Selective Depolymerization and Effects of Homolysis of Poly(L-lactic acid) in a Blend with Polypropylene

Blends of poly(L-lactic acid) (PLLA) and polypropylene (PP), which are candidates for the practical use of PLLA, were investigated for selective degradation of PLLA, resulting in quantitative conversion of PLLA components into cyclic monomers, lactides, using magnesium oxide (MgO) as a depolymerization catalyst. Obviously, the catalyst MgO selectively accelerated only the PLLA depolymerization in the blends, dominantly generating L,L-lactide as a volatile product and separating the PP component. Expected effects of homolysis in the blend system were also determined as slight changes in activation energy of degradation for both the components and through the suppression of degradation by an antioxidant

Thermal Degradation Behavior of Poly(Lactic Acid) in a Blend with Polyethylene

Poly(L-lactic acid) (PLLA) is a candidate for feedstock recycling materials, because it easily depolymerizes back into the cyclic monomer, L,L-lactide. To examine the recycling of PLLA from blends with other kinds of polymers, a polymer blend of PLLA and linear low-density polyethylene (LLDPE) was prepared and thermally degraded with a degradation catalyst: magnesium oxide (MgO) in a thermogravimeter/differential thermal analyzer (TG/DTA) and pyrolysis-gas chromatograph/mass spectrometer (Py-GC/MS). To clarify the influence of the LLDPE ingredient in the blend, the thermal degradation data were analyzed kinetically using two simulation methods: integration and random degradation analytical methods. From the results, it was found that PLLA was effectively depolymerized in the presence of MgO into L,L-lactide with a low racemization ratio and that LLDPE had no effect on the feedstock recycling of PLLA

Characteristic Chain-End Racemization Behavior during Photolysis of Poly(L-lactic acid)

Photolysis of poly(L-lactic acid) (PLLA) has many unclear points, such as the degradation mechanism, kinetics, products, and racemization mechanism. To clarify these features of PLLA photolysis, we examined the relationship between photolysis and racemization. The hexad stereosequential analysis of photodegraded PLLA was investigated to specify the racemized positions within a chain in comparison with hydrolysis and thermal degradation. Results from 13C NMR spectra of UV-irradiated PLLA samples indicated that the samples have racemized D-lactate units at chain ends. From the comparison of racemization behavior among photolysis, hydrolysis, and thermal degradation, it was confirmed that the preferential racemization behavior of each of these three degradation processes is characteristic and distinct, being identified as chain-end racemization, poor racemization, or internal-unit racemization, respectively. The characteristic chain-end racemization behavior of photolysis was first confirmed in this study

Effects of MgO Catalyst on Depolymerization of Poly-L-lactic Acid to L,L-Lactide

To control the depolymerization of poly-L-lactic acid (PLLA) into L,L-lactide, effects of altering the physical and chemical properties of magnesium oxide (MgO) on its ability as a catalyst were investigated. Four kinds of MgO particles: MgO-heavy, 0.2, 0.05, and 0.01μm, were used having primary particles of different dimensions, surface areas, and chemical structures/species. Thermo-gravimetric profiles of PLLA/MgO composites shifted into a lower temperature range due to an increase in the catalytic surface area resulting from a decrease in the dimensions of the MgO particles. However, decreasing the dimensions caused frequent side reactions with unfavorable products: cyclic oligomers and meso-lactide, due to the presence of different chemical structures/species. Heat treatment of the MgO particles effectively suppressed the oligomer production and enhanced the L,L-lactide production, but also accelerated the meso-lactide production at lower temperatures. These results indicate that the surface properties of MgO considerably influence the depolymerization of PLLA, with the catalytic behavior of MgO controllable by heat treatment and selection of the depolymerization conditions

Oligomerization of Poly(L-lactic acid) by High-Pressure Steam Treatment for Feedstock Recycling

High-pressure steam hydrolysis of a poly(L-lactic acid) (PLLA) / poly(bisphenol A carbonate) (PC) (50:50 wt/wt) immiscible blend was investigated as a pre-treatment process before feedstock recycling of the PLLA component, resulting in the selective oligomerization of the PLLA component. After the pre-treatment by steam, the PLLA component was preferentially hydrolyzed in a manner of autocatalytic random degradation, whereas the PC component showed no change in molecular weight. This characteristic hydrolysis behavior of the blend will facilitate the crushing of moldings and subsequent feedstock recycling of PLLA.The 5th International Symposium on Feedstock Recycling of Plastics & Other Polymeric materials(ISFR2009), 11th–14th October, 2009, Chengdu, Chin

Effects of poly(L-lactic acid) hydrolysis on attachment of barnacle cypris larvae

Poly(L-lactic acid) (PLLA) applied to immersed solid surfaces in seawater inhibited colonization by barnacles due to the slow-release property of lactic acid. The effect of molecular weight of PLLA on antimacrofouling activity was confirmed for the first time, with the lowest molecular weight PLLA producing the lowest attaching ratio of cypris larvae of Balanus amphitrite. From the direct addition of lactic acid into a culture of cypris larvae, it was found that the anti-barnacle settlement effect was due to the action of slow-released lactic acid to cypris larvae. The anti-macrofouling function of low molecular weight PLLA was also confirmed in a natural sea environment

Quantitative Evaluation of Photodegradation and Racemization of Poly(L-lactic acid) under UV-C Irradiation

To obtain details of poly(L-lactic acid) (PLLA) photodegradation behavior, PLLA films were irradiated by UV-C light (λ = 253.7 nm) to directly excite carbonyl groups, resulting in a rapid decrease in the molecular weight accompanying a gradual decrease in the optical purity of monomeric units in the chains. The racemization during the photodegradation was first detected as a result of the chain scission by irradiation. From quantitative analyses of the molecular weight and the monomeric unit composition, it was found that the chain scission ratio and the D-lactate unit ratio increased in parallel during the irradiation, suggesting that approximately one D-lactate unit formed for every chain scission. From a mechanistic consideration, the racemization equilibrium was proposed to occur at both carboxyl and hydroxyl chain ends

Racemization Behavior of L,L-Lactide during Heating

To control the depolymerization process of poly (L-lactic acid) into L,L-lactide for feedstock recycling, the racemization of L,L-lactide as a post-depolymerization reaction was investigated. In the absence of a catalyst, the conversion to meso-lactide increased with increase in the heating temperature and time at a higher rate than the conversion into oligomers. The resulting high composition of meso-lactide suggests that the direct racemization of L,L-lactide had occurred in addition to the known racemization mechanism that occurs on the oligomer chains. In the presence of MgO, the oligomerization rapidly proceeded to reach an equilibrium state between monomers and oligomers. The equilibrium among L,L-, meso-, and D,D-lactides was found to be a convergent composition ratio: L,L-:meso-:D,D-lactides = 1:1.22:0.99 (wt/wt/wt) after 120 min at 300 °C. This composition ratio also indicates that, in addition to the known racemization reaction on the oligomer chains, direct racemization among the lactides is also a frequent occurrence

Butylated lignin as a compatibilizing agent for polypropylene–based carbon fiber-reinforced plastics

金沢大学理工研究域生命理工学系Lignin is a renewable resource, but it is also considered a waste or a very-low-value material. Herein, we propose a lignin-derived compatibilizing agent as an alternative to the current compatibilizing agents. We prepared a polypropylene-based carbon fiber-reinforced plastic (CFRP) with butylated lignin (C4 lignin). Upon the addition of C4 lignin, the dispersion of carbon fiber into the matrix, and the adhesion between the carbon fiber and the matrix were greatly improved. As a result, the tensile strength of the CFRP prepared with C4 lignin was greater than that of the CFRP without lignan lignin (37.1 compared to 40.2 MPa). This value is close to that of CFRPs prepared with maleic anhydride-modified polypropylene (40.9 MPa), an existing compatibilizing agent. C4 lignin is a promising candidate for biomass-derived compatibilizing agents for polypropylene-based CFRPs.Embargo Period 6 monthsThis paper has supplementary information