Effects of Chitosan and Cellulose Derivatives on Sodium Carboxymethyl Cellulose-Based Films: A Study of Rheological Properties of Film-Forming Solutions.

Bio-based packaging materials and efficient drug delivery systems have garnered attention in recent years. Among the soluble cellulose derivatives, carboxymethyl cellulose (CMC) stands out as a promising candidate due to its biocompatibility, biodegradability, and wide resources. However, CMC-based films have limited mechanical properties, which hinders their widespread application. This paper aims to address this issue by exploring the molecular interactions between CMC and various additives with different molecular structures, using the rheological method. The additives include O-carboxymethylated chitosan (O-CMCh), N-2-hydroxypropyl-3-trimethylammonium-O-carboxymethyl chitosan (HTCMCh), hydroxypropyltrimethyl ammonium chloride chitosan (HACC), cellulose nanocrystals (CNC), and cellulose nanofibers (CNF). By investigating the rheological properties of film-forming solutions, we aimed to elucidate the influencing mechanisms of the additives on CMC-based films at the molecular level. Various factors affecting rheological properties, such as molecular structure, additive concentration, and temperature, were examined. The results revealed that the interactions between CMC and the additives were dependent on the charge of the additives. Electrostatic interactions were observed for HACC and HTCMCh, while O-CMCh, CNC, and CNF primarily interacted through hydrogen bonds. Based on these rheological properties, several systems were selected to prepare the films, which exhibited excellent transparency, wettability, mechanical properties, biodegradability, and absence of cytotoxicity. The desirable characteristics of these selected films demonstrated the strong biocompatibility between CMC and chitosan and cellulose derivatives. This study offers insights into the preparation of CMC-based food packaging materials with specific properties.

Polyphosphazene-Functionalized Microspheres as Efficient Catalysts for the Knoevenagel Reaction under Mild Conditions.

Inspired by the formation of microspheres by hexachlorocyclotriphosphazene and 4, 4'-sulfonyldiphenol, polyphosphazene-functionalized microspheres were developed. Benefits from the supported supper basic phosphazene, the yield exceeded 99 % at room temperature in the manner of second-order reaction kinetics toward Knoevenagel reaction and was still maintained at 99 % after 16 runs. In the experimental temperature from 0 °C to 90 °C, the yield increased from 92 % to 99 %, reflecting that the catalyst had strong applicability under mild conditions. This behavior was conducive to energy conservation. Meanwhile, simple separation and recovery further enhanced this advantage. In addition, the catalyst was also found to be insensitive to aqueous solution or organic solvents such as toluene, THF, EtOH and CH3 CN. This property gave the Knoevenagel reaction a vast choice. All these features exhibit that this novel catalyst is an attractive and applicable alternative in organic synthesis.

Hofmeister effect on the viscosity properties of gelatin in dilute solutions.

The effect of various Hofmeister anions on the molecular conformation of gelatin in dilute solutions was investigated by viscosity, optical rotation and dynamic light scattering (DLS). The results showed that the intrinsic viscosity of gelatin decreased in the presence of the kosmotropic anions such as Citrate3-, SO42-, H2PO4- and MeCOO-, whereas it was increased with the addition of chaotropes such as Cl- and KSCN-. Furthermore, the intrinsic viscosity of gelatin was directly correlated to the hydration entropy of kosmotropic anions, suggesting that the decrease of the intrinsic viscosity was attributed to the strong hydration effect of kosmotropes. The strong dehydration of gelatin facilitated the folding of the polymer chains into helix bundles, validated by the results of optical rotation. On the contrary, the chaotropic anions could interact directly with polypeptide backbones, and the intrachain hydrogen bonds were destroyed. As a result, the polymer chains expanded, which was confirmed by DLS data, and the intrinsic viscosity was increased. These observations indicate that the molecular conformation of gelatin can be modulated by Hofmeister anions.

Solution properties of N-(2-allyl-butyl ether)-O-carboxymethyl chitosan and N-(2-allyl-isooctyl ether)-O-carboxymethyl chitosan.

pH-sensitive and amphiphilic chitosan derivatives can be used as hydrophobic drug carriers, and their rheological properties play a key role in their performance. In this paper, two pH-responsive and amphiphilic chitosan derivatives, N-(2-allyl-butyl glycidyl ether)-O-carboxymethyl chitosan (HBCC) and N-(2-ethylhexyl glycidyl ether)-O-carboxymethyl chitosan (H2ECC) were synthesized, and their rheological properties were studied. The influence of parameters including concentrations of HBCC and H2ECC, the degree of substitution, solution pH, and [Ca2+] on the rheological properties were investigated. The results showed that the overlap and entanglement concentration of HBCC and H2ECC was ca. 1.7 wt% and 5 wt%, respectively. The dilute and semidilute solutions showed Newtonian behavior. Above 5 wt%, strong networks formed, and shear-thinning behavior appeared at high shear rates (>10 s-1) for entangled solutions. A high degree of substitution and pH near the isoelectric points of HBCC and H2ECC corresponded to a low viscosity and viscoelasticity. In addition, Ca2+ played a shielding effect on the -COO- groups at low concentrations (<10 mmol/L), whereas it acted as a cross-linker when [Ca2+] ≥ 20 mmol/L. The intermolecular hydrogen bonds were examined by molecular dynamics simulations. The results provide new information related to the application of HBCC and H2ECC for hydrophobic drug packaging and transportation.

Synthesis, structure, and properties of N-2-hydroxylpropyl-3-trimethylammonium-O-carboxymethyl chitosan derivatives.

N-2-hydroxylpropyl-3-trimethylammonium-O-carboxymethyl chitosan (HTCMCh) was synthesized through homogeneous reaction. The effects of different reaction condition on the properties of HTCMCh were characterized by FTIR, NMR, SEM, TEM, DLS, XRD, TGA, and DSC. The results of FTIR spectra, 1H NMR, and 13C NMR proved the successful synthesis of HTCMCh. The DS was dependent upon reaction time and pretreated pH of the starting material, independent of temperature and nepoxy/n-NH2. With increasing reaction time, the crystallinity of HTCMCh decreased, and the intermolecular interactions transformed from hydrogen bonding to strong electrostatic interactions, which enhanced HTCMCh thermal stability. SEM observations showed smooth cross section morphologies of HTCMCh films. With the increase in reaction time, the tensile strength significantly increased. The viscoelasticity transformed from viscous to elastic with aging time, confirming the formation of polyelectrolyte complexes. The optimum reaction conditions: reaction time of 2 h, an initial material pH of 9.47, nepoxy/n-NH2 of 2/1.

Structural characterization and properties of polyols plasticized chitosan films.

In this study, the influence of different polyols such as glycerol, xylitol and maltitol on the crystalline structure and thermal properties of chitosan films were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The concentration of polyol was fixed at 20 wt%. FTIR result showed that the addition of polyols weakened the hydrogen bonding between chitosan molecules, whereas the electrostatic interactions remained nearly unchanged. Structural analysis revealed that the plasticizer which promoted the crystallization of chitosan was moisture rather than polyol contained in the polymer films. DSC result indicated that glycerol plasticized film had a lower glass transition temperature (Tg) and lower melting temperature (Tm). The low thermal transition temperatures suggested that the moisture content is higher in glycerol plasticized film, which was evidenced by TGA result. In addition, the polyols incorporation resulted in a decrease of the tensile strength of chitosan films, while their ductility was improved. These observations indicate that the addition of polyols as plasticizers could regulate the microstructure as well as the properties of chitosan films, which is essential for their usage in food industry.

Molecular interactions in gelatin/chitosan composite films.

Gelatin and chitosan were mixed at different mass ratios in solution forms, and the rheological properties of these film-forming solutions, upon cooling, were studied. The results indicate that the significant interactions between gelatin and chitosan promote the formation of multiple complexes, reflected by an increase in the storage modulus of gelatin solution. Furthermore, these molecular interactions hinder the formation of gelatin networks, consequently decreasing the storage modulus of polymer gels. Both hydrogen bonds and electrostatic interactions are formed between gelatin and chitosan, as evidenced by the shift of the amide-II bands of polymers. X-ray patterns of composite films indicate that the contents of triple helices decrease with increasing chitosan content. Only one glass transition temperature (Tg) was observed in composite films with different composition ratios, and it decreases gradually with an increase in chitosan proportion, indicating that gelatin and chitosan have good miscibility and form a wide range of blends.

Effect of anionic surfactants on grafting density of gelatin modified with PDMS-E.

The effect of anionic surfactants on the interfacial compatibility in mono epoxy terminated polydimethylsiloxane (PDMS-E) macromonomer and gelatin mixed system was studied by Gibbs free energy (ΔGM), which played a crucial role in deciding the grafting density of immiscible polymer in heterogeneous system. Aggregation behavior of gelatin chains at boundary between gelatin phase and solvent phase was investigated using viscosity, surface tension and conductivity measurements. Viscosity analysis showed a regular increase in viscosity with the increasing alkyl chain length from C7 to C16 of the homologous alkyl sulfate surfactants. Changes of surface tension exhibited the regular curves of polyelectrolyte-anionic surfactant for alkyl sulfate surfactant systems. The results demonstrated that aggregate structure of gelatin-sulfate surfactants was dominated by electrostatic and hydrophobic interactions, which resulted in a self-assembly process of the hydrophobic segments and hydrophilic segments among gelatin chains and surfactant molecules. However, the interactions between gelatin and alkyl sulfonate surfactants were mainly governed by hydrophobic interactions, which induced conformation change of gelatin molecules. Well-ordered arrangement of gelatin chains at a fluid interface has observed by high-resolution transmission electron microscopy (HR-TEM). It is a key factor to contribute to the reduction of interfacial free energy, which mainly depends on the hydrophobic interaction between gelatin and alkyl sulfate/sulfonate surfactants. MD simulations conclusions are great agreement with our experimental results.

Solid-state structure of gelatin-mono epoxy terminated polydimethylsiloxane polymer: effect of electrostatic and hydrophobic interactions.

In this study, a hybrid synthetic gelatin-mono epoxy terminated polydimethylsiloxane polymer (PDMS-E grafted gelatin (PGG)) was successfully synthesized on a large scale. Supramolecular structure of gelatin, which was decided by the sophisticated inter- and intra-molecular interactions, significantly affected the self-assembly and phase behavior of PGG. Interestingly, the supramolecular organization of PGG could be tuned finely by negatively charged surfactants, such as sodium dodecyl sulfate (SDS) and sodium tetradecyl sulfonate (STSo), as revealed by high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), light microscopy (LM), and atomic force microscopy (AFM). SEM images exhibited the presence of spherical aggregates in PGG/SDS films while hexagonal array was observed in PGG/STSo films. The results of LM revealed that when PGG/STSo solution was dried, a successive structural transformation from spheres to hexagons, via sticks and butterfly-shaped aggregates as intermediates, was observed. However, the morphologies of the aggregates formed in PGG/SDS system did not exhibit any obvious change upon drying. Attenuated total reflection-Fourier transform infrared spectra combined with AFM observations indicated that the secondary structure and aggregation behavior of gelatin was modified with the change in the electrostatic and hydrophobic interactions, leading to the formation of diversified solid-state structures of PGG.

Microstructure transformation of PDMS-E grafted gelatin polymers induced by SDS and SDBS.

Inorganic-organic hybrid materials with tunable chemical and physical properties were prepared from mono epoxy terminated polydimethylsiloxane (PDMS) macromonomer and gelatin for improving their flexibility and hydrophobicity. Sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) were used to enhance the compatibility of two polymers phases. Measurement of grafting density indicated that anionic surfactants played a crucial role in deciding the detailed microstructure of PDMS-E grafted gelatin (PGG) polymers in alkaline solution. The interaction between gelatin and SDS/SDBS was investigated by viscosity and SEM. Viscosity analysis showed a regular increase in SDS system and a steeper change in the case of SDBS. SEM micrographs displayed a series of structural transitions (spherical, spindle, irregular granular and spherical aggregates) with the increase of SDS concentration, but spindle and granular aggregates appeared alternately as varying SDBS concentrations. The results demonstrated that both the electrostatic and hydrophobic interactions between anionic surfactant and gelatin controlled the aggregate structure of gelatin-SDS/SDBS, which affected the compatibility between gelatin and PDMS. Thermal properties of PGG polymers had changed with the modification of polymer microstructure. The results above revealed that microstructure transformation of PGG polymers was determined by the compatibility of two polymers in anionic surfactant aqueous solution and the chemical nature of their monomers.

Effect of aggregation behavior of gelatin in aqueous solution on the grafting density of gelatin modified with glycidol.

The effect of aggregation behavior of gelatin in aqueous solution on the grafting density of glycidol grafted gelatin polymers (GGG polymers) was investigated. The grafting density was measured using the Van Slyke method by calculating the conversion rate of free - NH(2) groups of gelatin. The conversion rate reached peak values at 6% and 14% of the gelatin aqueous solution. SEM micrographs displayed a series of structural transitions (i.e., spherical, spindle, butterfly, irregular and dendritic aggregates) at varying concentrations from 2% to 16% (w/w) at an interval of 2% (w/w). The spindle aggregates reappeared at the concentrations of 6% and 14%. Viscosity measurements indicated that the physicochemical properties of the gelatin solution had changed with increasing concentration. UV and CD analysis indicated that hydrophobic interactions competed with hydrogen bonding, and the random coils partly transformed to ß-sheet structure by changing the concentration. Zeta potential and pH data confirmed the increasing electrostatic repulsion associated with increasing the hydrophobic region. XPS analysis revealed that the elemental composition of the gelatin particle surface changed with variation in the aggregate structure, determining the monotonic variation of the grafting density with increasing concentration. Results demonstrate that aggregation behavior of gelatin in aqueous solution plays a crucial role in deciding the grafting density of gelatin modified products.