The memory effect of plastics: The basis of modern shrink products
Shrink products such as shrink tubing, shrink sleeves, and shrink collars are indispensable tools in technology and industry. Their strength: Thanks to the memory effect, they automatically adapt to almost any component geometry when heated, fit perfectly, and ensure lasting protection under a wide range of operating conditions. Learn how the memory effect works, what role radiation crosslinking plays in this process, and in which industries this technology is used most frequently.
The “superpower” of shrink products
The special feature of shrink products is their controlled return to a defined shape. The material “remembers” its original state and contracts automatically when heated – this behavior is called shape memory or memory effect. Behind this seemingly “magical” property lies a physical material phenomenon: certain plastics store their original shape and return to it when thermally activated.
As a result, shrink products adapt permanently and form-fittingly to the respective component, sit firmly in place, and seal reliably. This results in clear advantages in terms of tightness and protective effect, high ease of installation, and thermal and mechanical resilience. Shrink products are used in electrical engineering, electronics, telecommunications, mechanical engineering, and many other industries.
Why shrink products are indispensable in technology and industry
Shrink products fulfill key protective and insulating functions in technical systems. They are used wherever wires, cables, pipes, or connections need to be reliably protected.
Typical functions of shrink products:
- Electrical insulation: Protection of conductors, cable connections, and solder joints
- Mechanical protection: Protection against abrasion, tensile stress, and vibrations
- Environmental and weather protection: Sealing against moisture, chemicals, corrosion, and dust
- Repair and re-insulation: Restoration of damaged insulation
How does the memory effect work of plastics?
The memory effect describes a plastic’s ability to return to its originally stored shape after targeted deformation when reheated. This effect forms the functional basis of shrink products and only occurs when certain structural requirements are met in the material.
How the memory effect works
- First, the plastic is heated until its polymer chains can move sufficiently.
- In this state, the material is mechanically deformed in a controlled manner (e.g. expanded).
- This new, temporary shape is then fixed by subsequent cooling.
- If the material is reheated later, the polymer chains become mobile again.
- The restoring forces stored in the material are activated.
- The component finally returns to its original shape.
This behavior is typical for shape memory polymers. The decisive factor here is not the material class, but the internal structure of the polymer.
Heating and the memory effect becomes visible
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More InformationWhy not every thermoplastic is suitable for shrink applications
The memory effect in thermoplastics: Non-crosslinked thermoplastics have very low elastic recovery properties. Their polymer chains are not crosslinked and can move freely against each other when heated.
Due to the lack of crosslinking in the amorphous areas, there is no molecular “net” that pulls the chains back into their original shape. When an non-crosslinked thermoplastic is heated, it becomes soft and malleable, but it only retracts independently to a very limited extent and with little force, as the crosslinked amorphous areas of the semi-crystalline thermoplastic are missing.
The memory effect is therefore only very slight in non-crosslinked thermoplastics and is therefore insufficient for technical shrink applications.
Differentiation from other polymer classes
Although the memory effect is often mentioned in connection with polymers, not all polymer classes are suitable for reproducible deformation. In addition to non-crosslinked thermoplastics, thermosets and elastomers in particular are also considered unsuitable:
- Duroplasts: They have a highly crosslinked polymer network and are no longer thermally deformable. A reproducible memory effect is therefore not possible.
- Elastomers: These materials also possess elastic properties, but cannot be specifically returned to a predetermined shape by controlling the temperature. At too high temperatures, they lose their elasticity and plastic deformation occurs. Thermally programmed deformation is therefore not possible with them.
Radiation crosslinking as the key to the memory effect
In order for a thermoplastic to exhibit a pronounced memory effect, radiation crosslinking must be applied beforehand. In semi-crystalline thermoplastics, radiation is used to specifically crosslink the amorphous areas. This network stores the original shape of the material.
- When heated above the crystallite melting temperature, the material becomes malleable.
- In this state, the existing polymer network is stretched in the crosslinked amorphous regions.
- Upon subsequent cooling, the crystalline regions harden and fix the changed shape under tension.
- If the material is heated again, the crystalline components melt once more, and the network in the amorphous regions contracts back to its original shape.
The crosslinked polymer network activates stored restoring forces, allowing the material to reliably return to its original shape. The interaction between crosslinking and reversible crystal structure generates the reproducible restoring force – the fundamental basis of the memory effect in shrink products.
What are the advantages of the memory effect?
The memory effect is the functional basis for the performance of heat-shrink tubing, heat-shrink sleeves, and heat-shrink collars.
The most important advantages for heat-shrink applications include:
- Permanent dimensional stability
- Reproducible shrinkage and recovery behavior
- Reliable sealing and protective effect
- Ease of installation and tolerance compensation
- Increased thermal and mechanical resilience
- Detachable connections
These properties result in higher quality and longer service life and are decisive for the use of heat-shrinkable products in a wide range of industries.
Where heat-shrinkable products with memory effect are used
Heat-shrinkable products are used wherever dimensional stability, reliable insulation, tightness, and mechanical stability are required over long periods of time.
Depending on the industry, the focus is on different requirements such as thermal resilience, ease of installation, or protection against environmental influences.
Electrical & Electronics
In electrical and electronics, heat-shrink products provide permanent electrical insulation, reliable protection against moisture and dust, and stable mechanical strain relief for connections, even under thermal stress.
Typical applications:
- Heat-shrink tubing for electrical insulation of wires and contacts
- Insulation of solder joints
- Strain relief
- Protective covers for cables, connectors, and assemblies
- Sheathing for cable and wire systems
- Connection technology
Automotive & E-mobility
In the automotive and e-mobility environment, heat-shrink products are exposed to high thermal and mechanical stresses. Thanks to their memory effect, they enable easy-to-install solutions with permanent dimensional stability, even in complex installation situations.
Typical applications:
- Heat-shrink tubing for cable harnesses
- Protection and sealing solutions for plug and connection elements
- Sheathing in areas subject to thermal and mechanical stress (e.g., drive, on-board power supply)
- Cable routing systems
Infrastructure & Building Technology
In infrastructure and building technology applications, the focus is on long-term protection against moisture, corrosion, and environmental influences. Heat-shrinkable products offer reliable sealing and long-term stability in these areas.
Typical applications:
- Heat-shrink sleeves for cable and pipe connections
- Heat-shrink collars for sealing transitions
- Protection solutions for cables in energy, heating, and supply networks
Mechanical engineering
In mechanical engineering, heat-shrink products are used to protect components and cables from abrasion, corrosion, and mechanical stress. Thanks to the memory effect, the plastics adapt flexibly to different component geometries and remain permanently dimensionally stable.
Typical applications:
- Abrasion and corrosion protection
- Marking of cables
- Shrink sleeves for protecting moving or exposed components
- Sealing and protection solutions for industrial components
Conclusion: Radiation crosslinking as the basis for reliable shape memory polymers
The memory effect in plastics is much more than a physical phenomenon. It is the functional basis for high-performance shrink products. It is what makes form-fitting hold, reliable tightness, high resilience, and lasting mechanical stability possible.
Radiation crosslinking specifically influences the internal structure of the thermoplastic, thus creating the conditions for controlled, reproducible shape memory. This makes crosslinked thermoplastics high-performance materials for reliable, durable, and easy-to-install shrink solutions in numerous industries.
“Regardless of the industry, shrink products must be permanently tight, dimensionally stable, and resilient. Radiation crosslinking creates the conditions for the safe use of shrink tubing, shrink sleeves, and shrink collars in a wide variety of industrial applications.”