Accelerated late-stage hydrolytic degradation of poly(l-lactide)/poly(d-lactide) stereocomplexes (2023)

Stereocomplex polylactide (SC-PLA), as a popular "green" engineering plastic, has great application potential in various fields due to its excellent physical and chemical properties and durability. However, the application of SC-PLA still faces great challenges, mainly due to its poor melt processability (i.e., weak melt memory effect and extremely low melt viscosity to stimulate exclusive SC crystallization) and lack of necessary functional properties (such as electrical) related conductivity) in some cases. Here we developed a simple and robust strategy by adding carbon black (CB) to an equimolar mixture of poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) to Overcome these obstacles. Interestingly, CB particles can adsorb many PLLA/PDLA segments on their surface, and this strongly adsorbed PLA segments can interact with PLA chains outside the surface to form physical compounds that bind PLLA/PDLA, which can stabilize the PLA chains in the chains. Aligning the melt eventually induces the formation of exclusive SCs during subsequent crystallization. At the same time, CB particles can significantly increase the melt viscosity of the mixture (from 3.9 Pas to 844.1 Pas when measured at 250 °C and 50 Hz). Due to greatly improved melt processability, PLLA/PDLA/CB composites have been successfully injection molded into highly crystalline products with unique SC crystallites and excellent thermomechanical properties. In addition, carbon black particles can also provide excellent electrical conductivity (19.0 S/m) and electromagnetic interference shielding effect (26.6 dB) for composite articles. This work could open a promising avenue for high-performance and multifunctional PLA bioplastics.

In this work, based on poly(LiftDrug model molecules (PLLA) have been studied where the drug model molecule is modified to be more easily dispersed in polymer matrices and possibly directly PLLA degrades. In fact, the above compound consists of a short-chain poly(Man-lactide) (Pyr-D) or PLLA (Pyr-L) were synthesized using the widely used hydrophobic model drug 1-pyremethanol (Pyr-OH) as the initiator for L-ring-opening polymerization (ROP). orMan- lactic acid.¹H-NMR measurements allowed calculation of oligomer molecular masses, which agreed satisfactorily with theoretical values. To examine the effect of synthetic compounds on the final properties of the material, electrospun fibers with different compositions, namely H. Based on pure PLLA, Pyr-OH-containing PLLA, Pyr-L-containing PLLA, Pyr-D-containing PLLA, and Pyr-OH and Pyr-D-containing PLLA fibers by adding specific amounts of various additives to obtain the same pyrene content . Morphological characterization by FE-SEM showed that the addition of the above compounds had no significant effect on the morphology of the fibers. In contrast, fluorescence microscopy measurements revealed different distributions of pyrene-based additives in different samples, namely aggregation of Pyr-OH and uniform distribution of Pyr-L and Pyr-D. Check the thermal properties of the fibers by DSC measurements. In general, annealing at 80 °C for 4 hours was found to increase the crystallinity of the system. Furthermore, fibers containing Pyr-D additives were found to be characterized by partial stereocomplexation of the PDLA chains of Pyr-D bound to the PLLA matrix, which was also confirmed by X-ray diffraction analysis. Enzymatic degradation tests performed on annealed and non-annealed samples showed that heat treatment as well as addition of Pyr-D significantly reduced the fiber degradation rate. Thus, over time, pyrene release monitored by UV measurements was associated with systemic degradation and stereocomplexation as it was much slower in Pyr-D-containing fibers.

The effect of UV light on polylactide/poly(methyl methacrylate) (PLA/PMMA) blends produced by melt extrusion, with particular focus on the specific effect of the PLA stereocomplex on the photochemical behavior of the blends, is focus of this work. Preparation of stereocomplexable polylactic acid by melt blending high molecular weight poly( ) .Lift-Lactid) (PLLA), Poly (Man-lactide) (PDLA) and PMMA. The photochemical behavior of the resulting PLA/PMMA mixture was studied by irradiation under photooxidative conditions (λ>300 nm, temperature 70 °C and presence of oxygen). Chemical changes induced by UV exposure were analyzed using infrared spectroscopy (IR) and size exclusion chromatography (SEC). Check for morphological changes using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The results showed that PDLA and PMMA had no effect on the photooxidation rate of PLLA. However, PLA stereocomplexes have a strong influence on the morphology of the mixture during photochemical aging.

The hydrolysis behavior of polylactic acid (PLA) films with different degrees of crystallinity (~0, 30 and 40%) containing hydrophobic fluoropolymers was investigated by contact angle measurements and FTIR evaluation of hydrophobicity and water absorption and the development of the mean Molecular weight, morphology and thermal properties were examined. The results showed that the hydrophobic fluoropolymers enhanced the hydrophobicity of the PLA surface and increased the water contact angle by about 20°, but they did not reduce the water absorption of the PLA host. The hydrolysis rate of the samples was affected by the crystallinity of the PLA component and the dispersibility of the hydrophobic fluoropolymer. For amorphous samples, fluoropolymers can disperse well in PLA matrix and accelerate the hydrolysis of PLA components. Amorphous PLA has a hydrolysis rate of 0.0335 weeks⁻¹, while the rate increases to 0.0458 for the amorphous sample with hydrophobic fluoropolymer⁻¹. For crystalline samples, pure PLA hydrolyzes faster than the mixture. For example, the crystallization rate of PLA at 90°C is 0.0423 weeks⁻¹while the value of the mixture with PLASecond-PFMA₁₀and PLASecond-PFMA₂₀0.0325 and 0.0260 weeks, respectively⁻¹The difference between and blends is related to the dispersibility of the fluoropolymers, since poorly dispersible fluoropolymers have better hydrolytic stability than better dispersible fluoropolymers.

The biodegradation behavior of polylactic acid (PLA) mixed with starch and wood flour in outdoor soil has been extensively studied. As a result, starch provided biofuel for the growth of microorganisms in the soil and accelerated the degradation rate of PLA more than wood flour. As the starch content increased, the weight loss increased and more ridges and cavities appeared in the morphology. X-ray photoelectron spectroscopy (XPS) analysis revealed that the change in O/C ratio was controlled by starch biodegradation and PLA hydrolysis, and was a concomitant process. The mechanical strength of all mixtures showed a similar trend, fitting a first-order exponential decay model. The model has been shown to be in good agreement with the experimental results, as the correlation coefficient is above 0.99, and the model can support an efficient method for estimating the shelf life of starch/wood flour/PLA mixtures.

A simple and clean polylactide (PLA) stereocomplexation technique can be easily integrated into continuous industrial processes used to make films, fibers, and other plastic products. With this approach, complete stereocomplexation of high-molecular-weight PLA can be achieved by a simple heat treatment, enabling cost-effective and industrially scalable production of durable PLA products. Currently, PLA products have limited industrial use due to their high sensitivity to water and heat, and cannot compete with petroleum-derived products. Poly (Lift-lactic acid) (PLLA) and poly(Man- Lactic acid (PDLA) can effectively reduce the water sensitivity and heat sensitivity of common PLLA products. However, many stereocomplexation processes require hazardous solvents or nucleating agents, and thus are costly, complex, and have little potential for industrialization in the short term. In addition, for PLA with a weight average molecular weight less than 1 × 10, most achieved complete stereocomplexation⁵.In this study, the viscosity-average molecular weight of PLLA and PDLA is 3×10⁵Complete stereocomplexation (sc) by simple heat treatment. Compared with PLLA fibers, sc-PLA fibers had a 60 °C higher softening point and significantly improved thermal and hydrolytic stability. Correlations were also found between heat treatment temperature, degree of stereocomplexity, and properties of sc-PLA fibers. This clean technology enables the production of commercially viable bio-based plastics on an industrial scale.

Polymers, Band 56, 2015, S. 245-251

The α″ phase of syndiotactic polystyrene (α″sPS) is a frustrated “superstructure” that accommodates three triplets (three clusters of three chains, or nine chains) in a triangular unit cell. thisHongkongIn addition to the sharp points, there are a series of diffuse points in the 1/3 and 2/3 places between the sharp points in the zero electron diffraction pattern of α″sPS single crystal. The diffuse points correspond to the intersection points of the fringes. They are due to the Structural perturbations associated with the "frustrated" triplet state in cells with triplet symmetry but in a hexagonal symmetric environment. Thus, two equivalent crystal positions for this triplet state are possible, corresponding to 0° and 180° (or 60°) azimuth setting. Modeling of the diffraction features associated with this perturbation reproduces the experimentally observed patterns in minute detail. Thus, the frustrated features of the sPS-α'' phase structure explain the very detailed sharp reflection and diffraction patterns of Diffuse component.

Polymers, Volume 55, Issue 20, 2014, Pages 5111-5124

P(TMC-cooperative-CL) was studied using subcutaneous implantation in various compositionsI live in. To elucidate the role of enzymes in the degradation behavior of copolymers, hydrolysis and enzymatic degradation processes were also carried out. Monitor mass loss, changes in molecular weight and polydispersity, and compositional changes upon degradation. Changes in thermal and mechanical properties of the samples were also examined. The results showed that preferential cleavage of ester bonds resulted in faster degradation under hydrolytic and enzymatic conditions. In addition, P(TMC-cooperative-CL) has a higher degradation rate in the presence of lipase because it cleaves the ester bond and acts as a surfactant in the diffusion of degradation products in water.I live in，P（TMC-cooperative-CL) depending on their composition - copolymers with higher TMC content degrade mainly by surface erosion. Mass depletion was observed in people with higher CL levels. After degradation, the mechanical properties and thermal stability of the copolymer decreased, but the Tm and crystallinity increased due to the preferential degradation of the amorphous region. P(TMC-cooperate-CL) have tunable degradation rates and remain promising candidates for clinical subcutaneous implants, especially through shape stabilization work.

Polymer Degradation and Stability, Volume 177, 2020, Item 109186

European Polymer Journal, Band 89, 2017, S. 381-398

This article summarizes extensive research on the hierarchical structures formed in polylactic acid (PLA)/polyethylene glycol (PEG) mixtures. This system is of interest not only for improving its properties but also for its use as a biodegradable material. In general, crystalline polymers often form different types of structures at different size scales. On the nanometer scale of 0.1 to 10 nm, crystalline polymers form layered crystals. The most appropriate technique to study these structures is X-ray scattering, including wide-angle and small-angle X-ray scattering. On the scale of microns and even larger, the flakes stack and coalesce into spherulite structures. In such cases, atomic force microscopy and X-ray computed tomography are powerful detection methods. Details of the higher-order crystal structures of PEG crystallites in 100% PEG and PLA/PEG blends are reported. Then the structural changes during heating and cooling under normal and high pressure are discussed. An advantage of using SAXS is that meaningful structural analysis can be performed, thus the discrete distribution of lamellar thickness as a function of temperature was evaluated for 100% PEG samples and PLA/PEG blends of different compositions.

Journal of Mechanical Behavior of Biomedical Materials, Paragraph 37, 2014, S. 219–225

Using a solution casting process followed by thermal homogenization to produce 1:1 Poly() blend and unblend films.Man-Lactid) (PDLA) 和 Poly(Lift-lactide) (PLLA) with three different molecular weights, and its thermal and mechanical properties were determined by differential scanning calorimetry (DSC) and tensile tests. According to literature records whenrice_wBelow 1.0×10⁵At g/mol, only stereocomplex crystallization occurs, and at higher levels, isomorphs and stereocomplex crystallites coexist. To promote crystallization as isomorphs in pure polylactide and stereoselective crystallization as stereocomplexes in the case of non-hybrid films to achieve varying degrees of crystallinity, several annealing heat treatments were performed in this work . Highly stereocomplexed mixtures were discovered by stereospecific heat treatment. It was found that regardless of the molecular weight, the toughness of the 1:1 blend was significantly higher than that of the unblended film. For example, in the stereocomplex mixture B2-5050, poly(Lift-Lactid) 和 Poly(Man- lactide) ofrice_w=1,2×10⁵g/mol, relative to its non-mixed poly(Lift-lactide) counterpart crystallizes as homocrystalline. This improvement in mechanical properties in stereocomplex mixtures is not due to an intrinsic property of the crystalline polymorph type, but to the presence of a higher density of intergranular compounds through the flowing amorphous phase, d stereocomplexed samples At the same time, the strength and elongation at break are improved.

Polymers, Band 60, 2015, S. 221-227

Poly (Lift-lactic acid)/poly(Man-lactide) = 5/5 mixture results in abundant stereocomplex crystals with a small trace of isomorphism. In contrast, isomorphs with the same composition dominate during cold crystallization in solution-cast and melt-quenched films. Using FTIR technique, it was confirmed that poly(Lift-Lactid) 和 Poly (Man- Induction of lactide chains in electrospun composite fibers due to the interaction of methyl and carbonyl groups. The intermolecular order acts as a precursor to initiate strong stereocomplex formation in electrospun hybrid fibers above the glass transition temperature. In addition, the formation of stereocomplexes in electrospun hybrid fibers follows one-dimensional growth due to the confinement effect in individual fibers.