Alginate-based biodegradable films with co-rotating twin screw extrusion

Alginate-based biodegradable films with co-rotating twin-screw extrusion — Application note (Thermo Fisher Scientific)

Significance of the topic

Reducing single-use plastic waste is a major global challenge. Biodegradable films made from biopolymers such as alginate offer reduced environmental footprint and potential for renewable sourcing. Moving film production from slow, batch casting to continuous extrusion can accelerate formulation screening, improve process scalability, and enable more consistent film quality for applications in food packaging, biomedical materials and other disposable products.

Objectives and study overview

This application note demonstrates the use of a co-rotating twin-screw extruder (Thermo Scientific Process 11) to produce alginate-based films by hot-melt extrusion. The work aims to (1) present a process configuration and operating window for alginate films, (2) illustrate sample preparation and mechanical testing, and (3) highlight process-related observations useful for further development (including guidelines for die heating, feeding, mixing and take-off mechanics).

Methodology and process

The formulation used natrium alginate and a water–glycerol plasticizer (glycerol 50 wt% of the liquid mixture), yielding approximately 32.6 wt% glycerol in the final extrudate. Feeding and throughput: gravimetric dry-feed of alginate at 160 g/h and peristaltic dosing of the water–glycerol mixture at 300 g/h introduced in a downstream feed zone. The twin-screw system used mixing and kneading elements to disperse the liquid into the polymer. Key processing settings reported:

• Extruder speed: 400 rpm.
• Barrel temperatures: Tbarrel2 = 80 °C, Tbarrel3 = 80 °C, Tbarrel4–8 = 110 °C.
• Die adapter temperature: 110 °C; slit die electrically heated to 100 °C; slit die dimensions: 30 mm width, gap set to 1 mm.
• Film take-off: sheet take-off apparatus with controlled draw over three cooling rolls to ensure uniform thickness.

The extruded sheet was conditioned and samples were cut oriented both parallel (0°) and perpendicular (90°) to the extrusion direction for mechanical testing. Sample geometry: 9 mm width, 0.7 mm thickness, 20 mm gauge length.

Mechanical testing

Uniaxial quasi-static tensile tests were performed on a HAAKE MARS iQ Air Rheometer (TM-CR-O450) using a DMTA-style solid clamp fixture. Test parameters included a constant crosshead speed of 0.1 mm/s, temperature controlled at 25 °C, data acquisition at 1000 points per test, sandpaper on clamps to prevent slippage and video capture of rupture events. Each sample was tested at least in triplicate.

Used instrumentation

• Thermo Scientific Process 11 co-rotating twin-screw extruder.
• Gravimetric feeder for alginate powder.
• Peristaltic pump for water–glycerol dosing.
• 30 mm adjustable-gap slit die (electrically heated).
• Sheet take-off apparatus and three-roll cooling system.
• Thermo Scientific HAAKE MARS iQ Air Rheometer (TM-CR-O450) with DMTA solid-clamp setup.
• Camera for rupture capture and sandpaper-backed clamps to avoid slippage.

Main results and discussion

The extruded alginate films displayed anisotropic mechanical behavior: samples pulled perpendicular to the extrusion direction were more flexible and exhibited higher elongation before break compared with samples aligned with the extrusion direction. Tensile stress–strain curves showed clear dependence of maximum stress and strain at break on pulling direction, reflecting orientation introduced during extrusion and cooling. The data indicate that mechanical properties can be tuned by formulation (plasticizer fraction and solids content) and by process parameters (mixing, draw speed, die gap and temperature). Operational observations included the usefulness of die heating (to ~100–110 °C) to prevent blockage and the need for sufficient film toughness to accommodate drawing and roll handling without tearing.

Benefits and practical applications

• Continuous twin-screw extrusion enables faster formulation screening and higher throughput than casting methods, reducing development time and cost.
• Process modularity (mixing zones, heated die, adjustable gap) allows tailoring of film thickness and homogeneity for packaging or specialty films.
• Alginate films are attractive for food-contact and biomedical uses due to biocompatibility and biodegradability; mechanical tuning via plasticizers broadens application potential.

Future trends and opportunities

• Transitioning from cast to blown-film extrusion or optimizing cast-film drawing for thinner, oriented films suitable for flexible packaging.
• Exploring alternative plasticizers, crosslinking strategies (e.g., ionic crosslinking with divalent cations) and composite formulations (proteins, fibers, antimicrobial agents) to improve strength, barrier properties and functionality.
• Implementing inline process analytics (rheology, moisture sensors, thickness gauges) for real-time control and scale-up.
• Assessing biodegradation, compostability and life-cycle impacts to support regulatory and commercial adoption.

Conclusions

Co-rotating twin-screw extrusion is a viable route to produce alginate-based biodegradable films with controllable mechanical properties. The reported process parameters (feed strategy, temperature profile, die heating and take-off) and tensile testing protocol provide a practical starting point for formulation development. Observed anisotropy highlights the importance of process-induced orientation when designing films for specific mechanical demands. Continuous extrusion offers a scalable alternative to casting, enabling faster development and potential industrial application in sustainable packaging and related fields.

References

1. Jha A., Kumar A. Biobased technologies for the efficient extraction of biopolymers from waste biomass. Bioprocess and Biosystems Engineering. 2019;42:1893–1901.
2. Mellinas C., Ramos M., Jiménez A., Garrigós M.C. Recent trends in the use of pectin from agro-waste residues as a natural-based biopolymer for food packaging applications. Materials. 2020;13:673.
3. Gonçalves de Oliveira J. et al. Active food packaging: Alginate films with cottonseed protein hydrolysates. Food Hydrocolloids. 2019;92:267–275.