Khác với hầu hết các loại cao su tổng hợp, vật liệu đàn hồi PU bị thủy phân ở những mức độ nhất định. Phần tài liệu sau sẽ so sánh tính kháng thủy phân của các loại vật liệu đàn hồi PU khác nhau và các cách hiệu quả để cải thiện tính chất này.

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With most commercial elastomers the property of hydrolytic stability is not even quoted in data on their properties and they are regarded as possessing excellent resistance to aqueous environments due to their chemical structure being based on all carbon-carbon linked atoms. With polyurethane elastomers, however, the presence of -COC- and -COOC- groups in the main-chain structure results in these materials inevitably undergoing some degree of hydrolytic attack in the course of time. It is primarily the rate of this attack which is considered (it is assumed to occur in principle) as this varies over a very wide range, being dependent upon the chemical structure of the polyurethane. Hence one of the properties most frequently quoted when considering the limitations of polyurethanes is their susceptibility to hydrolytic attack.

It is possible to make some general comments on the relative hydrolytic stability of different polyurethane elastomer structures. The three principal linear polyol series used in synthesizing urethane elastomers can, for hydrolytic stability, be ranked in the following order:

polyether > polycaprolactone > polyester

(highest stability → lowest stability)

Other useful points are:

1. Amine cured polycaprolactones, stabilized with a carbodiimide, have similar resistance to polyethers.

2. Sulphur-cured urethane elastomers have the least resistance to hydrolysis (possibly the typical amine-based sulphur-accelerator combination used accelerates hydrolysis) (see Table 13.5).

3. Carbodiimides (e.g. Staboxal PCD by Bayer) are effective in stabilizing all polyester urethanes against hydrolytic attack; they are not effective when used with polyether-based urethane elastomers.

4. In general it is true that the longer the hydrocarbon chain of the glycol portion of a polyglycol adipate the more resistant is the polyester to hydrolysis.

5. Fungus attack of polyurethanes, especially at relatively low ageing temperatures (15-30°C) occurs as a generalization. The incorporation of a fungicide is effective in preventing this effect.

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Trích đăng từ sách Polyurethane Elastomers, C. Hepburn, Elsevier Science Publisher, 1992, trang 380 – 382

(vtp-vlab-caosuviet)