For converters evaluating compostable blown film feedstocks, the designation Bio-polyolefins 3015 Starch-Based Blown Film Compostable Grade identifies a starch-based thermoplastic compound intended for tubular film extrusion, not a petrochemical polyolefin. The suffix 3015 functions as the manufacturer’s grade identifier within the Bio-polyolefins portfolio. Although the trade name contains the term “polyolefins,” published technical positioning data indicate that the product falls into the thermoplastic starch/compostable copolyester blown film class rather than a polyethylene or polypropylene chemical family. Product-specific numerical values are limited in independent literature; consequently, the quantitative ranges in this document refer to the class envelope for starch-based blown film compostable grades unless a supplier certificate of analysis is explicitly cited. The grade’s primary application window is industrially compostable film such as organic-waste liners, produce bags, and short shelf-life shopping bags tested under EN 13432 or ASTM D6400.

What separates 3015 from fossil polyolefins in blown film conversion?

A starch-based blown film grade differs from a petrochemical linear low-density polyethylene in density, melt elasticity, and water-vapour transmission. Class-typical density for starch-based blown film compounds ranges from 1.20 g/cm³ to 1.30 g/cm³ under ISO 1183-1, whereas LLDPE film resins are typically 0.918 g/cm³ to 0.925 g/cm³. The higher density reduces film yield per kilogram and changes bending stiffness at equal gauge. Melt elasticity is lower than LLDPE, so the bubble is less tolerant of blow-up ratios above 3.5:1 and sudden frost-line movement. Water-vapour transmission for starch-based blown film at 25 µm is frequently 150 g·m⁻²·24 h⁻¹ to 300 g·m⁻²·24 h⁻¹ when measured by ISO 15106-2 at 38 °C and 90% RH; the same gauge of LLDPE typically transmits below 5 g·m⁻²·24 h⁻¹. This makes the product suitable for respiring produce or organic-waste liners but unsuitable for high-moisture barrier packaging without lamination or coating.

Extrusion screening trials on starch-based grades frequently expose four bottlenecks that do not appear with polyolefins. First, pre-drying is mandatory because absorbed moisture above 0.3 wt% generates steam at the die lip, producing pinholes and bubble chatter. Second, the melt-temperature window between plastication and starch degradation is narrow; a melt probe reading above 165 °C is often associated with viscosity loss, discolouration, and acrid odour, while below 145 °C the starch phase may remain partially unplasticized and create fisheyes. Third, purging from the extruder cannot be performed with high-temperature engineering resins because the starch phase decomposes and carbonizes; a low-MFR LDPE purge or a starch-compatible purge compound is preferred to avoid cross-contamination. Fourth, moisture regain in the feed throat at relative humidity above 60% re-wets dried granules within 20–30 min unless a hopper dryer with a supply-air dew point of -30 °C or lower is used and the surge hopper is sealed. These constraints have been observed on production-scale single-screw extruders with L/D ratios of 25:1 to 30:1.

Material constitution and the melt-degradation window

Prior to extrusion, the granulate should be consolidated in a sealed, moisture-proof package. The starch phase in this class is plasticized by a polyol system, typically glycerol- or sorbitol-containing, and is compounded with a biodegradable copolyester such as PBAT or a polybutylene succinate-based phase to raise tear strength and seal integrity. The exact formulation ratio is proprietary and should be confirmed from the supplier safety data sheet and certificate of analysis. In melt processing, the copolyester phase contributes higher elongation and melt flexibility; the starch phase contributes stiffness, biobased carbon content, and rapid compost disintegration. The thermal degradation boundary is time-temperature dependent: residence times above 8 min at 160 °C may induce chain scission in the copolyester phase and Maillard-type discolouration in the starch fraction. Published data for this specific configuration are limited; the 8 min threshold should be treated as a safe house limit derived from class-level degradation studies rather than a product-specific kinetic constant.

Rheologically, the melt is shear-thinning but exhibits lower elongational viscosity than LLDPE, so the bubble cannot sustain deep draw-down. Capillary rheometry scans at 150 °C for starch-based blown film grades generally show apparent shear viscosity from 200 Pa·s to 900 Pa·s at 100 s⁻¹, whereas LLDPE can be higher and more stable across the same shear range. The practical result is that die pressure remains manageable, but bubble tension must be kept low. Internal bubble cooling is possible but should be used with pressure-balance control to avoid condensation; external cooling is preferred for gauges below 25 µm because moisture-laden internal air can disrupt frost-line formation.

The following table is not a certificate of analysis; it reports class-typical ranges for starch-based blown film compostable grades and is included to support early feasibility work.

In municipal organic-waste collection, film is converted into bags with a thickness between 20 µm and 50 µm. The compostability requirement is not limited to aerobic biodegradation; it includes disintegration, absence of harmful residues, and packaging recovery compatibility. Because the class to which 3015 belongs has a starch-rich phase, disintegration under ISO 16929 pilot-scale composting is generally faster than for PBAT-rich or PLA-rich films, but mechanical strength at equal gauge is lower. This trade-off must be evaluated using downstream sealing and collection conditions. For high-moisture organic applications, the grade may require a higher gauge than LLDPE to compensate for lower puncture resistance and stiffness. Seal initiation is generally lower than for LLDPE; sealing jaws should be set initially to 110 °C to 130 °C, but the supplier datasheet should be used to fix the final profile.

When relative humidity exceeds 60%, drying and feeding constraints change

Drying is not optional for the starch phase. A desiccant-bed dryer with a supply-air dew point of -30 °C to -40 °C and an air temperature of 60 °C to 70 °C is common for starch-based blown film grades. Drying time of 4 h is class-typical for granules stored inside a sealed original package; if the original package was opened at high relative humidity, drying may require 6 h to 8 h. Target residual moisture below 0.3 wt% should be confirmed by a moisture analyzer rather than assumed from drying time. If the hopper exceeds 70 °C, the polyol plasticizer may migrate to the granule surface and cause feed-throat slip; if the hopper is below 50 °C, the required moisture removal may not be complete. This is an operational boundary, not a universal set point. A 45 mm extruder with L/D 30:1 and a grooved feed section will require a lower screw speed than a smooth-bore 60 mm machine because starch-rich compounds generate high friction and pressure override at high throughput. Screw speeds from 25 rpm to 60 rpm are generally used on 45 mm lines, but the exact curve should be derived from torque and melt-pressure limits.

Extrusion processing of starch-based blown film grades is constrained by a critical melt-temperature threshold of approximately ±5 °C because the distance between complete plastication and degradation is narrow. Thermocouple readings alone can mislead; an infrared melt-temperature probe placed in the adapter is more indicative because wall shear heating can locally exceed the set temperature. A melt-temperature gradient of 5 °C to 10 °C across the screw profile is typical, with feed zone 130 °C, compression zone 145 °C, metering zone 155 °C, adapter 155 °C, and die 150 °C as class-level starting points. The die gap should be 1.0 mm to 1.4 mm; a gap below 0.8 mm increases melt shear and local temperature, while a gap above 1.6 mm reduces back pressure and can produce gauge bands. Bubble geometry is maintained at a blow-up ratio of 2.0:1 to 3.0:1. A BUR of 3.5:1 is possible only with high-molecular-weight copolyester modification and external cooling; above that, bubble tear at the frost line is commonly observed. Frost-line height should be 1.0 to 2.5 die diameters; lowering the frost line below 1.0 die diameter may trap moisture at the nip and cause blocking.

Downstream conversion of the extruded film is sensitive to the difference between starch-based compostable film and PE. In bag-making, the film exhibits lower hot-tack strength than LDPE at equivalent seal-bar temperatures, and the seal-strength plateau occurs over a narrower temperature band. On rotary sealing machines, the initial sealing window can be as narrow as 10 °C; an increase from 120 °C to 135 °C may take the seal from weak peel to burn-through if dwell time is too long. Corona treatment at 38 mN/m to 42 mN/m is often required for print adhesion; the level decays more rapidly in humid storage than on LDPE. Slitting and winding must use lower tension because the film is less stiff and can develop core blocking at high winding pressure. These are class-level operational data; product-specific seal-strength curves and treatment-decay data should be obtained from the supplier’s technical datasheet.

Compared with PBAT-rich compostable film, a starch-rich grade of this type tends to exhibit higher tensile modulus, lower tear resistance, and higher water-vapour transmission. Compared with PLA-rich film, the material tends to produce softer hand feel and more rapid disintegration, but it also exhibits greater moisture sensitivity and lower gloss. This is not a defect but a formulation-specific profile. The product should therefore not be substituted into a PBAT or PLA film specification without re-qualifying seal strength, bag drop performance, and printing adhesion.

Additive compatibility differs from polyolefins. Amine-based slip or antistatic additives should not be blended into the melt because residual basic moieties can catalyze hydrolysis of the biodegradable copolyester phase during extrusion and later humid storage. Hydrocarbon waxes used in PP or PE are not effective dispersants for the starch phase; polar ester-based external lubricants should be used if die-lip buildup is observed. The material should not be dry-blended with conventional polyolefin regrind because compostability certification, density, and melt-flow relationships are all disrupted. Machinery cleaning requirements are strict: polyolefin residues in the screw or die can produce incompatible domains and reduce bubble integrity. Conversely, starch-based residues left in a polyolefin line cannot be purged by temperature alone; the screw and barrel should be mechanically cleaned if a dedicated starch line is not available.