Recycling and Reusing Waste Polylactic Acid Adds New Ways 　　

On February 28, news from the Qingdao Institute of Bioenergy and Processes of the Chinese Academy of Sciences reported that the research team led by researcher Wang Qinggang of the institute adopted a new strategy for upgrading the chemical cycle of polymer degradation and repolymerization.
The "polymer-to-polymer" approach has successfully realized the recycling of PLA waste to new PLA materials
.

As a typical polymer material derived from renewable raw materials (starch), polylactic acid is gradually developing into a basic bulk material necessary for society, and the problem of post-processing of waste polylactic acid materials has also attracted attention
.

Although polylactic acid can be degraded in nature, this process usually requires a long time and specific degradation conditions, and the degradation products are carbon dioxide and water, which cannot be directly and quickly recycled.
Its degradation is essentially a carbon emission process.

"Most of the previous studies were to convert waste polylactic acid into alkyl lactate, but to obtain high molecular weight polylactic acid materials through this process, it is necessary to hydrolyze alkyl lactate into lactic acid, prepolymerize into oligomers, dimerize Lactide is then polymerized to obtain polylactic acid
.

Although these methods are feasible, they are expensive and inefficient

To this end, the research team prepared a metal zinc catalyst with the best catalytic effect on the basis of previous research
.

The catalyst is bis(hexamethyldisiloxane) zinc, namely Zn(HMDS)₂, which is prepared from zinc and hexamethyldisiloxane as raw materials

Studies have shown that metal zinc catalysts play a decisive role in the degradation and repolymerization process
.

In the process of degradation and repolymerization catalyzed by Zn(HMDS)₂, the polylactic acid polymer chain is controllably degraded into short-chain polymers by alcohol, and the relative molecular weight of the degraded short-chain polymers can be regulated by adjusting the amount of alcohol; alcohol; The introduction of the polymer makes the polymer regain chain-extending activity, and adding different equivalents of lactide during the repolymerization process can precisely control the relative molecular mass of the new polylactic acid obtained

Yang Rulin, a member of the research team, said that the key to this technology is whether polylactic acid can be controllably degraded to a short-chain polymer with a theoretical chain length during the degradation process, and whether the short-chain polymer can be quickly and accurately repolymerized to the target during the repolymerization process.
relative molecular mass to obtain final materials with different properties
.

In addition, the strategy has mild reaction conditions and few side reactions, which reduces the consumption of raw materials for completely reproducing PLA, and maximizes the recycling efficiency of PLA

　　Wang Qinggang said that the degradation and repolymerization strategy not only promotes the development of polymer recycling, but also has broad application prospects in the field of polymer modification and new structural polymer synthesis
.

In the next step, the team will further study to expand the application field of this strategy and develop more efficient polymer recycling strategies