Vocabulary:

(1)– технологія гнуття

(2) – пропарювання

(3) – розпрямлятись

(4) –слід дотримуватись

(5) – поручні

Read and translate the text.

Adhesives

In the technical sense “glue” and “adhesive” are now used as synonyms to describe many different substances which are used for holding parts together such as in the manufacture of furniture.

Organic polymers of either natural or synthetic origin are the main chemical ingredients of wood adhesives.

Glues of natural origin. Animal glues are made from hide(1) and skin(1) fleshings, bones(2) and horns(3). The glue is available in solid, jelly, or liquid forms. The solid form is prepared for use by mixing with water and are simply melted at the proper temperature. Liquid glues are ready for use as cold adhesives. Animal glues can give strong joints in the dry state, but they have little or no moisture resistance. Blood albumin glue(4) is a hot-press plywood adhesive(5) and until the introduction of synthetic resins, it was the most water-resistant glue. Casein glues are of great importance, they rank second only to the synthetic resins. Casein is still widely used in plywood manufacture in the Americas, Australia, India. Casein is a protein derived from soured milk.

The glues of natural origin have been used as adhesives for centuries and are still in use today, although they have been replaced mostly by adhesives made with synthetic polymers. The first wood adhesives based on synthetic polymers were produced commercially during the 1930s. These adhesives are stronger and more durable, have much greater resistance to water than adhesives from natural polymers.

According to the mechanism of glueing, synthetic polymers (resins) are sub-divided into thermoplastic and thermosetting(6) types. Whether the base polymer thermoplastic or thermosetting, has a great influence on how an adhesive will perform in service. Thermoplastics are polymers that soften and flow when heated, then harden again by cooling. They generally have less resistance to heat, moisture and long-term static loading as compared to thermosetting polymers. Thermosetting polymers make very good structural adhesives because they undergo irreversible chemical changes and on reheating, they do not soften and flow again. They have resistance to moisture, chemicals and high strength. They are rigid enough to support long-term static loading without deforming.

According to the base material used, synthetic resins are classed into: urea-formaldehyde (UF)(7), melamine- formaldehyde (MF), phenol- formaldehyde (PF), epoxy, hot-melt(8) and others. According to their physical state, they are divided into liquid, powder, paste-like and film. According to the degree of solubility: water-soluble, alcohol-soluble and non-soluble. According to the character of setting: cold-setting (9)(that sets at temperatures below 20 degrees), hot-setting(10) (that requires a temperature above 100 degrees to set in).

Applications. PF-resin requires longer press time and higher press temperature. Products with PF may have lower dimensional stability. The dark colour of PF-resins may make them unsuitable for decorative product application such as panelling and

furniture. UF-resins are the most widely used adhesives for composite wood products.

The light colour of UF-resins makes them quite suitable for the manufacture of decorative products.