Table of contents
Basic material properties of SAN
Styrene-acrylonitrile copolymer (SAN) is a versatile engineering plastic characterized by its unique material combination of 70-80% styrene and 20-30% acrylonitrile. This composition gives the material exceptional properties that predestine it for demanding technical applications (Liao et al., 2018). The high chemical polarity of the acrylonitrile component significantly influences the morphology of the material and leads to the typical amorphous structures that give SAN its characteristic transparency and uniform mechanical properties.
Characteristic properties:
- High transparency due to amorphous structure
- Excellent chemical resistance to acids and hydrocarbons
- Glass transition temperature between 95°C and 112°C
- E-modulus of approx. 3500-3800 MPa
- Excellent dimensional stability under thermal load
- Limited UV resistance
Crystallinity and structural morphology
SAN is predominantly an amorphous copolymer that has no distinct crystalline structures. This amorphous nature is fundamental to understanding the mechanical properties of the material. In contrast to semi-crystalline polymers SAN does not have a defined melting pointtbut is characterized by its glass transition temperature characterized by its glass transition temperature. The crystallinity has a limited but nevertheless important effect on the mechanical stability of SAN.
The amorphous morphology of standard SAN results in high transparency, excellent dimensional stability and uniform mechanical properties.) If crystalline areas occur due to special copolymer variants or process control, these generally increase the stiffness and hardness, but lead to increased brittleness.
Effects of crystallinity on mechanical properties:
- Crystalline areas increase rigidity, hardness and dimensional stability
- Reduced impact strength and elongation capacity with higher crystallinity
- Amorphous areas ensure better damping and uniform mechanical behavior
- Lower brittleness compared to crystalline plastics
Molecular orientation during processing
Molecular orientation plays a central role in the mechanical properties and processing quality of SAN. Since SAN is a predominantly amorphous polymer SAN is a predominantly amorphous polymer, the macromolecules are partially oriented along the flow direction during injection molding and extrusion technology. This orientation is particularly pronounced in fast processing methods and with thin-walled or elongated components.
The mechanical properties can be increased locally through targeted or process-related molecular orientation. Tensile strength, bending strength and impact strength in particular are positively influenced along the orientation. Oriented macromolecules also ensure better dimensional stability and less material deformation under load, which is of crucial importance for precision parts. The positive effects of molecule orientation include increased mechanical strength and stiffness in the direction of orientation, improved dimensional stability and shape fidelity, uniform surface quality and transparency, and optimized mechanical damping properties.
However, excessive orientation can lead to the development of internal stresses, which can cause stress cracking under chemical stress. This risk is particularly relevant at high processing pressures.
Process parameters for controlling the molecule orientation
To specifically control the molecular orientation of SAN, processing techniques are mainly used that exert targeted flow and shear forces on the polymer chains during shaping (Osnabrück University of Applied Sciences, 2023). The most important method is injection molding, in which the macromolecules are aligned in the direction of flow through high injection speed, increased shear stress and special geometry of the gates.
Temperature control, consisting of mold and melt temperature as well as pressure management, has a strong influence on the degree of orientation. Controlled cooling procedures and temperature-optimized tools enable targeted relaxation of the orientation (JKU Linz, 2016).
Critical process parameters:
- Injection speed and processing pressure
- Ground temperature and mold temperature
- Wall layer thickness and mold geometry
- Cooling rate and tempering regime
- Flow velocity and shear stress
- Extrusion speed for profile production
Process-specific approaches:
- Injection molding: pressure management and gate geometry
- Extrusion: haul-off speed relative to extrusion speed
- Reinforcing additives: glass fibers as orientation aids
Technical applications and material optimization
SAN is used in a wide range of technical applications thanks to its unique combination of properties such as clarity, dimensional stability and chemical resistance. Its resistance to cleaning agents, acids and oils, coupled with its dimensional stability in injection molding and excellent surface appearance, makes SAN a versatile material for demanding applications. Typical applications include laboratory vessels, petri dishes and medical-technical components as well as food and cosmetics packaging. SAN is also used for automotive parts such as interior components and control elements, is used in electronic housings for transparent technical parts and is used in industrial molded parts for office equipment and precision covers.
The variety of grades is mainly due to the different acrylonitrile-styrene ratios as well as special copolymer blends for individual applications. Highly transparent grades with a lower acrylonitrile content are particularly suitable for optical components, while higher acrylonitrile content increases chemical resistance and rigidity.
Conclusion
SAN plastics are a highly interesting material for technical applications due to their amorphous structure and the possibility of targeted molecular orientation. Although crystallinity influences the mechanical properties, it remains limited in standard SAN due to its amorphous nature. The targeted control of molecular orientation through optimized process parameters makes it possible to improve the mechanical properties locally while maintaining the characteristic transparency and chemical resistance.
For users, understanding the relationships between processing parameters, molecular orientation and resulting properties is essential for the successful implementation of demanding projects. The combination of dimensional stability, transparency and chemical resistance makes SAN a reliable solution for injection molding, extrusion and thermoforming in laboratories, medical technology and industrial practice.
List of sources
Osnabrück University of Applied Sciences (2023). Dissertation on plastics processing. Available at:
https://opus.hs-osnabrueck.de/files/6039/kup_9783737611602.pdf
JKU Linz (2016). Polymer technology. Available at:
https://epub.jku.at/obvulihs/download/pdf/1318154?originalFilename=true
Liao, Y. et al. (2018). Synthesis and properties of novel styrene acrylonitrile/polypropylene blends with enhanced toughness. Chemistry Central Journal, 12(1), 78. Available at:
