21 ноября, 2015 
Pokraskin Historically, and up to the early 20th century, aqueous natural glues were used for bonding wood (see Section 5.9). For structural purposes, animal glues were preferred to plant glues as they generally produced higher strengths in the bond-line. Animal glues are composed of proteins that are responsible for both adherence (adhesion) and strength (cohesion). They are applied in a hot or warm condition and, owing to jellification during cooling, a high early strength is achieved. The glue film is produced by the evaporation of water, resulting in an elastic bond-line that swells or shrinks with changing ambient moisture, similar to wood.
When synthetic adhesives were developed in the mid-20th century, the use of natural glues for the purpose of bonding wood grew economically insignificant. Although within the context of ecological aspects, science and research are again taking interest in natural products, there is no general economical trend, with the exception of niche applications such as the restoration of antique objects. The following problems which occur with natural glues have not yet been solved satisfactorily:
• The manufacturing costs of natural binders are clearly higher than those of synthetic adhesives.
• The work-up of animal and plant raw materials gives rise to concern with regards to aspects of hygiene and ecology.
• Natural glues must be improved by the addition of synthetic agents in order to obtain the technical performance required.
• Products originating from different sources may differ considerably in quality.
• Existing facilities for the bonding of wood-based materials must be modified for the application of natural glues.
• As with all other agricultural products, fluctuations in the price and supply of natural adhesives may be relatively important, making planning difficult.
Опубликовано в рубрике 