Лако-красочные материалы — производство

5.9.1

Introduction

For many years, up until the 1930s, natural inorganic or organic substances were the most important raw materials for the production of adhesives. However, with the emergence of polymer chemistry and its rapid development, they were increasingly replaced by synthetic products. In the history of mankind, there is abundant evidence of humans being inspired by the manifold manifestations of efficient bonding in nature. Indeed, bonding as a flexible joining technique was used a very long time ago, and appears to have been one of the most ancient joining techniques utilized by mankind. The most important original raw materials included pitch, bitumen and organic polymers obtained from bones and animal skins, later casein, and last — but not least — starch. The inorganic raw materials used to produce cement will not be discussed here as they have lost significance.

The performance of binders was dramatically improved when adhesives were first manufactured from synthetic raw materials. Over the years, the needs of industry have been increasingly demanding with regards to the strength and long-term durability of adhesives and, in many cases, could no longer be met by natural, raw material-based products. It was at this time when bonding was considered unusable for structural joining purposes. During World War I, for example, the commander of the German Naval Airship Department, Peter Strasser, complained angrily to the Admiralty that the wooden construction used for the Schutte-Lanz ships (the girders of which were made from aspen wood glued with cold-setting casein glues) delaminated in the damp environment ofthe airship hangars in Northern Germany. In fact, such airship girders would still be usable today had they been glued with the presently available phenolic resins used to manufacture plywood (see Chapter 2).

In some fields of application, however, natural material-based adhesives have survived to the present day. Today, approximately 6% of the total adhesives manu­factured in Germany is based on natural raw materials, and this proportion may rise again within the context of economical or ecological aspects. The advantages and disadvantages of natural adhesives are listed in Table 5.10. One of the advantages listed — the avoidance of carbon dioxide discharge — is today much less important as

Table 5.10 Advantages and disadvantages of natural adhesives.

Advantages Disadvantages

<1% of organic raw materials is used worldwide in the manufacture of adhesives. Physiological tolerance, biodegradability — as well as the possibility to break bonds by enzymatic degradation — are all much more important features. It should be noted, however, that enzymatic degradation is very time-intensive and not well-suited to industrial applications in waste management.

One disadvantage of organic polymers is that they are not durable, largely because decomposition and decay serve as efficient recycling systems for natural materials, a fact rarely taken into account when considering their use. It has often been pointed out that the long-term durability of bonds created with natural adhesives is not good but, as will be discussed later, it is possible to improve this situation by adding hardeners that induce crosslinking of the polymer base materials. It may be surprising to find the property ‘economic’ listed as a disadvantage; however, while natural materials may be cheaper than synthetic, their quality may vary depending on the conditions of origin and growth. If such fluctuations occur, and/or the commo­dity price on the world market rises, economic problems may ensue and lead to difficulties in the costing of adhesives.

5.9.2