The designation Cawiton Bio 3200 identifies a melt-compounded polylactic acid/starch biodegradable 3D printing grade supplied as pellets for extrusion into monofilament and subsequent fused filament fabrication. The compound belongs to the Cawiton Bio product family and comprises a semicrystalline PLA matrix with a destructured starch phase dispersed during compounding. The starch component reduces fossil-derived carbon, lowers melt viscosity relative to neat PLA, and increases moisture sensitivity during storage and processing. Exact formulation and additive composition are supplier-controlled; therefore, the following technical description presents the publicly available performance envelope for this material class unless a lot-specific datasheet value is cited.

Compared with neat PLA 3D printing grades, the 3200 class exhibits a melt-viscosity reduction of approximately 15–25% at 200°C and 100 s⁻¹, which permits printing through 0.4 mm nozzles at lower extrusion torque and reduces filament grinding on ungeared extruders. Tensile modulus is 10–20% lower than neat PLA but higher than PLA/PBAT impact-modified grades. Compared with mineral-filled PLA, the starch phase is less abrasive to brass and hardened-steel nozzles, and the compound has lower density. Compared with PLA/PHA or PLA/PBAT systems, this grade is not a toughened material and should not be selected for living hinges, snap-fit closures, or repeated impact service.

Why Does the Melt Processing Window Require Tighter Control Than Neat PLA?

In industrial filament extrusion of Cawiton Bio 3200, the required melt-temperature band is narrower than that of neat PLA because the starch phase undergoes dehydration and caramelization-type browning above 210°C, while PLA chain scission accelerates when residual moisture exceeds 250 ppm. Pre-drying in a desiccant dryer with supply-air dew point at or below -30°C, hopper temperature 70–80°C, and residence time 4 h is necessary for virgin pellets. Regrind addition above 20% requires the same drying cycle and melt-temperature control within ±5°C to suppress extruder pressure surges.

Production-scale twin-screw extruders with 24:1 to 30:1 L/D, screw speed 150–250 min⁻¹, and die pressure 40–80 bar are typical. The shear-viscosity curve for this class at 210°C falls between 150 Pa·s and 250 Pa·s at 100 s⁻¹, lower than unfilled PLA. Capillary rheometry indicates shear-thinning behaviour with a power-law index of 0.42–0.55 in the shear-rate range 10–500 s⁻¹. The viscosity shift from 190°C to 210°C corresponds to an Arrhenius activation energy of 75–85 kJ/mol. At die shear rates above 600 s⁻¹, sharkskin melt fracture is observed with a 0.4 mm die gap; die land length should therefore be 8–10 times the die gap to reduce entrance extension stress. Molten strand cooling uses a water-bath temperature of 30–40°C with 5–10 mm between die face and water surface, because abrupt quenching below 30°C can generate internal voids from steam flash.

For fused filament fabrication, the feedstock is pre-dried filament rather than pellet. Filament should be stored at or below 30% RH or printed from a heated dry box at 40–50°C. Nozzle temperature of 190–210°C and heated-bed temperature of 45–60°C are used on unenclosed cartesian printers. The first layer is deposited at 200–210°C on a polyetherimide or PLA-compatible adhesion film. Layer height of 0.15–0.25 mm and volumetric speed below 10 mm³/s prevent melt fracture at the nozzle. Higher throughput requires a melt-temperature increase toward 205°C, but operation above 210°C should be avoided for retraction distances over 4 mm because starch-rich deposits can carbonise in the heat break. Fans are used only after the third layer. Layer adhesion in the Z direction is the limiting property in conditioned parts, with published Z-strength values for PLA/starch typically 30–50% of XY tensile strength.

Tensile behaviour and interlayer fracture risk in conditioned prints

Tensile property measurements according to ISO 527-2:2012 on 2.0 mm injection-moulded specimens characterise the compound, but fused-filament parts are anisotropic and usually exhibit lower values than the datasheet. At 100% infill with 0.15 mm layer height and ±45° raster orientation, XY tensile strength is commonly 22–30 MPa, while Z-direction tensile strength is 8–12 MPa. The reduction arises from incomplete chain diffusion across the layer interface and from starch-phase voids at the raster boundary. Flexural modulus measured on printed bars according to ISO 178:2019 is typically 2.5–3.0 GPa with a 0°/90° raster angle. Moisture uptake above 0.8% lowers the glass-transition temperature of the starch-rich phase and reduces flexural modulus by approximately 10–15% after 500 h at 23°C/50% RH.

Biodegradability claims for PLA/starch printing grades are governed by test shape and thickness. Filament or thin-walled prints below the EN 13432 disintegration thickness threshold may degrade in industrial composting at 58 ± 2°C under forced aeration, but dense printed parts with wall thickness above 5 mm do not automatically meet the same certification because oxygen-limited cores disintegrate too slowly. Laboratory aerobic biodegradation is assessed by ISO 14855-1:2012 or ASTM D5338-15; a positive result indicates ultimate biodegradation under controlled conditions, not home-compost or marine behaviour. The grade is not designed for direct food-contact use unless specific migration testing under FDA 21 CFR 175.300 or an equivalent national regulation is completed for the printed article and coloured masterbatch. REACH compliance applies to the formulated compound as supplied; downstream filament manufacturers must re-evaluate SVHC status after adding pigments, adhesion promoters, or impact modifiers.

Incoming quality control on production lines typically checks moisture content by Karl Fischer titration at ≤250 ppm, melt mass-flow rate by ISO 1133-1:2022, and pellet colour against a supplier master standard. If moisture content exceeds 300 ppm, drying time is extended in 30 min increments until the target is reached; over-drying can embrittle the starch phase and reduce filament toughness. Batch-to-batch melt-flow variance of 0.8–1.2 g/10 min is observed when starch-source moisture content varies; this is usually corrected by adjusting barrel zone temperatures rather than screw speed.

The heat-deflection temperature of 50–60°C at 0.45 MPa places the grade outside load-bearing service above 45°C. Printed parts exposed to cyclic humidity show irreversible dimensional change; a printed plaque may exhibit 0.3–0.6% expansion in the XY plane and 0.5–1.0% expansion through thickness after 48 h at 40°C/85% RH. This behaviour is significant in assemblies with metallic inserts or rigid mounting points, because differential expansion can initiate stress cracking at fastener bosses.

If Thin-Wall Parts Are Printed Without Active Cooling, Solidification Rate Limits Feature Resolution

On a moving gantry with a 0.4 mm brass nozzle, extrusion temperature of 195°C, and bed temperature of 50°C, thin-wall details below 1.0 mm require active part cooling after layer deposition. With no cooling fan, the low thermal diffusivity of PLA/starch keeps the layer above the crystallisation onset temperature long enough for edge rounding to occur; measured external corner radii increase from 0.2 mm to 0.5 mm when the fan is disabled. At part-cooling fan duty cycles above 60%, the surface solidifies before the incoming strand can wet the previous layer, producing micro-voids along the raster boundary. This is visible as reduced translucency and lower Z-strength. For unsupported overhangs below 45° from horizontal, a fan duty cycle of 40–60% and a print speed of 30–40 mm/s prevent edge curl without excessive interlayer sacrifice. Published data for this specific configuration is limited; first-article trials on the target printer are required before production lots are accepted.