Effects of heating rate and temperature on product distribution of poly-lactic acid and poly-3-hydroxybutyrate-co-3-hydroxyhexanoate

Abstract

In this study, poly-lactic acid (PLA) and poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBH) were pyrolyzed at various temperatures (300, 350, 400, 500, 600, and 700 °C) and heating rates (5, 10, 20, 30, and 40 °C min−1) using a pyrolysis–gas chromatograph/mass spectrometer (Py–GC/MS). The results revealed that the main pyrolysis products of PLA were acetaldehyde, lactide (including meso-lactide and d-, l-lactide), and oligomers. Crotonic acid and its oligomers accounted for most of the PHBH pyrolyzates. The pyrolysis temperature significantly correlated with the product distribution, but the heating rate had a small effect on the product distribution. Lactide and crotonic acid were two kinds of high-value chemicals, and their highest yields were obtained at 400 and 600 °C with 29.7 and 72.6 area %, respectively. Secondary reactions could not be neglected at 700 °C, and acetaldehyde and crotonic acid decreased to 65.0 and 69.6 area %, respectively. These results imply that pyrolyzate selectivity can be controlled by temperature management during pyrolysis.

Selective recovery of pyrolyzates of biodegradable (PLA, PHBH) and common plastics (HDPE, PP, PS) during co-pyrolysis under slow heating

“…Meso -lactide is typically produced through a free radical reaction, and D- and L- lactides are produced by transesterification reactions 24 , 39 . The produced oligomers were considered cyclic lactide, with reference to the works of Shao et al 26 and Arrieta et al 40 . The main pyrolyzates of PHBH were propylene, isocrotonic acid, crotonic acid, 2-hexenoic acid, and their dimers (Fig.…”

“…For poly( β -hydroxybutyric acid) (PHB) pyrolysis, the dominant reaction pathway is stereoselective cis -elimination, yielding crotonic acid and its oligomers 25 . Shao et al 26 examined the pyrolysis behavior of PLA and poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBH) with various temperatures and heating rates and demonstrated that the highest yields of lactide and crotonic acid, high-value chemicals from PLA and PHBH, are obtained at 400 and 600 °C, respectively. Saeaung et al 27 investigated the catalytic and non-catalytic pyrolysis of PLA and reported that 79% lactide can be extracted from PLA through catalytic pyrolysis with zeolite at 400 °C.…”

Evaluation of Thermal Decomposition Kinetics of Poly (Lactic Acid)/Ethylene Elastomer (EE) Blends

“…Considering that D1 and D4 are diffusional processes, it could be assumed that the reaction rate is higher than the reaction front propagation [64,65]. This result diverged from Alhulaybi et al [31], Shao et al [66], and Gharshallah et al's [67] findings, which suggested that PLA thermal degradation is more likely to happen as R2, R3, and F2 mechanisms, respectively. The divergence could be due to the scission of some PLA chains during processing by shear forces, reducing the average molecular weight, which would explain the lower degradation activation energy (E a ) value found for PLA in this work (Table 7).…”

Characteristics of the steam degradation of poly(lactic acid) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

“…Pyrolysis is a unique technology for recovering lactides from PLA waste through thermal depolymerization [21,22]. However, the low recovery rates of pyrolysis methods have limited their practical application [23,24]. To increase the recovery efficiency, catalytic pyrolysis and co-pyrolysis have been proposed for recycling PLA.…”

“…Poly(3-hydroxybutyrateco-3-hydroxyhexanoate) (PHBH) is a member of the PHA family with a broader processing window and good thermal stability [28]. Previous studies have revealed high production of crotonic acid, a monomer of PHBH and poly(3hydroxybutyrate) (PHB), at temperatures exceeding 600 °C [24,29]. Therefore, lowering the production temperature of crotonic acid and increasing its yield are highly desirable.…”