+ K5 ^1 k7 R6 ^; t. ]4 ~' Z% G生物质塑料可以节约有限的石油能源，但它未必是可降解的；而降解塑料可解决环境有害物排放的问题，但它可能是来源于石油。那么，是否有能够同时满足节能和减排的新材料呢?答案是肯定的，聚乳酸(PLA)就是这样一种鱼与熊掌兼得的新材料。
) c7 b6 z+ \. @7 `7 M1 {8 W/ A4 PBiomass plastics can save limited petroleum resources, but they may not be biodegradable; and degradable plastics can solve the problem of environmentally harmful emissions, but they may be made of petroleum. So, are there new materials that can satisfy both saving energy and reducing emission? The answer is yes, and polylactic acid (PLA) is such a new material.
5 Y, ?6 A+ I7 e6 C6 G聚乳酸是以乳酸为单体经化学合成的新型生物质降解高分子材料——原料乳酸是光学活性物质，有D型和L型两种光学异构体，因此,聚乳酸也有三种异构体:聚D—乳酸(PDLA)、聚L—乳酸(PLLA)和聚D，L—乳酸(PDLLA) 。
& ?- d Y/ z6 s6 s! k& D2 K. rPLA is a new type of biomass degradable polymer material chemically synthesized from lactic acid as monomer—the raw material lactic acid is optically active and has two optical isomers which are D-type and L-type. Therefore, PLA also has three isomers: PDLA, PLLA and PDLLA.
4 k5 i1 n8 O8 {' \% R' J0 F8 {; Q目前常用的聚乳酸产品主要是PLLA和PDLLA两种，前者是结晶性高分子，后者是无定形高分子:在降解方面PLLA慢于PDLLA，在生物相容性方面PDLLA优于PLLA。聚乳酸的玻璃化温度约为55℃,密度约1.25 g/cm3，有良好的抗溶剂性、防潮、耐油脂，不溶于水、乙醇、甲醇等，易水解成乳酸，且无毒、无刺激性，可生物分解吸收、透气性好，还具有一定的抑菌性、阻燃性和易于加工成型。聚乳酸来源于生物质，经过生物降解，最终形成二氧化碳和水，不污染环境，因而被认为是最有发展前途的高分子材料之一，备受国内外关注。9 o- f! V" d( l. `
Currently, the common PLA products are PLLA and PDLLA. The former is a crystalline polymer and the latter is an amorphous polymer. PLLA is slower than PDLLA in terms of degradation and PDLLA is better than PLLA in terms of biocompatibility. PLA’s glass transition temperature is about 55°C and its density is about 1.25 g/cm3. It has the following properties: solvent resistance, moisture resistance, grease resistance, insolubility in water, ethanol and methanol, easy hydrolyzation into lactic acid, innocuity, no stimulation, biodegradable absorption, good permeability, bacteriostasis, inflaming retarding and easy molding. PLA derives from biomass, and it eventually becomes carbon dioxide and water after biodegradation, which does not pollute the environment. Therefore, it is considered as one of the most promising polymer materials and has attracted much attention at home and abroad. |
