Synthesis and characterization of new shellac–hydroxypropylmethylcellulose composite for pharmaceutical applications

Hydrogels formed with shellac and zein: pH-responsiveness, rheology, and gelation mechanism

Hydrogels responsive to pH have unique applications. Shellac is a pH-responsive molecule soluble above pH 7 but insoluble in acidic conditions. However, shellac-based hydrogels responding to pH have not been reported. In this study, 0.50-4.0 % w/v zein was incorporated in 4 % w/v shellac solutions to form hydrogels during pH-shifting from 12.0 to 6.2-6.4 enabled by gradual and uniform acidification due to hydrolysis of glucono-δ-lactone. These hydrogels maintained their volume when immersed in phosphate buffer at pH 7.0 but shrank at pH 6.0 and 6.5 and swelled or dissolved at pH 7.5 and 8.0. Increasing zein concentration led to greater changes in the hydrogel volume responding to pH changes. An increase in zein concentration facilitated gelation but excess zein weakened the network according to dynamic rheological tests and texture profile analyses. Molecularly, the alkaline pH led to multiple shellac molecules covalently bonded with zein according to gel electrophoresis. Analyses of hydrogel volume changes responding to NaCl, sodium dodecyl sulfate, and urea revealed the primary role of hydrophobic interaction and the secondary role of hydrogel bonds in forming hydrogels. These hydrogels with pH-responsiveness around pH 7.0 may find novel food and non-food applications.

Structure-property relationships in shellac-coated paper: impact of coating parameters on high-barrier bio-based packaging applications

Paper coated with bio-based materials has attracted significant interest as an alternative to plastic-based materials for food packaging, with poor moisture barrier of coated paper posing a challenge to broader applications. Shellac is a promising biopolymer because of its low cost, biodegradability, and wide approval as a food additive and food contact material. In this work, we have systematically studied the role of shellac concentration in butanol and the number of coatings on coated paper's moisture and oil barrier properties. We investigated surface, physicochemical, and thermal properties of coated paper to elucidate specific interactions between shellac and paper substrate and characterize coating morphology, and their effect on barrier properties of coated paper. We found that every layer of coating resulted in an improvement in surface properties, with porosity decreasing by 90 % and surface roughness decreasing by 80 % in a single coat of 15 % (w/w) shellac solution. A low concentration of shellac (7.5 % (w/w)) was found to be less effective in improving barrier properties compared to the highest shellac concentration of 15 % (w/w) used in our study, but still caused a significant increase in the GSM (change in coated weight (g.m-2)). Four coatings of the 15 % (w/w) shellac solution resulted in a water vapor transmittance rate (WVTR) of 56 g m-2 day-1, a water barrier (COBB 180) of 1 g m-2, and an oil barrier (KIT) of 12. These results meet the strictest requirements for very high-barrier packaging applications.

The Characterization of Natural Resins and a Study of Their Degradation in Interactions with Zinc Oxide Pigment

In the last few years, the role of science in Cultural Heritage has assumed greater significance since diagnostics have become essential for the characterization of artworks. The development of conservation strategies involves growing the study of artworks and the knowledge of the materials used against the degradation plaguing the painted surfaces. This work focuses on the investigation of the degradation processes involving paintings on canvas, in particular delamination and progressive deterioration of the painted surfaces. The main causes of the degradation are attributable to the formation of metal soaps, which originate from the interaction between binders and pigments; as a result, the process leads to the progressive fracturing of the paint film. Using various characterization techniques allowed us to acquire information on the structural and morphological properties of the binder resins and study the binder/pigment interaction during the degradation process to understand the quantity and quality of the acid sites present in the binders and, consequently, the potential reactivity with the cationic part of the pigments. The binders were also analyzed within paint layers in contact with zinc oxide to study the interactions and the possible formation of new species as metal soaps and metal oxalates that can modify the boundary among the painting layers and, consequently, the appearance of the artwork and its artistic value. Modifications after UV and thermal aging processes were observed using Infrared spectroscopy and thermogravimetric analysis. Zinc soap formation was observed after 7 h of a UV aging process and was correlated to the acidity of the resins.

Thermal crosslinking kinetics of shellac and its coating for stiffened and water stable cellulose-based paper straws

In this work, shellac and its crosslinking were studied to produce paper straws for the application of liquid products. Commercial paper straws are not durable for liquid foods due to their hygroscopic nature, and thus, they find it challenging to replace single-use plastics. Shellac is a naturally occurring resin utilized as an adhesive and water-resistant coating over the paper straw. Shellac was cured at 125 °C, 150 °C, 175 °C, and 200 °C, and it was crosslinked in about 210 min, 150 min, 60 min, and 30 min respectively and studied for kinetics. The crosslinking of shellac produced a thermally stable material. Compared to commercial paper straws, these paper shellac straws exhibited high bending stiffness (1356.11 Nmm), tensile strength (13,74 MPa), flexural strength (21.72 MPa), and compression strength (24.99 MPa). Moreover, the paper shellac straws didn't bend in wet conditions under load for up to one day, while the commercial paper straw bends in 8 min. Therefore, paper straws with shellac can replace plastic-based straws for a sustainable future.

Physicochemical and thermal characterization of the edible shellac films incorporated with oleic acid to enhance flexibility, water barrier and retard aging

In this work, shellac plasticized with oleic acid was solvent cast to prepare the flexible and water-resistant film for packaging applications. The films were prepared with varying amounts of oleic acid and studied in detail for appearance, surface morphology, thermal, chemical, barrier, mechanical, and robustness. The surface morphology confirmed the smooth surface of films up to SH-OA20 (100:20 w/w; shellac: oleic acid). Fourier-transform infrared spectroscopy confirmed that oleic acid reduced the hydrogen bonding of the shellac matrix to provide a plasticization effect. Also, the thermal analysis showed a reduction in the melting enthalpy. Moreover, the plasticized films had a better barrier to water vapor due to increased smoothness and reduction in brittleness. Adding oleic acid also increased the elongation at break up to 40 % without any changes in tensile strength. The flexibility of the films increased with the oleic acid content, making them resistant to burst, crumbling, bending, rolling, and stretching. Oleic acid also showed the retardation of aging and thermal aging of shellac. In the future, the long-term stability and migration of the films can be investigated.

Synergistic amalgamation of shellac with self-antibacterial hydroxyapatite and carboxymethyl cellulose: An interactive wound dressing for ensuring safety and efficacy in preliminary in vivo studies

This study focuses on the synergistic formulation of environmentally friendly blended materials based on carboxymethyl cellulose (CMC) for advanced interactive wound dressing. New CMC hydrogels were prepared with two degrees of functionalization and chemically crosslinked with citric acid (CA) to fine-tune their properties. Additionally, CMC-based hybrids were created by blending with shellac (SHL) and incorporating self-antibacterial hydroxyapatite (HA) to inhibit bacterial growth and promote wound healing. The results demonstrate the successful production of superabsorbent hydrogels with typical swelling degrees ranging from 81% in water to 82% in phosphate-buffered saline (PBS). These hydrogels exhibit distinct morphological features and remarkable improvements in surface mechanical properties, specifically in their tensile properties, which show a significant increase from approximately 0.03 to 2.2 N/mm2 due to the formation of CMC-SHL-HA hybrid nanostructures. Furthermore, the cytocompatibility of these CMC-based hydrogels was investigated by assessing the in vitro cell viability responses of human skin fibroblasts. The results reveal the cell viability responses over 91%, indicating their biocompatibility with human cells. Moreover, the characteristics of surgical wounds were assessed before and after the application of the hydrogel on dogs, and no signs of infection were observed at any of the surgical sites post-surgery.

Multiscale Shellac-Based Delivery Systems: From Macro- to Nanoscale

Delivery systems play a crucial role in enhancing the activity of active substances; however, they require complex processing techniques and raw material design to achieve the desired properties. In this regard, raw materials that can be easily processed for different delivery systems are garnering attention. Among these raw materials, shellac, which is the only pharmaceutically used resin of animal origin, has been widely used in the development of various delivery systems owing to its pH responsiveness, biocompatibility, and degradability. Notably, shellac performs better on encapsulating hydrophobic active substances than other natural polymers, such as polysaccharides and proteins. In addition, specially designed shellac-based delivery systems can also be used for the codelivery of hydrophilic and hydrophobic active substances. Shellac is most widely used for oral administration, as shellac-based delivery systems can form a compact structure through hydrophobic interaction, protecting transported active substances from the harsh environment of the stomach to achieve targeted delivery in the small intestine or colon. In this review, the advantages of shellac in delivery systems are discussed in detail. Multiscale shellac-based delivery systems from the macroscale to nanoscale are comprehensively introduced, including matrix tablets, films, enteric coatings, hydrogels, microcapsules, microparticles (beads/spheres), nanoparticles, and nanofibers. Furthermore, the hotspots, deficiencies, and future perspectives of shellac-based delivery system development are also analyzed. We hoped this review will increase the understanding of shellac-based delivery systems and inspire their further development.

Manipulation of the Glass Transition Properties of a High-Solid System Made of Acrylic Acid-N,N'-Methylenebisacrylamide Copolymer Grafted on Hydroxypropyl Methyl Cellulose

Crosslinking of hydroxypropyl methyl cellulose (HPMC) and acrylic acid (AAc) was carried out at various compositions to develop a high-solid matrix with variable glass transition properties. The matrix was synthesized by the copolymerisation of two monomers, AAc and N,N′-methylenebisacrylamide (MBA) and their grafting onto HMPC. Potassium persulfate (K₂S₂O₈) was used to initiate the free radical polymerization reaction and tetramethylethylenediamine (TEMED) to accelerate radical polymerisation. Structural properties of the network were investigated with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), modulated differential scanning calorimetry (MDSC), small-deformation dynamic oscillation in-shear, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results show the formation of a cohesive macromolecular entity that is highly amorphous. There is a considerable manipulation of the rheological and calorimetric glass transition temperatures as a function of the amount of added acrylic acid, which is followed upon heating by an extensive rubbery plateau. Complementary TGA work demonstrates that the initial composition of all the HPMC-AAc networks is maintained up to 200 °C, an outcome that bodes well for applications of targeted bioactive compound delivery.