A comparison is made between available literature and present results of the three major types of
polylactide (PLA) degradation giving a compiled view on the details of degradation mechanisms with
relation to explicit factors affecting degradation. The temporal decrease of molar mass has been analyzed
under isothermal conditions at 220 C, biological and photodegradation conditions using a polylactide
(PLA) with w4 mol% D units. The decrease of molar mass with time during biodegradation follows a first
order process (M ¼ Moekt) while the molar mass of specimens tested during thermal and photodegradation
follows a second order law (1/M ¼ (1/Mo) þ kt) Literature data obtained in similar degradation
conditions were also adequately fitted with these equations. This allows us to conclude that the
main step in the three types of degradation is a random chain excision, with some differences in the
algebraic functionality. Under the degradation conditions tested, the degradation rate follows the
progression thermal > photo > biological. For equivalent molar mass, the effect of degradation type on
cold crystallization and melting is significant indicating that degradation cannot be explained by a solely
outcome of chains breakage and molar mass reduction. This feature is especially prominent when the
linear growth rates of specimens subjected to bio or photo degradation are compared. Anhydride groups
that are formed during photodegradation decrease the crystallization rate compared to biodegraded
specimens of equivalent molar mass. The molar mass dependence of the maximum growth rate follows
a power law with exponents 1.3 for bio and 1.0 for photodegraded specimens, representative of semientangled
systems. The temperature coefficient of the growth rate, analyzed according to secondary
nucleation leads to a linear dependence for bio and photodegraded specimens, and to values of the
surface free energy of crystallites that decrease from w85 to 55 erg/cm2 with decreasing molar mass.
Combinations of molar mass characterization, FTIR, and thermal and crystallization rate analysis are
proven useful strategies to assess and discriminate macroscopic changes of PLA structure induced by
different types of degradation. This work also underlines the importance of analyzing the linear growth
rates as a parameter that uncovers specific structural changes during degradation.