434 research outputs found
Talc concentration effect on shelf life of acetaminophen tablets
Excipients in pharmaceutical formulations are inactive ingredient from the biological point of view, but they have a key role in the preparation, and they can alter the stability of the active principle. In this work, we prepared acetaminophen tablets with different amounts of talc as excipient and the thermal stability was deeply investigated by thermogravimetric studies. Isoconversional analysis by Kissinger–Akahira–Sunose method and “Master plot” analysis have been successfully employed to describe the kinetics of degradation under inert atmosphere, and the shelf lives have been calculated as a function of the talc content. The shelf-life values as well as the activation energy, which is the dominant factor, evidenced that the inorganic filler enhances the drug degradation to a certain extend and that the composition dependence has a peculiar trend reflecting the particle cluster formation at a critical concentration value. An effort of physico-chemical explanation for this behaviour is put forward by a simple geometrical model from the microparticle-size analysis to predict the critical talc concentration
Safely dissolvable and healable active packaging films based on alginate and pectin
Extensive usage of long-lasting petroleum based plastics for short-lived application such as packaging has raised concerns regarding their role in environmental pollution. In this research, we have developed active, healable, and safely dissolvable alginate-pectin based biocomposites that have potential applications in food packaging. The morphological study revealed the rough surface of these biocomposite films. Tensile properties indicated that the fabricated samples have mechanical properties in the range of commercially available packaging films while possessing excellent healing effciency. Biocomposite films exhibited higher hydrophobicity properties compared to neat alginate films. Thermal analysis indicated that crosslinked biocomposite samples possess higher thermal stability in temperatures below 120 °C, while antibacterial analysis against E. coli and S. aureus revealed the antibacterial properties of the prepared samples against different bacteria. The fabricated biodegradable multi-functional biocomposite films possess various imperative properties, making them ideal for utilization as packaging material
Preparation of palladated porous nitrogen-doped carbon using halloysite as porogen: disclosing its utility as a hydrogenation catalyst
In this article, halloysite nanoclay (Hal) was used as porogen for the synthesis of nitrogen doped porous carbon material with high specific surface area and pore volume. To this purpose, polymerization of melamine and terephthalaldehyde (MT) was performed in the presence of amine-functionalized carbon coated Hal (Hal@Glu-2N) that was prepared from hydrothermal treatment of Hal and glucose. Then, the prepared nanocomposite was palladated and carbonized to afford Pd@Hal@C. To further improve the textural properties of the nanocomposite, and introduce more pores in its structure, Hal nanotubes were etched. The characterization of the resulting compound, Pd@C, and comparing it with Pd@Hal@C, showed that etching of Hal significantly increased the specific surface area and pore volume in Pd@C. Pd@C was successfully used as a heterogeneous catalyst for promoting hydrogenation of nitroarens in aqueous media using hydrogen with atmospheric pressure as a reducing agent. The comparison of the structural features and catalytic activity of the catalyst with some control catalysts, including, Pd@Hal, Pd@Hal@Glu, Pd@Hal@Glu-MT and Pd@Hal@C confirmed that nitrogen groups in C could improve the Pd anchoring and suppress its leaching, while etching of Hal and introduction of more pores could enhance the catalytic activity through facilitating the mass transfer
Thermal and mechanical properties of polycaprolactone-based composites with diatomaceous earth and halloysite nanotubes
1. Introduction
The biodegradable polymers have been attracted interest for the design of green composites in recent decades to face the urgent environmental issues.
Polycaprolactone (PCL) is one of the most promising environmentally friendly polymers. Recent studies have reported that blending PCL with different types of fillers may affect its physic-chemical properties and crystallization rate.
Halloysite nanotubes (HNT) and diatomaceous earth (DE) have been recently investigated for the preparation of PCL-based composites with appealing performances1,2. Both are naturally occurring materials with nanoscale dimensions and a structure that lend them also absorbent properties. Potentialities of such materials in polymer composites need to be further developed for environmental remediation applications3.
For the study, binary blends of PCL with HNT and DE were prepared by melt mixing, starting from 5 w/t% of filler to the maximum miscible concentration to the polymer. The thermal and mechanical properties of the obtained composites were investigated. Thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical analysis were employed for the research purposes.
2. Results and Discussion
Thermogravimetric analysis (TGA): The measurements were carried out by using the Q5000 IR instrument (TA Instruments) under nitrogen flow of 25 cm3/min by heating the samples from 20° to 800 °C. with a rate of 1°C/min. The degradation temperature of the pristine materials and their composites were taken at the maximum of the first order derivative curves of mass percentage vs. temperature.
It was observed that concentration of HNTs up to 15 w/t% did not affect the thermal stability of PCL. The recorded Tmax values show no significant variations compared to pristine PCL. Higher content of HNT, beyond these levels, leads to a significative decrease in the thermal stability of the PCL matrix, resulted in a lower onset decomposition temperature.
The addition of DE did not significatively affect the thermal stability of the composites, with a similar onset temperature for all of composites as the DE content increased.
Graphs of the residue vs filler concentration showed a good dispersion degree of the filler particles throughout the polymeric matrix.
Differential scanning calorimetry (DSC): The melting and crystallization behaviour testing of the composites and of pristine materials were carried out by using the differential scanning calorimeter TA Instrument DSC (2920 CE). Samples of approximately 5 mg were heated from 25°C to 80°C at a rate of 1 °C/min, under nitrogen atmosphere. The melting temperatures at the onset (Tmi), at the peak (Tmp) and the enthalpy of melting (ΔHm) per gram of PCL in the composites were calculated.
The heating thermograms showed melting temperatures values constant for both PCL-based composites as compared to the neat PCL. The crystallinity degree (ę“c) of PCL did not change for blends with DE while significant variations were observed in PCL/HNT nanocomposites. The results showed that, up to the filler concentration of 15 wt%, ę“c increase, indicating that the well-dispersed HNT acted as nucleating agents in the PCL matrix. At higher concentrations, the crystallinity degree decreased, affected by the achievement of the percolation threshold of HNT and by the consequent decrease in molecular mobility of the PCL chains in the nanocomposites.
Dynamic mechanical analysis (DMA): Dynamic mechanical measurements were performed by using the DMA Q800 (TA Instruments). The temperature range was 30° to 80°C with a scan rate of 2°C/min, at an applied oscillation frequency of 1 Hz and strain of 0.5%. The shear gear method with samples of a surface of 100 mm2 were employed to measure the elastic (storage modulus) and the viscous (loss modulus) components and tan delta parameters. For the study, the peak maximum of the loss modulus curves was considered. It was observed that these values reduced in the filled system as compared to the pristine counter parts, which is due to the reduction of viscous component of the polymer matrix by the presence of HNT and DE.
3. Conclusions
Well-dispersed binary blends of PCL with HNT and DE were prepared by melt mixing. Composites with the maximum miscible concentration to the polymer were obtained since there is a lack of information in the literature on the evolution of crystallization rate in PCL composites containing high percentages of fillers.
TGA and DSC analysis evidenced that the thermal properties of the polymer are mostly affected by the HNT addition and that the HNT concentration of 15 w/t% represents a sort of critical threshold after which a change in the behaviour of the composites occurs.
Viscoelastic measurements showed that both fillers increase the capacity of PCL to store energy during mechanical stress as their content percentage increases.
The reported data are the result of a preliminary characterization of sustainable composites whose potential for environmental remediation applications is currently being studied.
References
1. Kassa, A.,et al. Effects of montmorillonite, sepiolite, and halloysite clays on the morphology and properties of polycaprolactone bionanocomposites. Polym.Compos. 28(2020)
2. Oun, A. A.,et al. Comparative study of oregano essential oil encapsulated in halloysite nanotubes and diatomaceous earth as antimicrobial and antioxidant composites. Appl. Clay Sci. 224(2022)
3. Cavallaro, G.,et al. Organic-nanoclay composite materials as removal agents for environmental decontamination. RSC Adv. 9(2019
A review on biopolymer-based treatments for consolidation and surface protection of cultural heritage materials
Nowadays, the scientific community emphasizes the use of reversible and non-toxic materials in the field of cultural heritage. Biopolymers are one of the alternative materials to synthetic polymers and solvents that are dangerous for human health and for the environment, applied in consolidation and coating treatment. Natural biopolymers may be divided into polysaccharide, protein, and polyester: All of them are low cost, eco-friendly, and biocompatible, besides many physicochemical characteristics such as being transparent, soluble in water, hydrogel, and film-forming, and can be easily functionalized. The addition of nanoclay, essential oil, and active molecules improves the physicochemical properties of biopolymers and proposes smart response abilities to the new composite material. This work is intended to provide an overview of the development of biopolymers by considering the most general aspects and scanning the diverse substrates of application for the conservation and protection of cultural heritage. Graphical abstract: [Figure not available: see fulltext.
Thermal and Mechanical Characterization of Yarn Samples from Flemish Tapestry of the Sixteenth Century
We propose a physico-chemical approach for theharacterization of the conservation condition of yarns from a Flemish tapestry of the sixteenth century. The aging effect on the yarns' performance was evaluated by comparison with commercial materials. Water uptake experiments highlighted the aptitude of yarns toward water sorption and their increased hydrophilicity upon aging. Thermogravimetric analysis can be considered a fast approach for the fiber identification and assessment on the material life-time. The dynamic mechanical analysis provided direct evidence on the yarns, conservation state and their performance under different mechanical stresses. The proposed characterization path can be relevant for stating the condition of the tapestry and for designing a conservation protocol for the preservation of the artwork
Covalently modified halloysite clay nanotubes: synthesis, properties, biological and medical applications
Halloysite (HNT) is a promising natural nanosized tubular clay mineral that has many important uses in different industrial fields. It is naturally occurring, biocompatible, and available in thousands of tons at low cost. As a consequence of a hollow cavity, HNT is mainly used as nanocontainer for the controlled release of several chemicals. Chemical modification of both surfaces (inner lumen and outer surface) is a strategy to tune the nanotube's properties. Specifically, chemical modification of HNT surfaces generates a nanoarchitecture with targeted affinity through outer surface functionalization and drug transport ability from functionalization of the nanotube lumen. The primary focus of this review is the research of modified halloysite nanotubes and their applications in biological and medical fields
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