树脂
维基百科，自由的百科全书
樹脂是一種來自多種植物，特別是松柏類植物的烴(碳氫化合物)類的分泌物。因為它特殊的化學結構和可以作為乳膠漆和膠合劑使用而被重視。它是多種高分子化合物的混合物，所以有不同的熔點。樹脂可分為天然樹脂和合成樹脂兩種。本身只有天然樹脂這一種，但隨著化工的發展，有很多由人工合成的聚合物產生，當中有些聚合物的化學性質及物理性質會和天然樹脂很相似，因此，聚合物會被稱為合成樹脂。
目录 |
[编辑] 產生
樹木生產樹脂有不同的理由，因此科學家為此作出不同的觀點。較多科學家認同的是，植物以樹脂密封傷口，以殺死昆蟲及防止真菌入侵，以及消除生產過多的代謝物，但到目前為止，還沒有一個肯定的答案。
為了提取樹脂，一般也要在樹皮切一刀，並要淺淺的割出一條旋轉向下的管道（稱為樹脂道），令樹脂流出後，沿樹脂道流動，直至滴到收集處。假如樹皮太硬的話，可能要使用酒精（如：甲醇和乙醇等）把樹皮的纖維組織軟化或溶解，才能收集樹脂。
樹脂滴下後，會和空氣產生化學反應，會續漸硬化，形成固體。
而樹脂容易硬化的特性，使它一直應用在乳膠漆及膠合劑之中
[编辑] 化學性質
樹脂是一種黏性的液體, 其主要组分为較容易揮發的萜烯类物质,使得树脂具有特殊的味道。还含有溶解在萜烯中的不揮發的黏性固體，所以当树脂暴露在空气中，萜烯类物质挥发掉，使得树脂黏度增大，形成固体。當中，它組成的烯中，以雙環狀的烯化合物為主。如：alpha-Pinene, pinene(beta-pinene), carene(delta-3 carene)及sabinene； 單環狀的烯化合物為其次，如：檸檬油精及香油腦；及更少的產物，如：tricyclic sesquiterpene longifolene, caryophyllene 和 cadinene(delta-cadinene)。使用分餾法可以分開分子量不同的餾份，以作不同的用途。如一些餾份的樹枝酸含量較高，可作其他用途，便以分餾法分餾出來。
A few plants produce resins with different compositions, most notably Jeffrey Pine and Gray Pine, the volatile components of which are largely pure n-heptane with little or no terpenes. The exceptional purity of the n-heptane distilled from Jeffrey Pine resin, unmixed with other isomers of heptane, led to its being used as the defining zero point on the octane rating scale of petrol quality. As heptane is explosively flammable, distillation of resins containing it is very dangerous. Some resin distilleries in California exploded because they mistook Jeffrey Pine for the similar but terpene-producing Ponderosa Pine. At the time the two pines were considered to be the same species of pine; they were later classified as separate species in the mid to late 19th century.
Some resins when soft are known as oleo-resins, and when containing benzoic acid or cinnamic acid they are called balsams. Other resinous products are in their natural condition mixed with gum or mucilaginous substances and known as gum resins. Many compound resins have distinct and characteristic odours, from their admixture with essential oils.
The hard transparent resins, such as the copals, dammars, mastic and sandarac, are principally used for varnishes and cement, while the softer odoriferous oleo-resins (frankincense, elemi, turpentine, copaiba) and gum resins containing essential oils (ammoniacum, asafoetida, gamboge, myrrh, and scammony) are more largely used for therapeutic purposes and incense.
Certain resins are obtained in a fossilized condition, amber being the most notable instance of this class; African copal and the kauri gum of New Zealand are also procured in a semi-fossil condition.
[编辑] 衍生性的商業產品
Solidified resin from which the volatile terpene components have been removed by distillation is known as rosin. Typical rosin is a transparent or translucent mass, with a vitreous fracture and a faintly yellow or brown colour, non-odorous or having only a slight turpentine odour and taste. It is insoluble in water, mostly soluble in alcohol, essential oils, ether and hot fatty oils, softens and melts under the influence of heat, is not capable of sublimation, and burns with a bright but smoky flame. This comprises a complex mixture of different substances including organic acids named the resin acids. These are closely related to the terpenes, and derive from them through partial oxidation. Resin acids can be dissolved in alkalis to form resin soaps, from which the purified resin acids are regenerated by treatment with acids. Examples of resin acids are abietic acid (sylvic acid), C20H30O2, plicatic acid contained in cedar, and pimaric acid, C20H35O2, a constituent of gallipot resin. Abietic acid can also be extracted from rosin by means of hot alcohol; it crystallizes in leaflets, and on oxidation yields trimellitic acid, isophthalic acid and terebic acid. Pimaric acid closely resembles abietic acid into which it passes when distilled in a vacuum; it has been supposed to consist of three isomers.
[编辑] 人造的樹脂
合成樹脂是一種與天然樹脂十分相似的材料——也是能硬化的黏性液體。以酯化作用或含脂肪酸的鹼金屬鹽的皂，再用一些有機化合物，能量產人造的樹脂。
最優秀種類是環氧樹脂，透過聚合物重合反應或者聚合作用，作為膠合劑和混合物的一個熱固性聚合物使用。
One more category, which constitutes the 75 % of resins used, is Unsaturated Polyester Resin. Ion exchange resin is another important class with application in water purification and catalysis of organic reactions.
