Introduction and Applications of Polycaprolactone (Part Two)

Because of its excellent biocompatibility, memory, biodegradability, etc., PCL is widely used in various fields. Its products are mainly concentrated in medical and daily use, such as orthotics, sutures, bandages, degradable plastics. And so on, the current methods for preparing these products mainly include injection, blow molding, and extrusion molding [8, 9, 10].

3.1 Injection process

Process route: Drying of raw materials → Feeding → Plasticizing → Injection → Holding pressure → Cooling → Molding → Dressing → Inspection.

Poly(caprolactone) (PCL) polymer materials contain a highly water-absorptive ester-based structure that must be dried prior to processing. Since the softening point of PCL is 60 to 70°C, the drying temperature should preferably be about 50°C. The experimental results show that when the unmodified PCL material is injection molded, the required process temperature is about 120° C., and the process conditions are severe, which brings difficulties in the injection molding (injection molding is generally above 160° C.). If formed in the range of 120-180°C, the memory of the product is significantly reduced. Especially when the temperature is close to the decomposition temperature (200°C), the memory performance of the product is substantially lost. This also shows that it is necessary to modify the PCL.

3.2 Blow molding

Process route: raw material drying → feeding → plasticizing → extrusion → blowing → pulling → coiling → cutting → inspection.

Its process temperature is in the range of 70-120°C, which is basically the same as the extrusion process temperature. Therefore, extrusion molding is the most common method, and most products are obtained by this method.

In the early stage of application of PCL polymer materials, it was a single-layer extrusion product of pure raw materials. Gradually, people recognized its defects, such as low hardness, heavy weight (ρ=1.1g/cm3), high cost, and began to modify it. At present, the process has been changed to two-layer or three-layer co-extrusion. The composite network structure is formed of PCL and high-molecular-weight polymers, and the overall performance of the resulting product is greatly improved.

4. Outlook

As a completely biodegradable material, polycaprolactone is an important way to truly reduce plastic waste, protect ecological balance, and open up new raw materials. It has a huge role in solving the problem of research and development of plastics, white pollution, but at present There are two important issues.

(1) The controllability of degradable plastics, because the controllability mainly depends on the formula, and it is constrained by the environmental differences everywhere, which is the key issue for the development of degradable plastics.

(2) The cost is too high. Although the cost may decrease due to the scale production of biodegradable plastics, in the short term, the cost is still higher than that of general plastics.

Plastic materials are widely used in agriculture, daily necessities industry, and medical care. However, due to the above reasons, environmentally friendly degradable materials, especially fully biodegradable materials, have only a considerable amount in specific areas, such as long-term degradation. Materials sutures, bone nails, long-acting drugs controlled release carriers, if the above problems can be solved, disposable lunch boxes, agricultural film, packaging materials and more medical products may use this polycaprolactone material, of course, "white Pollution can be solved.

In addition, despite the short development time of the shape-memory polymer PCL, it is expected to be used in medical, packaging, construction, automotive, and alarm equipment because of its advantages such as shape memory, light weight, large deformation, and easy shape adjustment. Other areas open up their potential uses. It has been proposed in foreign countries to modify such materials for use in protein or enzyme separation membranes, “chemical engines”, printed materials, recording materials, and optical drive molecular valves [11] and other special fields. However, there are still some deficiencies in the development process:

(1) The shape recovery accuracy is poor.

(2) mechanical properties and chemical resistance to oil, durability, heat resistance and other properties are not ideal.

(3) Processing conditions of shape memory materials are relatively harsh.

In summary, to meet the needs of different applications, the development of varieties with comprehensive performance is the direction of future research.





Author/Mi Hongyu Li Zhenjiang Ma Fengyun Maimaitijiang

(Department of Chemical Engineering, Xinjiang University, Urumqi, Xinjiang, China