The product designated as PLA film biaxially oriented/cast/shrink film polylactic acid comprises three conversion formats from poly(lactic acid) resin: biaxially oriented film (BOPLA), chill-roll cast film, and stretch-annealed shrink film. Film-extrusion grades are selected with melt-flow rate of 2-10 g/10 min at 210 °C under 2.16 kg load per ISO 1133-1:2022, density of 1.24-1.25 g/cm³ per ISO 1183, and D-lactide content below 4 mol% to regulate crystallisation. Thickness spans 15-150 µm across the product line: biaxially oriented grades are typically converted at 15-50 µm, cast grades at 20-150 µm, and shrink grades at 30-60 µm. Principal uses include compostable food-contact overwrap, flow-wrap seal layers, labels, twist wrap, lamination web, tamper-evident bands, and full-body shrink sleeves. Differences from petroleum-based films arise from the glass-transition temperature of PLA of 55-60 °C, moderate moisture barrier, and hydrolytic sensitivity during melt conversion.

On production biaxially oriented PLA (BOPLA) tenter lines, edge trim is amorphous and hydrolysis-sensitive; regrind addition at 10-25 % is possible only when the trim is re-dried to below 250 ppm moisture and melt-blended before the die. Clip fouling from low-molecular-weight lactide deposits creates tracking instability and requires periodic cleaning with alkaline detergent solutions; chlorinated solvents should be avoided because they can stress-crack PLA under residual orientation. Static discharge is controlled with ionizing bars at the cast unit and tenter entrance because PLA surface resistivity can produce web wander and dust pick-up under dry conditions or at line speeds above 150 m/min. Melt filtration at 20-40 µm is standard to remove gel particles and die-lip deposits that form after 4-6 h continuous extrusion. These bottlenecks are more pronounced than on polypropylene lines and require scheduled shutdown intervals for die and tenter clip maintenance.

Why Does Moisture Control Govern the Melt-Processing Window for PLA Film?

On production-scale conversion lines, undried PLA resin causes viscosity loss, bubble instability, and die-lip deposits because PLA hydrolyses at melt temperature. Resin suppliers specify pre-drying to below 250 ppm moisture, typically in a desiccant-wheel dryer with dew point ≤ -40 °C, drying air temperature of 80 °C, and residence time of 4-6 h. When storage RH exceeds 60 %, pre-drying is mandatory even if resin was supplied in moisture-barrier packaging. Moisture above 500 ppm produces measurable molecular-weight reduction at 200-220 °C melt temperature, observed as pressure loss at the die and lower tensile strength. Single-screw extruders with barrier screws and L/D 30:1-40:1 are used for cast and orientation feed; neat film grades do not require twin-screw compounding unless masterbatch or regrind dispersion is required. Melt temperature at the die is held at 200-210 °C for most grades; temperatures above 230 °C initiate lactide reformation, yellowing, and acetaldehyde generation. Residence time in hot end and die should remain under 10 min to limit degradation. Filtration through 20-40 µm breaker plates or candle filters removes gel particles generated by partial degradation. These constraints are tighter than for polypropylene or PET and constitute the main operational boundary for PLA film extrusion.

Biaxial Orientation Draw Ratios and Tensile Property Asymmetry

Biaxially oriented PLA film is produced by casting an amorphous sheet and stretching it in a tenter frame at preheat temperatures of 70-85 °C. The processing window is narrow: if preheat is below 65 °C, stress whitening and tearing occur; if above 90 °C, crystallisation competes with orientation and haze increases. Typical draw ratios range from 2.5:1 to 4.0:1 in machine direction and 3.0:1 to 5.0:1 in transverse direction, depending on grade and thickness. Annealing at 110-130 °C after stretching fixes orientation and raises thermal stability. Datasheet values for 20-25 µm biaxially oriented film under ASTM D882 commonly include tensile strength of 110-150 MPa in MD and 100-140 MPa in TD, elongation at break of 70-110 %, tensile modulus of 3.3-3.9 GPa, haze of 2-6 %, and gloss at 60 ° above 90. Orientation reduces water-vapour transmission rate by 30-50 % relative to cast film of the same thickness because strain-induced crystallinity densifies the amorphous phase. The main differences from biaxially oriented PET are lower modulus, lower continuous use temperature, and higher water-vapour transmission; BOPLA is therefore selected for renewable-content labels and twist wrap rather than retort or high-temperature barrier applications.

The narrow orientation window of BOPLA is a direct consequence of PLA crystallisation kinetics. At preheat temperatures above 90 °C, spherulites form within seconds and create haze; at temperatures below 65 °C, tensile stress during stretching exceeds the amorphous network strength. Draw ratios above 4.0:1 in either axis can cause microvoiding and loss of tear resistance, while draw ratios below 2.5:1 produce insufficient strain-induced crystallinity and higher shrinkage in storage. Annealing at 110-130 °C for 10-30 s fixes orientation and reduces unrestrained shrink at 100 °C from more than 5 % to below 2 %. These thresholds explain why BOPLA production requires tighter tenter control than biaxially oriented PET or polypropylene and why batch-to-batch variation in D-lactide content shifts the usable draw window.

Chill-roll cast PLA film is produced without intentional orientation by quenching a 200-210 °C melt on a polished roll held at 15-25 °C. Rapid cooling suppresses spherulitic crystallisation and yields an amorphous, transparent film with low haze of 1-4 % per ASTM D1003, high elongation of 250-500 % per ASTM D882, and low tensile strength of 35-60 MPa MD and 25-50 MPa TD. Cast PLA is used as heat-seal layers in flow-wrap and lidding because seal initiation occurs at 85-95 °C, lower than many BOPLA grades. Seal strength increases rapidly above 100 °C, but the narrow softening range requires precise jaw-temperature control; overheating above 120 °C causes film shrinkage and wrinkle at the seal. Cast film also serves as print webs, window patching, and thermoformable base film for trays. Cast PLA processing uses an air-knife or electrostatic pinning system to ensure contact with the chill roll. Without pinning, the low melt strength of PLA at 200-210 °C causes neck-in and thickness variation above ±5 %. Chill-roll surface temperature is maintained within ±2 °C; excursions produce blocking or differential crystallinity. For heat-sealable cast grades, the seal layer is often coextruded with a higher-D-lactide amorphous grade to lower seal initiation and reduce blocking at reel temperatures above 35 °C.

Shrink PLA film is manufactured by stretching the film at 65-80 °C and partially annealing while retaining frozen-in stress. Under ASTM D2732 free-shrink testing at 90 °C for 10 s, commercial grades are typically specified at 40-60 % in both MD and TD, with shrink initiation near 55-60 °C. The shrink window is lower and narrower than PVC or PETG shrink films, which allows use on heat-sensitive containers but demands tight tunnel-temperature control; exceeding 100 °C can induce crystallisation, shrink-force decay, and visual haze in PLA. Published shrink-force data for PLA sleeves is less standardised than for PVC or PETG; comparisons should be made using ASTM D2838 or ISO 14616 on identical thickness and seamed-tube geometry. PLA shrink film is used for tamper-evident bands, multipack collation, and full-body labels where industrial compostability is required. Shrink film line operators monitor preheat, stretch, and annealing temperatures independently. A temperature offset of ±3 °C in the stretch zone changes final free shrink by several percentage points because PLA orientation release stress drops rapidly as the film approaches 60 °C. If the film is quenched too quickly after stretching, shrinkage can be unstable; if annealed too long, shrink is reduced below specification. The double-bubble process permits higher MD/TD balance, while tenter-line shrink film gives higher TD shrink and is preferred for sleeve labels. Edge trim from shrink grades contains oriented crystallites and is more difficult to re-disperse than cast trim.

Relative to biaxially oriented PET, BOPLA exhibits lower tensile modulus, lower continuous-use temperature, and higher water-vapour transmission. Relative to polypropylene, PLA has higher stiffness but lower moisture barrier and a narrower heat-seal window. Relative to uncoated cellophane, PLA offers better dimensional stability in humid environments and can be heat-sealed at lower temperatures, but oxygen barrier is generally lower. These differences dictate that PLA film be selected for renewable-origin and compostability requirements rather than for high-barrier or hot-fill performance.

When PLA Shrink Film Replaces PVC or PETG in Low-Temperature Sleeve Applications

Substitution of PVC or PETG sleeves with PLA requires verification of shrink force, solvent seaming, and storage stability. PLA sleeve film has density of 1.24-1.25 g/cm³, close to PETG but lower than PVC; sleeve yields per kilogram therefore differ on a thickness basis. Solvent seaming of PLA sleeves typically uses tetrahydrofuran/cyclohexanone blends or dedicated low-VOC solvents, whereas PETG uses different solvent systems; PLA seam strength can be lower and more sensitive to residual solvent. PLA sleeves perform best at tunnel temperatures below 95 °C; they are not a direct drop-in for high-speed steam tunnels operating above 105 °C because shrinkage force and optical clarity are more temperature-sensitive than PVC or PETG. Storage above 60 % RH can plasticise PLA and shift shrink initiation, so sleeves should remain in barrier packaging until use. For low-temperature beverage and dairy sleeves, PLA provides compostable end-of-life but requires revalidation of tunnel dwell time, air velocity, and nozzle distance.

The following property ranges are representative of uncoated film and should be revalidated against supplier certificates for each grade and thickness.

Compliance Evidence Is Required Before Commercial Use

PLA film must be verified against the following standards for intended use.

Operating boundaries include mandatory pre-drying when ambient storage RH exceeds 60 %, melt temperature not exceeding 230 °C, and avoiding residence time above 10 min to prevent lactide reformation. Additives and colorants must be checked for heavy metals under RoHS Directive 2011/65/EU Annex II when electrical/electronic applications are claimed.