Depolymerization of lactic acid oligomers into lactide: Epimerization, stereocomplex formation, and nature of interactions of oligomers

Nitrogen Plasma Treatment of Composite Materials Based on Polylactic Acid and Hydroxyapatite

The effect of surface modification by an arc discharge plasma in a nitrogen flow with treatment durations of 5 and 10 min on the physicochemical properties and biocompatibility of the surface of composites based on polylactic acid and hydroxyapatite (PLA/HA) with different mass ratios (80/20, 70/30, 60/40) has been investigated. The aim of this work was to show the correlation between the changes of the physicochemical characteristics (chemical compound, morphology, wettability) of the surface layer of the PLA/HA composites and the cell viability (macrophages) in the presence of the plasma-modified materials. The dependence of alterations of the functional properties (wettability, biocompatibility) on the change in the chemical composition under the plasma exposure has been established. The chemical composition was studied using X-ray photoelectron spectroscopy (XPS), the surface morphology was researched with scanning electron microscopy (SEM), and the wettability of the composite's surface was analyzed by measuring the contact angle and surface energy calculation. In addition, the viability of macrophages was investigated when the macrophages from three donors interacted with a modified PLA/HA surface. It was found that the formation of the new functional groups, -C-N and N-C=O/C=O, improves the wettability of the surface of the composites and promotes the viability of macrophages in the presence of the composite materials. The fundamental principles for obtaining promising materials with the required properties for eliminating bone defects have been created.

Synthesis and characterization of lactide from Bacillus amyloliquefaciens brewed lactic acid utilizing cheap agricultural sources

Lactic acid (LA) is a nifty molecule with an eclectic range of applications in innumerable industries and is produced through biological and chemical processes. Factually, LA is converted into lactide (LAC), which is the precursor for polylactic acid (PLA). PLA is considered one of the first-rate replacements for petroleum-based products and is believed to be environmentally sustainable. Nevertheless, it has always been challenging due to increased PLA productivity costs. Reduction in the LA and LAC production price directly echoes the production price of PLA. Therefore, low-cost LA and LAC production methods have to be found to produce PLA effectively. Hence, this study uses cheap agricultural sources derived microbial LA to make LAC through dimerization. Produced LAC was analyzed through FT-IR, NMR, TGA and XRD. FT-IR results revealed that the successful dimerization of LA to LAC, NMR analysis revealed that the aligning of methine and methyl groups in produced LAC, TGA analysis exposed that the microbial LAC has more thermal stability than the commercial LAC, XRD results showed that the produced LACs are crystalline with 32% and 42% crystallinity. To the best of our acquaintance, this manuscript is pioneering one to describe LA production through microbial fermentation and uses this monomer to produce LAC through dimerization.

Nondestructive Sequencing of Enantiopure Oligoesters by Nuclear Magnetic Resonance Spectroscopy

Sequence-defined synthetic oligomers and polymers are promising molecular media for permanently storing digital information. However, the information decoding process relies on degradative sequencing methods such as mass spectrometry, which consumes the information-storing polymers upon decoding. Here, we demonstrate the nondestructive decoding of sequence-defined oligomers of enantiopure α-hydroxy acids, oligo(l-mandelic-co-d-phenyl lactic acid)s (oMPs), and oligo(l-lactic-co-glycolic acid)s (oLGs) by ¹³C nuclear magnetic resonance spectroscopy. We were able to nondestructively decode a bitmap image (192 bits) encoded using a library of 12 equimolar mixtures of an 8-bit-storing oMP and oLG, synthesized through semiautomated flow chemistry in less than 1% of the reaction time required for the repetition of conventional batch reactions. Our results highlight the potential of bundles of sequence-defined oligomers as efficient media for encoding and decoding large-scale information based on the automation of their synthesis and nondestructive sequencing processes.

Progresses in synthetic technology development for the production of L-lactide

L-Lactide is an intermediate for the industrial production of polylactic acid (PLA). The chemical and optical purities of lactide determine the quality of the prepared PLA. It is of great challenge to synthesize L-lactide efficiently with high chemical and optical purities under the conditions applicable for industrial production. With the national plastic reduction order issued, developing biodegradable materials such as PLA has gradually become a hot topic, and the production of upstream lactide is the key technique for the whole industrial chain. This mini-review aims to summarize typical works on the related synthetic technology development in recent years.

Surface Modification of Poly(lactic acid) Film via Cold Plasma Assisted Grafting of Fumaric and Ascorbic Acid

Plant-based materials have found their application in the packaging with a yearly growing production rate. These naturally biodegradable polymers are obtained from renewable and sustainable natural resources with reduced environmental impact and affordable cost. These materials have found their utilization in fully-renewable plant-based packaging products, such as Tetra Pak^®-like containers, by replacing commonly-used polyethylene as the polymer component. Poly(lactic acid) (PLA) is one of the representative plant-based polymers because of its eco-friendliness and excellent chemical and mechanical properties. In this work, a PLA surface was modified by various food additives, namely ascorbic acid (ASA) and fumaric acid (FA), using plasma-initiated grafting reactions in order to improve the surface and adhesion properties of PLA. Various analytical and microscopic techniques were employed to prove the grafting process. Moreover, the improved adhesion of the modified PLA foil to aluminum (Al) foil in a laminate configuration was proven by peel resistance measurements. The peel resistance of modified PLA increased by 74% and 184% for samples modified by ASA and FA, respectively, compared with untreated PLA.

A study on highly concentrated lactic acid and the synthesis of lactide from its solution

Lactic acid is an important platform compound used as raw material for the production of lactide and polylactic acid. However, its concentration and composition distribution are not as simple as those of common compounds. In this work, the mass concentration distribution of highly concentrated lactic acid is determined by back titration. The components of highly concentrated lactic acid, crude lactide, and polymer after the reaction are analyzed by HPLC. Different concentrations of lactic acid solution were prepared for the synthesis of lactide and its content in the product was determined by 1H NMR analysis. We found that lactide is more easily produced from high-concentration lactic acid solution with which the condensed water is easier to release. Hence, the removal of condensed water is crucial to the formation of lactide, although it is not directly formed by esterification of two molecules of lactic acid.

On the Optical Activity of Poly(L-Lactic Acid) (PLLA) Oligomers and Polymer: Detection of Multiple Cotton Effect on Thin PLLA Solid Film Loaded with Two Dyes

Optical rotatory dispersion (ORD) is a beautiful analytical technique for the study of chiral molecules and polymers. In this study, ORD was applied successfully to follow the degree of polycondensation of l-(+)-lactic acid toward the formation of poly(lactic acid) oligomers (PLAO) and high molecular weight poly(L-lactic acid) (PLLA) in a simple esterification reaction equipment. PLLA is a biodegradable polymer obtainable from renewable raw materials. The racemization of the intrinsically isotactic PLLA through thermal treatment can be easily followed through the use of ORD spectroscopy. Organic or molecular electronics is a hot topic dealing with the combination of π-conjugated organic compounds and polymers with specific properties (e.g., chirality) which can be exploited to construct optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic photovoltaic (OPV) high efficiency cells, switchable chirality devices, organic field-effect transistors (OFETs), and so on. ORD spectroscopy was applied to study either the gigantic optical rotation of PLLA films, as well as to detect successfully the excitonic coupling, occurring in thin solid PLLA green film loaded with a combination of two dyes: SY96 (a pyrazolone dye) and PB16 (the metal-free phthalocyanine pigment). The latter compound PLLA loaded with SY96 and PB16 shows a really gigantic optical activity in addition to typical ORD signal due to exciton coupling and may be considered as a simple and easily accessible model composite of a chiral polymer matrix combined with π-conjugated dyes for molecular electronics studies.