Research and Application of Shape Memory Polymers

Research and Application of Shape Memory Polymer Materials Hu Jinlian, Yang Zhuohong (Technical Department, Department of Textiles and Clothing, Hong Kong Polytechnic University, Hong Kong Kowloon Red). This article reviews the progress of research on shape memory polymers, such as polyurethane, cross-linked polyethylene, poly- and trans-polyisoprene, analyzes the shape memory mechanism of polymer materials, and introduces shape-memory polymer materials. The application in textiles, and look forward to its application prospects.

1 Rumors Since the 1960s, shape memory materials have attracted a great deal of interest due to their unique properties. Shape memory materials can be stimulated by thermal, chemical, mechanical, optical, magnetic, or electrical stimulation to respond to changes in the material's technical parameters such as shape, position, strain, hardness, frequency, friction, and dynamic or static characteristics. . Because shape memory materials have excellent properties, such as shape memory effect, high recovery deformation, good shock resistance and adaptability, as well as being easily combined with other materials in the form of wires, particles or fibers to form a composite material, etc. More attention has been paid to 12. Shape memory polymer or shape memory polymer (SMP, Shape Memory Polymer) as a functional polymer material is a new branch of research, development and application of polymer materials, and due to the shape memory polymer Textile materials are compatible and have potential application advantages in textiles, clothing and medical care products. 13. This paper reviews the research progress of thermally induced shape memory polymer materials and their application prospects in textiles.

2 Shape memory mechanism and its process The shape memory process of a polymer can be simply expressed as 4:/shape variables; tg—polymer glass temperature; tms—polymer soft segment melting temperature.

The mechanism of action can also be explained by the molecular model: Health Supervisor; Yang Zhuohong, male, Ph.D. at the Hong Kong Polytechnic University. For shape memory effect, Professor langer of the Massachusetts Institute of Technology graphically expressed changes in the shape of polymer materials. The shape memory polymer reverts to its original form within 45 seconds at a temperature of 65C.

It is generally accepted that such shape memory polymers can be considered as a two-phase structure, ie, a stationary phase (or hard segment) that maintains a fixed shape during shape memory and a reversible phase that reversibly cures and softens with temperature change. (or soft segment). The reversible phase is generally a physical cross-linked structure and is usually represented in the shape memory process as a soft segmented shape memory polymer material and the reversible conversion of the crystalline, glassy and molten states is used; the stationary phase includes a physical cross-linked structure or Chemical crosslinked structure. In the process of shape memory, its aggregation state structure remains unchanged, which is generally glassy, ​​crystalline, or a mixture of both. Therefore, the shape memory mechanism of this type of polymer can be explained as follows: When the temperature rises to the melting point or high elasticity of the soft segment, the microscopic Brownian motion of the soft segment is intensified and the deformation is easy to occur, but the hard segment is still in the glassy state. Or the crystalline state prevents the molecular chain from slipping, resists deformation, and applies external forces to set the shape; when the temperature is reduced to the glassy state of the soft segment, the deformation is frozen and fixed, and the temperature is increased to return to its original shape. It can also be considered that shape-memory macromolecules exhibit high elasticity at the melting point of the soft segment of the polymer, and artificially introduce factors such as temperature drop or rise in the process of high-elasticity changes, and high-molecular materials occur from high levels. Process of transition from the elastic state to the glass state 16. 3 Shape memory polymer materials 3.1 Polyurethane shape memory Polyurethane is currently the most widely studied and specific type of shape memory polymer material. These polymers have good biocompatibility and mechanical properties. By adjusting the composition and ratio of the components, materials with different transition temperatures can be obtained. Polyurethane is usually made of polyisocyanate, polyether or polycool, and chain extender, but the shape memory poly ammonia has certain requirements for its raw material components: soft segment and hard segment. The phase separation must be sufficient and the higher the phase separation, the better the shape memory characteristics.

The hard segment content is appropriate and can serve as a cross-linking point.

The soft segment should have a certain degree of crystallinity. Polyether or polycondensed molecular chains used should be as regular as possible and have a molecular weight of at least 2000 or more.

The study of shape memory polyhydrazine can be traced back to the late 1980s. Later, in the early 90s, Hayashi developed 781, a 25-residue Polyurethane Cool Variety, and applied for a series of patents. 910. On this basis, Mitsubishi Heavy Industries of Japan successfully developed a class of polyurethanes with shape memory function. Diplex is widely used in apparel, medical, aerospace, chemical, industrial materials, information technology, and food and cosmetic makeup industries. 1111. Korean Byurg et al. , Aromatic diisocyanate is a hard segment of a small molecular chain diol, which is used to synthesize shape-memory polyurethane, and studies the effects of soft segment molecular weight and soft segment content on the cool-memory properties of shape memory polycondensation 12141. , Researchers at the China University of Science and Technology have used a solution polymerization method to synthesize linear polyblocks with shape memory functions, and studied the crystallinity and microphase separation behavior of the system. 151. In recent years, the task force has also A systematic and systematic study of the synthesis, structure and properties of polymembrane in shape-memory was conducted. For the first time, a cross-linking agent was introduced into the molecular design to obtain moderately cross-linked shape memory polyamines. Cool. In addition, the shape memory poly ammonia cool as a textile material, in the application of textile research and exploration 16181. 3.2 cross-linked polyethylene According to reports, cross-linked polyethylene is the earliest practical application of shape memory polymer materials. Through physical cross-linking or chemical cross-linking methods, the appropriate degree of crystallinity and degree of cross-linking are controlled so that the macromolecular chains crosslink into a network structure as a stationary phase, and the formation and melting of crystals are used as a reversible phase to obtain a shape memory effect. The cross-linked polyethylene has a response temperature of about 110 to 130C. The cross-linked polyethylene has significant improvements in heat resistance, mechanical properties and physical properties, and due to cross-linking, the intermolecular bonding force increases to impede the crystallization, thereby increasing the room-temperature shrinkage resistance of polyethylene and Transparency 19211. 3.3 Polyester Polycool is a type of polymer containing a carbonyl radical bond on the macromolecular backbone. Shape memory functions can also be obtained by peroxide crosslinking or radiation crosslinking. By adjusting the proportion of polymer carboxylic acid and polyol components, shape memory polycondensation with different response temperatures can also be produced. They have good weather resistance, heat resistance, oil resistance, and chemical resistance, but the hot water resistance is not very good. Polyhydrazine terephthalate, polyhexacol, and polylactic acid, etc., are currently used in the research of polyhydrazine polyhydrazines. 2224. Trans-1,4-polyisoprene has not been cross-linked. Diene is a crystalline thermoplastic polymer with no shape memory effect. However, trans-polyisoprene molecular chains contain a double bond structure that allows them to complex and cure like natural rubber. Trans-polyisoprene having a chemically cross-linked structure obtained by crosslinking with sulfur or peroxide exhibits a pronounced shape memory effect. The shape memory effect and recovery temperature can be adjusted by the ratio, degree of vulcanization, and additives. Such trans-polyisoprene has the characteristics of rapid deformation, large restoring force, and high recovery accuracy, but the heat resistance and weather resistance are poor. 2526. 3.5 Other polymers with shape memory effect reported so far are still poly. Ethylene Oxide copolymer, polynorbornene i271, styrene-butadiene copolymer 28, polyvinyl chloride 29, and the like.

(4) Compared with shape memory alloys, shape memory polymers have been used in textiles for a long time. However, due to their light weight, large deformation, and ease of forming and shaping, shape memory polymers have not been studied for a long time. And the shape recovery temperature is easy to adjust and other advantages, has been widely used in medical equipment, packaging materials and automotive fields 30341. Their application in textile and clothing, can be spinning to give the yarn memory function (such as Japan developed poly ammonia Cool Polyester Diaplex) can also be used as a fabric coating agent for functional coating to shape memory fabrics. Specifically, the current application mainly has the following two aspects, and most of its materials are focused on shape memory poly ammonia.

41 Application in waterproof and breathable fabrics The use of shape-memory polyurethane foams can be temperature controlled. The air permeability is significantly changed around the response temperature range. When the response temperature is set at room temperature, the coated fabric is coated. Can play a low-breathable warm-keeping effect at low temperatures (below the response temperature), and high-air-permeable heat dissipation at high temperatures (higher than the response temperature). Because the pore size of the film is much smaller than the average diameter of the water droplets, it can provide a waterproof effect, so that the fabric can maintain good wearing comfort under various temperature conditions.

According to Sakamoto Mitsubishi Heavy Industries Co., Ltd., Azekum, a shape-memory polyurethane wet-coating fabric, not only can be waterproof and breathable, but also its air permeability can be controlled by body temperature to achieve the effect of regulating body temperature. The mechanism of action is that the molecular gap of the polyurethanes expands or shrinks as the body temperature rises or falls. Just like human skin, it can open or close the pores according to the body temperature and play a role in regulating the temperature and keeping the warmth, thereby improving the fabric pair. Applicability of the environment and comfort of wearing 3537. 42 Application in crease-prevention finishing Using the shape memory recovery function of polymers, garments made of such fabric yarns or fabrics that have been shape-memorized have a different meaning than traditional ones. Anti-wrinkle function. When such garments have a sufficiently strong shape memory function, the wrinkles formed at a normal temperature of the garment can be eliminated by warming to restore the original shape.

Even we can design the response temperature at room temperature or body temperature range, so that the formed wrinkles can be eliminated instantly.

Sakamoto Kobayashi and Kayash have reported that the use of shape memory polymer powder coating the fabric finishing, the fabric can be restored at room temperature or high temperature wrinkle marks, has a good shape memory effect 110. 4.3 The work of the task group In recent years, the research group has conducted research on shape memory polymer materials and their application in textiles, and has received funding from the Hong Kong Research and Development Bureau and the Hong Kong industrial community. Relying on project funding, we have conducted in-depth and systematic research on the application of shape memory materials in textiles, and proposed the following working flow chart for the entire project: 5 Outlook Shape Memory Polymer Compared with Shape Memory Alloys and Shape Memory Ceramics , With a large memory effect, low response temperature, low cost, easy processing and forming a wide range of adaptation and other characteristics, but there are still many deficiencies, such as small deformation recovery, poor heat resistance and low recovery accuracy. Therefore, in the molecular design of the shape memory polymer and the research of the composite material, etc., it has yet to be further studied, and the work in application development also has great potential to be tapped.

With the further development of the mortar, the performance of the shape memory polymer will continue to increase, and the cost will continue to decrease. As a new type of functional polymer material, shape memory polymers will be more widely used in the fields of textiles, clothing and daily necessities, and obtain good economic and social benefits. iXH