Resin << REHZ uhn >> is a useful substance that is typically gummy, oily, sticky, or waxy. Resins are used in varnishes, medicines, soaps, paints, and many other products. There are two kinds of resins, natural resins and synthetic (artificial) resins.
Natural resins
are mostly viscous (slow-flowing) liquids. They may be divided into three main groups: (1) resins that flow from plants as the result of wounds; (2) resins extracted from wood by solvents; and (3) fossil resins found with the preserved remains of animals and plants. A scale insect of the acacia tree also produces a resin, called lac.
Gum resins often have been used in medicines. Such resins include asafetida, aloe, and the gum of the balsam tree. However, a person should consult a doctor or pharmacist before using such medicines.
Rosin is a solid resin processed from several varieties of pine trees. It is used in paints, varnishes, and printing inks. It is also applied to the bows of stringed instruments to keep the bow from slipping across the strings.
Oleoresins are resins combined with fragrant oils from plants. They are used in turpentine and tar.
Synthetic resins
have largely replaced natural resins. They are a large group of chemical compounds that includes most of our common plastics. These resins may be made as fibers or films. They can also be molded into a great variety of shapes, ranging from pocket combs to automobile bodies. Manufacturers use these compounds in paints and adhesives and as coatings for cloth, paper, metal, and flooring.
Synthetic resins consist of many simple molecules linked together to form large, complex ones. Scientists call such molecules polymers. The term comes from the Greek words poly, meaning many, and meros, meaning part. A polymer’s nature is determined by the type of molecules it contains and by the order in which they are connected. If a substance consists of long, fibrous molecules, the substance is tough but softens when heated. If the molecules form long chains with many cross-links (connections between the chains), the resin is hard and brittle, and it sets when heated. If few cross-links form, the resin usually is elastic. Resins with short, chainlike molecules are gummy or waxlike.
Manufacturers make synthetic resins using coal, natural gas, petroleum, wood, salt, air, and water. Complicated processes change these common materials into a variety of chemicals. The chemicals are then combined to form the complex molecules of a resin. Manufacturers often alter a synthetic resin’s original properties before making it into marketable items. They do so by combining the resin with fillers, colors, lubricants, and other materials and by treating it with heat.
