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Introduction to Polylactic Acid (PLA) Composites
Published in Jyotishkumar Parameswaranpillai, Suchart Siengchin, Nisa V. Salim, Jinu Jacob George, Aiswarya Poulose, Polylactic Acid-Based Nanocellulose and Cellulose Composites, 2022
Georg Graninger, Brian G. Falzon, Sandeep Kumar
Looking at bio-composites manufactured from CNFs and PLA, pristine CNFs can be introduced as direct reinforcement into the PLA matrix, causing an increase in strength and elastic modulus. The reinforcing effect is attributed to the long, flexible chains of CNF, offering high aspect ratios for enhanced stress transfer at the interface from PLA to the CNF reinforcement. While PLA is non-polar, CNFs and CNCs both have a polar nature. Consequently, only weak compatibility is enabled between the hydrophobic matrix and the hydrophilic fillers (Kargarzadeh, 2018). This, in turn, results in low loading levels with an optimal concentration of only about 0.5–2 wt.%. Wang et al. presented an approach combining microencapsulation-mixing and melt-compression to manufacture hydrophobic PLA containing high loading levels (8–32 wt.%). In addition to a large increase in modulus and strength of up to 58% and 210%, respectively, CNFs acting as nucleating agents cause positive changes in the crystallization behavior of the matrix (homogeneous and stable crystals, faster crystallization rate and lower cold crystallization temperature) (Song, 2013; Wang, 2012). A high loading of 17 wt.% was also achieved by Tingaut et al. when applying surface acetylation to modify CNFs. This promoted improved compatibility in the CNF-PLA composites, resulting in an increased glass transition temperature (Tg) (Tingaut, 2009). In comparison to CNFs, CNCs with their rod- or whisker-like shape are shorter and more rigid, causing agglomeration of CNCs in the PLA matrix and more brittle behavior. Therefore, physical (adsorption of a surfactant) and chemical (small molecule modification, grafting of PLA) surface modifications of CNC are required (Kargarzadeh, 2018; Zhou, 2021). The use of surfactant-modified CNCs in PLA has been reported to improve dispersion as well as increase thermal stability resulting in higher storage modulus at elevated temperatures in comparison to pristine CNC-PLA blends (Kvien, 2005; Petersson, 2007). Small molecule modification is performed to promote the hydrophobicity of cellulose. Three different chemical reaction types are most commonly used to apply this technique, during which hydrophilic hydroxyl groups on the cellulose surface are replaced by small molecules. Esterification, oxidation/amidation and silanization are three diverse chemical reactions that can be performed in facile reaction conditions. The advantage of this technique includes high grafting efficiency as well as the possibility to further modify the cellulose via optional functional groups. Fischer esterification (acylating agents: carboxylic acid (acid anhydride) under strong acid catalysis) and Steglich esterification (acylation catalyst: 4-dimethylaminopyridine [DMAP]) are two methods to esterify cellulose (acylation of hydroxyl groups). Depending on the small molecule substitute, three kinds of acid can be used for this procedure: mono-carboxylic acid (fatty/aromatic acid), lactic acid and multiple carboxylic acids (maleic/succinic anhydride) (Zhou, 2021).
Experimental and computational studies of laterally ethoxy Schiff base-ester liquid crystalline magnets
Published in Liquid Crystals, 2022
Wei-Jing Teoh, Nur Amanina Juniasari Tun Nur Iskandar, Guan-Yeow Yeap, Kazuyoshi Kaneko, Akio Shimizu, Masato M. Ito
The synthesis of 2-ethoxy-4-(((4-substituted phenyl)imino)methyl)phenyl-4’-(alkyloxy)-[1,1’-biphenyl]-4-carboxylate, 2a–2e, was carried out following the procedure as shown in Scheme 1. 2-Ethoxy-4-formylphenyl-4’-(alkyloxy)-[1,1’-biphenyl]-4-carboxylate, 1, will be prepared from the reaction between 4’-alkoxy-4-biphenylcarboxylic acid and 3-ethoxy-4-hydroxybenxaldehyde under Steglich esterification conditions using 4-dimethyl-aminopyridine (DMAP) and N,N’-dicyclohexylcarbodiimide (DCC) to form 1a and 1b. The desirable target compounds 2a-2 f were obtained by condensation between compounds 1a and 1b with the corresponding substituted anilines. Since the characteristics for compounds 2a–2e are identical, we will focus on the detailed discussion using compound 2a.
Synthesis and study the liquid crystalline behaviors of double Schiff bases bearing ester linkage as a central core
Published in Liquid Crystals, 2022
Mazin M. Abdul Razzaq Al-Obaidy, Ivan Hameed R. Tomi, Abdulqader M. Abdulqader
The final step in Scheme 1 conducted by condensation the compounds (Bn) with (Cx) using the Steglich esterification method in the presence of DMAP as a catalyst and DCC as a condensation agent in dry dichloromethane at room temperature to obtain the final esters (Dn) and (En) with yields in about 47–60%. The chemical structure of these compounds was identified by FT-IR, 1H and 13C-NMR; also, their chemical compositions were checked by elemental analysis. The FT-IR spectra show a strong sharp stretching peak between 1718 and 1737 cm−1 that refer to a (C=O) group for the ester compounds in the derivatives (Dn) and (En), also the FT-IR charts. Figure S1 shows an obvious increase in the extent of (C-H) stretching bands. These signals were clear evidence for a successful coupling reaction between compounds (Bn) and (Cx). Furthermore, The (1H) nuclear magnetic resonance spectrum of these series showed a presence of two singlet signals corresponding to the two imine groups, the new doublet of doublet signals for aromatic protons of new benzene rings and the signals of aliphatic protons corresponding to alkoxy chains in the tail of these derivatives (Dn) and (En). In addition to the above results, the obtained results of the elemental analyses and 13C-NMR signals were good provident to elucidate the chemical structure of these esters (see experimental part). Figure S2 shows some examples of 1H-NMR and 13C-NMR spectra for the final products.
Phase behaviour and magnetocaloric effect of poly(propylene imine) Iron(III) dendromesogen of the third generation
Published in Liquid Crystals, 2021
V.V. Korolev, M.S. Gruzdev, A.G. Ramazanova, O.V. Balmasova, U.V. Chervonova
Dendrimer, 3,4-bis-(decyloxybenzoyl) poly(propylene imine) derivative, as a ligand, was synthesised earlier [38]. At the first stage, N-hydroxysuccinimide ester with 3,4-didecyloxybenzoic acid was synthesised by Steglich esterification. The reaction of N-hydroxysuccinimide ester with primary amino-groups of dendrimer to introduction of 3,4-bis-(decyloxybenzoyl) fragments was used. NH2-groups on periphery of dendritic macromolecule are easy and selectively acidated by N-hydroxysuccinimide ester in the presence of triethylamine. Previously, this methodology was used successfully to the introduction of ferrocene fragments into analogue of protein – dendrimer of polyamidoamine of the fourth generation [39,40]. The synthetic pathway of the Fe(III) complex (Figure 1) with the third-generation dendrimer, 3,4-n-dodecyloxybenzoyl poly(propylene imine) derivative (3-K2.10), as the organic ligand, the structure and property investigations are described below.