H. Ohara et al., Development of industrial production of high molecular weight poly-L-lactate from renewable resources, NIP KAG KAI, (6), 2001, pp. 323-331
This development is related to the method of the industrial production of h
igh molecular weight poly-L-lactate having the applicable properties as com
modity plastics by use of sugars which are derived from renewable resources
. To realize the effect of drawing orientation of films and fibers, high cr
istallinity of the poly-L-lactate is required. In other words, L-lactic aci
d preparation having high optical purity must be used as the raw material t
o produce such high crystal poly-L-lactate. Further, the price of the raw m
aterial should be reasonable one to make the price of such poly-L-lactate r
easonable. For this purpose, we have developed a technology to produce L-la
ctic acid preparation of which optical purity is 99.0 % by a strain of Baci
llus species which has low auxotrophic characteristic. For the industrial p
roduction of poly-L-lactate, LL-dilactide was produced from the pre-polymer
s of low molecular weight poly-L-lactate through the intramolecular transes
terification. In the preparation of the pre-polymers, polycondensation take
s place where the linear mono-, di-, and trimer of lactic acid are totally
refluxed so that the yield of LL-dilactide can be improved, then the temper
ature of the reactor is raised up in three steps, 135, 150, 160 degreesC to
prevent the racemization of L-lactic acid. The high purity of LL-dilactide
is also required to produce high molecular weight poly-L-lactate. The melt
ing crystallization method without a solvent was developed for the purifica
tion of LL-dilactide after consideration of lowering the load on the enviro
nment. Among various intramolecular transesterification catalysts which we
have examined, tin(II) 2-ethylhexanoate showed highest activity and obtaine
d high optical purity LL-dilactide. Ring-opening polymerization of LL-dilac
tide was continuously took place without a solvent resulting in the product
ion of high molecular weight poly-L-lactate of which weight-average molecul
ar weight is 180000 to 200000. In addition, the properties of poly-L-lactat
e and the behavior of its biodegradation in a compost were revealed in this
work.