze per ASTM D1003-21 using an integrating-sphere spectrophotometer with CIE Illuminant C. The method records the fraction of transmitted light deviating by more than 2.5° from the incident beam. A 23 µm film with haze of 2.5% can still appear milky if the scattered fraction is concentrated at narrow angles below 2.5° because human inspection under 500 lux LED lighting detects low-angle diffuse reflectance differently from the integrating sphere. The 7003 low-haze profile depends on rapid solidification, low melt temperature, and a polished chill-roll surface with roughness Ra between 0.02 µm and 0.05 µm. If roll roughness exceeds 0.1 µm, surface replication can raise haze by 1–2 percentage points and create visible diffuse reflection under warehouse inspection.

Clarity is not equivalent to gloss. A film can have high gloss but elevated wide-angle scattering from internal morphology or surface roughness. This distinction is important for lamination because adhesive wetting is affected by surface topography rather than bulk haze. Converters inspecting clear labels under 500 lux LED lighting report fewer subjective “milky” rejections when total transmittance exceeds 90% and haze is below 3%. However, line-stop events that leave the web against a hot roll for more than 30 s can produce visible bands even when average haze remains in specification. The defect is not captured by a single haze measurement; it requires continuous roll-quality inspection or periodic retained samples at shift change.

Substituting 7003 for PBAT/PLA blown-film grades changes die-lip shear and thermal history

Compared with PBAT-rich blown-film compostables, the 7003 cast film is stiffer. Tensile modulus is in the 2,500–3,000 MPa range versus 200–400 MPa for many PBAT films. It also displays lower machine-direction elongation at break than very soft PBAT-rich webs and higher dead-fold character. Blown-film extrusion of PLA blends involves an air ring and a frost line; cast film transfers heat through the chill roll, producing a different crystalline morphology and lower thickness variation. A cast line can hold thickness tolerance at ±3% on 20–50 µm films, while blown lines typically hold ±8–12%. This thickness uniformity is relevant for print registration, unwind tension control, and automated envelope insertion. The 7003 grade is not intended for stretch wrap; plastic deformation begins at low elongation and does not provide the elastic recovery of LLDPE-based stretch products.

Compared with an unmodified PLA homopolymer cast film, the 7003 blend contains a compostable polyester impact modifier. The modifier shifts elongation at break from the 3–10% typical of brittle PLA homopolymer to 150–250%, with a 10–20% reduction in tensile modulus. This is a deliberate trade-off. In label facestock converting, lower modulus can reduce die-cutting snap-back, but it can also increase film stretching under high rewind tension. The grade differs from ordinary PBAT/PLA blown film in that it may be oriented in the machine direction on a single-stage MDO unit at 60–70 °C to improve stiffness and moisture-vapour barrier; transverse orientation is limited because the cast web has minimal bubble stability and cannot be expanded like a blown tube.

Typical converting uses include clear compostable produce bags, label facestock, envelope windows, floral wrap, and carton windows. For a produce bag on an intermittent-motion sealing machine, seal initiation at 85–100 °C allows dwell times of 0.3–0.5 s without film puckering. For label facestock, corona treatment to 42–46 mN/m is maintained for UV flexographic inks. Water-based acrylic pressure-sensitive adhesives have been used, but converters must verify adhesive pH because strongly alkaline adhesives can attack PLA ester linkages during storage. For compostable envelope windows, the reduced thickness variation of the cast web allows automated insertion at high speed; converters should nevertheless verify fold-crack resistance using ISO 8776:2020 or a customer-specific folding sequence because PLA-blend films can whiten at fold lines under low-temperature folding below 10 °C.