CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND

WITH COMMERCIAL EXAMPLES

Blending procedures had been employed since time immemorial. The principle of blending is geared towards achieving property averaging. A blend is therefore the physical mixture of two or more substances, without a chemical bond. Linseed oil, a triglyceride of unsaturated fatty acids, is heated with a brittle resin, usually an unsaturated C20 mono carboxylic acid (Mantell, Kopf, Curtis and Rogers, 1942). The resin itself could be used as a coating, but the linseed oil is incorporated to reduce the brittleness of the product. On the other hand, the linseed oil by itself forms an oily, slow-to-harden coating. Thus, the principle of property averaging (blending) was recognized a long time ago. The resin contains unsaturation and, presumably during the heating with the oil and the subsequent oxidative cross-linking, is incorporated covalently. Nevertheless, no segregation occurs and clear, tough, films of high molecular weight result. Many modern vanishes use phenol-formaldehyde resins rather than natural resins. Modification of the basic phenol structure is required in order to obtain solubility of the resin in the linseed oil. parasubstitution with tert-butyl, phenyl, and other hydrocarbon groups increases the aliphatic character (reduces solubility parameter) enough to achieve solubility.

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