Twin Screw Extrusion for Thermoplastic Starch Polyolefin Blends
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Solution Overview
Problem
The production of a well-dispersed blend of thermoplastic starch and polyolefin is challenging due to viscosity differences, leading to inhomogeneous blends, especially in large-scale production, where high temperature spots and inadequate screw design exacerbate the issue, resulting in gels and inhomogeneous appearances.
Innovation Solution
A process using two extruders with successive zones, where the thermoplastic starch is produced in a separate extruder with controlled temperature and residence time, and then blended with polyolefin and compatibilizer in another extruder, ensuring homogeneous composition and avoiding high-temperature degassing risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single twin screw extruder is used to produce thermoplastic starch/polyolefin blend, then the process is simple, but the blend becomes inhomogeneous due to viscosity differences and high temperature spots
Solution Approach 1:
The single extrusion process is divided into two separate extrusion units. The first extruder produces thermoplastic starch with controlled gelatinization and degassing, while the second extruder performs the blending with polyolefin. This segmentation allows each extruder to be optimized for its specific function, preventing the viscosity conflicts that cause inhomogeneity in single-extruder systems.
Solution Approach 2:
The thermoplastic starch is prepared in advance in the first extruder, completing gelatinization and degassing before being fed into the second extruder for blending. This preliminary action ensures that the starch is fully gelatinized and degassed before mixing with polyolefin, eliminating the need for high-temperature degassing during blending that would cause inhomogeneity.
2Loss of substance
If degassing is performed at high temperature in the presence of polyolefin, then water removal is effective, but starch decomposition and vapor-related instability occur
Solution Approach 1:
Degassing is performed in advance in the first extruder before the thermoplastic starch is mixed with polyolefin. By removing water content during the starch production phase rather than during blending, the system avoids high-temperature exposure of the starch-polyolefin mixture that would cause decomposition and vapor-related instability.
3Stability of the object's composition
If residence time for thermoplastic starch formation is extended, then gelatinization is complete, but production efficiency decreases
Solution Approach 1:
The process is divided into two parallel production lines, each with optimized residence times. The first extruder is optimized for starch gelatinization with sufficient residence time, while the second extruder performs rapid blending. This segmentation allows each stage to be independently optimized, maintaining gelatinization completeness while improving overall production efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures a homogeneous blend with improved clarity and stability, reducing the risk of decomposition and vapor-related system instability, resulting in a high-quality thermoplastic starch/polyolefin blend suitable for large-scale production.
Implementation Method 1
The ingredients for the formation of the thermoplastic starch as well as polyethylene and compatibilizer are fed into the throat of a twin screw extruder. In the first part of the extruder TPS is formed by the gelatinization process of native starch, glycerol and additives
Implementation Method 2
2c) degassing the thermoplastic starch of step 2b) in the third zone of the second extruder
Implementation Method 3
In the second part of the twin screw extruder the barrel temperature is raised. The PE and the compatibilizer become molten and the TPS phase and the PE phase are mixed intensively into a homogeneous material
Data Source
AI summary
The invention relates to a process for producing a blend of a thermoplastic starch and a polyolefin using a first extruder comprising successive zones comprising a first zone, a second zone, a third zone and a fourth zone and a second extruder comprising successive zones comprising a first zone, a second zone, a third zone and a fourth zone, the process comprising the steps of: 1 a) introducing a polyolefin and a compatibilizer in the first zone of the first extruder, 1 b) melt mixing the polyolefin and the compatibilizer in the second zone of the first extruder, 1 c) adding a thermoplastic starch to the mixture of step 1 b) in the third zone of the first extruder and 1 d) melt-mixing the mixture of step 1 c) in the fourth zone of the first extruder to obtain the blend, wherein the thermoplastic starch is produced in the second extruder by a process comprising the steps of: 2a) introducing starch in the first zone of the second extruder, 2b) adding a plasticiser to the mixture of step 2a) in the second zone of the second extruder to obtain the thermoplastic starch, 2c) degassing the thermoplastic starch of step 2b) in the third zone of the second extruder and 2d) pressurizing the degassed thermoplastic starch of step 2c) in the fourth zone of the second extruder to be moved to the third zone of the first extruder.