Dependence on Film Thickness of Guest-Induced c Perpendicular Orientation in PPO Films

For poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films exhibiting nanoporous-crystalline (NC) phases, c^ orientation (i.e., crystalline polymer chain axes being preferentially perpendicular to the film plane) is obtained by crystallization of amorphous films, as induced by sorption of suitable low-molecular-mass guest molecules. The occurrence of c^ orientation is relevant for applications of NC PPO films because it markedly increases film transparency as well as guest diffusivity. Surprisingly, we show that the known crystallization procedures lead to c^ oriented thick (50–300 μm) films and to unoriented thin (£20 μm) films. This absence of crystalline phase orientation for thin films is rationalized by fast guest sorption kinetics, which avoid co-crystallization in confined spaces and hence inhibit formation of flat-on lamellae. For thick films exhibiting c^ orientation, sigmoid kinetics of guest sorption and of thickening of PPO films are observed, with inflection points associated with guest-induced film plasticization. Corresponding crystallization kinetics are linear with time and show that co-crystal growth is poorly affected by film plasticization. An additional relevant result of this study is the linear relationship between WAXD crystallinity index and DSC melting enthalpy, which allows evaluation of melting enthalpy of the NC α form of PPO (DHmo = 42 ± 2 J/g).

The Mechanism of Improvement of Film Solubility: Design and Evaluation of Film Forming System with Terbinafine as a Model Drug

Purpose: Film forming system (FFS) combines the advantages of patch and gel, it is expected to replace small doses of topical administration in the future. This work targets the design and evaluation of HPC-acrylic FFS with different excipients in appearance, rheology and in vitro properties. Also, the reason of improving the solubility of terbinafine film was illustrated by melting enthalpy thermo analysis.Methods: In this work, we prepared 8 HPC-acrylic FFS samples with different excipients, and characterized the film forming solutions and films in appearance, rheological properties, drug crystallization and in vitro performance. Then used melting enthalpy thermo-analysis to explain the mechanism of improvement of film solubility.Results: According to appearance evaluation, the samples which had a small amount of plasticizer could achieve an uniform surface morphology. The XRD and DSC demonstrated HPC could maintain drug amorphous in films. Based on oscillation frequency sweep, short chain plasticizer tributyl citrate (TBC) leading to strong entanglement and hydrogen bonding among the molecules. In vitro release test showed FP1 had favorable release. And the melting enthalpy thermo-analysis explained why FP1 had favorable release. Conclusions: HPC acted as an effective crystallization inhibitor. TBC could lead stronger intermolecular hydrogen bonds. The poloxamer had favorite miscibility with HPC-acrylic FFS. The combination of MCT and poloxamer with HPC resulted in a high Terbinafine solubility.

On the Use of Infrared Thermography for the Estimation of Melting Enthalpy

A calorimetry method based on infrared thermography is showing promise for material screening, allowing the simultaneous detection of phase transitions of multiple samples at a time, hence enabling the establishment of phase diagrams in a record time. The working principle of this method is similar to the one of Differential Thermal Analysis. Therefore, this work aims at identifying if the melting enthalpy of materials could be estimated on the same basis using infrared thermography. In this work, the melting of six eutectic mixtures of fatty acids is estimated under three considerations. The results are compared to Differential Scanning Calorimetry measurements and literature data. The accuracy of the method is discussed and improvements are proposed.

Fabrication of thermo-regulating cotton fabric with enhanced flame retardancy via layer-by-layer assembly

The lack of thermo-regulation functionality and high flammability of cotton fabrics greatly restrict their application in high-performance fields. Herein, we report a versatile layer-by-layer (LbL) assembly strategy for introducing to cotton fabrics a multilayered coating consisted of phase change microcapsules and ammonium polyphosphate, endowing them with thermo-regulating and flame retardancy. The coated fabrics were characterized by limiting oxygen index (LOI), scanning electron microscopy (SEM), thermogravimetry (TG), differential scanning calorimetry (DSC) and infrared thermal imaging. The fabric deposited with 20 bilayers (MCPM/APP-20) showed improved flame retardancy with a LOI of 24.4% and residual carbon of 34.24%. It also shows a melting enthalpy of 30.16 J/g, which transferred to a temperature difference of 6.4 ℃ compared with pristine cotton. The functional endowed by the LbL assembly was reasonably durable, with melting enthalpy and residual carbon of MPCM/APP-20 reduced to 17.14 J/g and 19.82% after 30 laundering cycles. These results suggest that LbL assembly was a convenient way for functionalization of cotton fabrics.

Poly(L-lactide): Optimization of Melting Temperature and Melting Enthalpy

Twice recrystallized L-lactide was polymerized with a dozen of different tin or bismuth catalysts in bulk at 160°C for 24 h and was annealed at 150°C afterwards. In two cases...

Determining the Composition of Imported Recycled Plastics with Differential Scanning Calorimetry

The analysis of the composition of recycled plastics is the prerequisite for identifying the properties of recycled plastics goods-solid waste. This paper systematically studies the composition of crystalline polymers by differential scanning calorimetry, and studies the common blends of polyethylene and polypropylene. The composition of polyamide 6 and polyamide 66 blends, polyethylene and polyamide blends and other common recycled plastics. The standard enthalpy value method and the melting enthalpy area normalization method are compared. The conclusion is that the melting enthalpy area normalization method is more beneficial Determine the composition of recycled plastics. For polyethylene/polypropylene blends, the repeatability of polyethylene and polypropylene should not exceed 5%; for polyamide 6/polyamide 66 blends, the repeatability of polyamide should not exceed 5%. More than 3%; For blends of polyethylene and polyamide, the repeatability of polyethylene and polyamide should not exceed 6%.

Design of Deep Eutectic Systems: A Simple Approach for Preselecting Eutectic Mixture Constituents

Eutectic systems offer a wide range of new (green) designer solvents for diverse applications. However, due to the large pool of possible compounds, selecting compounds that form eutectic systems is not straightforward. In this study, a simple approach for preselecting possible candidates from a pool of substances sharing the same chemical functionality was presented. First, the melting entropy of single compounds was correlated with their molecular structure to calculate their melting enthalpy. Subsequently, the eutectic temperature of the screened binary systems was qualitatively predicted, and the systems were ordered according to the depth of the eutectic temperature. The approach was demonstrated for six hydrophobic eutectic systems composed of L-menthol and monocarboxylic acids with linear and cyclic structures. It was found that the melting entropy of compounds sharing the same functionality could be well correlated with their molecular structures. As a result, when the two acids had a similar melting temperature, the melting enthalpy of a rigid acid was found to be lower than that of a flexible acid. It was demonstrated that compounds with more rigid molecular structures could form deeper eutectics. The proposed approach could decrease the experimental efforts required to design deep eutectic solvents, particularly when the melting enthalpy of pure components is not available.