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

2021 ◽  
Vol 22 (5) ◽  
pp. 2682
Author(s):  
Nazim Nassar ◽  
Felicity Whitehead ◽  
Taghrid Istivan ◽  
Robert Shanks ◽  
Stefan Kasapis
Keyword(s):  
Glass Transition ◽  
Acrylic Acid ◽  
Methyl Cellulose ◽  
Small Deformation ◽  
Polymerization Reaction ◽  
Solid Matrix ◽  
Scanning Calorimetry ◽  
Modulated Differential Scanning Calorimetry ◽  
High Solid ◽  
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.

Evaluation of Potential Printed Wiring Board Materials: Thermoplastic Polyimide + Polymer Liquid Crystal Blends

1998 ◽  
Vol 515 ◽  
Author(s):  
Witold Brostow ◽  
Nandika Anne D'Souza ◽  
Bhaskar Gopalanarayanan ◽  
Elizabeth G. Jacobs
Keyword(s):  
Glass Transition ◽  
Elevated Temperatures ◽  
Moisture Absorption ◽  
Cold Crystallization ◽  
Printed Wiring Board ◽  
Scanning Calorimetry ◽  
Modulated Differential Scanning Calorimetry ◽  
Adhesion Properties ◽  
Polymer Liquid ◽  
Wiring Board

ABSTRACTPolymer liquid crystals (PLCs) have potential applications as printed wiring board materials and in other aspects of plastic packaging. They have a number of desirable properties such as low moisture absorption, thermoplastic behavior, and low thermal expansivity. However, PLCs can have significant anisotropy in expansivity with negative expansivities in the drawing or molding direction and relatively low positive expansivities in the transverse directions. By incorporating PLCs into an engineering polymer (EP) matrix, in our case a thermoplastic polyimide (TPI), we expected to be able to control the expansivity of the resulting blend – thereby aiding in long-term service performance and reliability. Properties such as low moisture absorption, dimensional stability at elevated temperatures, good adhesion properties, and reworkability were also sought. In this paper, we report on our work to process a TPI/PLC blend and characterize the thermal properties of the blends.An amorphous TPI was chosen over a semicrystalline one because of a thermo-irreversible cold crystallization in the latter, causing undesirable changes in the morphology and poor adhesion to metals. Our evaluations of TPIs through thermally stimulated depolarization (TSD) and temperature-modulated differential scanning calorimetry (TMDSC) reveal sub-glass transition relaxations. We have investigated the selected semicrystalline TPI + PLC pair in the entire composition range, and concluded that the narrower range, up to 30 wt. % of the PLC, is sufficient for the achievement of our objectives. The glass transition temperature Tg = 240°C of the TPI determined by DSC is unaffected by variations of the PLC concentration. The cold crystallization temperature of the semicrystalline TPI decreases with increasing PLC concentration but upon formation of the LC-rich islands this effect becomes smaller. All the blends exhibit degradation onset temperature over 520°C. The thermal conductivity of the amorphous TPI + PLC blends varies as a function of the PLC concentration. The blends show very good film formability. The addition of the PLC improves the processability of the TPI. Thermomechanical analysis (TMA) reveals that the desired control of the expansivity of the blends is also achieved by varying the PLC concentration.

Glass transformation in vitreous As2Se3 studied by conventional and temperature-modulated differential scanning calorimetry

2001 ◽  
Vol 16 (8) ◽  
pp. 2399-2407 ◽  
Author(s):  
S. O. Kasap ◽  
D. Tonchev
Keyword(s):  
Activation Energy ◽  
Differential Scanning Calorimetry ◽  
Relaxation Time ◽  
Glass Transition ◽  
Activation Energies ◽  
Temperature Modulation ◽  
Glass Transition Region ◽  
Scanning Calorimetry ◽  
Modulated Differential Scanning Calorimetry ◽  
Apparent Activation Energies

We have studied the glass transition behavior of vitreous As2Se3 by carrying out temperature-modulated differential scanning calorimetry (TMDSC) and conventional differential scanning calorimetry (DSC) experiments to measure the glass transition temperature Tg. In TMDSC experiments we have examined the reversing heat flow (RHF), that is the complex heat capacity CP in the glass transition region as the glass is cooled from a temperature above the glass transition temperature (from a liquidlike state) and also as the glass is heated starting from room temperature (from a solidlike state). The RHF, or CP versus T, in TMDSC changes sigmoidally through the glass transition region without evincing an enthalpic peak which is one of its distinct advantages for studying the glass transformations. The Tg measurements by TMDSC were unaffected by the amplitude of the temperature modulation. We have determined apparent activation energies by using Tg-shift methods based on the Tg-shift with the frequency (ω) of temperature modulation in the TMDSC mode and Tg-shift with heating and cooling rates, r and q, respectively, in the DSC mode. It is shown that the apparent activation energies ∆h* obtained from ln ω versus 1/Tg and ln q versus 1/Tg plots are not the same, but nonetheless, they are approximately the same as the apparent activation energy ∆hn of the viscosity over the same temperature range where the empirical Vogel expression of Henderson and Ast, η = 12.9 exp[2940/(T - 335)], was used for the viscosity. The latter observation is in agreement with the assertion that the structural relaxation time Ʈ is proportional to the viscosity h. The apparent activation energy ∆hr obtained from the ln r versus 1/Tg plot during heating DSC scans is lower than ∆h* observed during cooling scans. The results are discussed in terms of a phenomenological Narayanaswamy type relaxation time. It was observed that Tg obtained from TMDSC cooling experiments did not depend on the underlying cooling rate for q ≤ 1 °C min-1; and for temperature amplitudes 0.5–5 °C. The transition due to the temperature modulation was well separated from the transition due to the underlying cooling rate. Further, the apparent activation energies obtained from ln ω versus 1/Tg during cooling and heating scans for q and r ≤ 1 °C min−1 are approximately the same as expected from Hutchison's calculations using a single relaxation time model of TMDSC experiments.

Glass Formation During Room Temperature, Isothermal Drying

2003 ◽  
Author(s):  
Alptekin Aksan ◽  
Mehmet Toner
Keyword(s):  
Glass Transition ◽  
Glassy State ◽  
Glass Transitions ◽  
Scanning Calorimetry ◽  
Modulated Differential Scanning Calorimetry ◽  
Glass Transition Kinetics ◽  
The Stability ◽  
Isothermal Drying ◽  
Kinetics Of

Isothermal drying and glass transition of solutions and films have drawn considerable attention from many industries. We here explore the feasibility of modifying the isothermal drying and vitrification kinetics of carbohydrate solutions in order to ensure the stability and quality of their ingredients. Modulated Differential Scanning Calorimetry experiments with isothermally dried trehalose and trehalose/dextran solutions were performed and the glass transition kinetics have been determined. Three distinct drying regimes were observed. With isothermal, isobaric drying at 0%RH, it was indeed possible to reach the glassy state for a trehalose and a trehalosedextran system. With the addition of high molecular weight sugars, the glass transitions of isothermally dried carbohydrate solutions can be accelerated as a function of dextran mass ratio in the sample.

scholarly journals Commentary: Considerations in the Measurement of Glass Transition Temperatures of Pharmaceutical Amorphous Solids

2019 ◽  
Vol 21 (1) ◽  
Author(s):  
Ann Newman ◽  
George Zografi
Keyword(s):  
Glass Transition ◽  
Amorphous Solid ◽  
Amorphous Solids ◽  
Scanning Calorimetry ◽  
Modulated Differential Scanning Calorimetry ◽  
Preparation Methods ◽  
Glass Transition Temperatures ◽  
Pharmaceutical Applications ◽  
Sample Preparation Methods

AbstractAn increased interest in using amorphous solid forms in pharmaceutical applications to increase solubility, dissolution, and bioavailability has generated a need for better characterization of key properties, such as the glass transition (Tg) temperature. Although many laboratories measure and report this value, the details around these measurements are often vague or misunderstood. In this article, we attempt to highlight and compare various aspects of the two most common methods used to measure pharmaceutical Tg values, conventional and modulated differential scanning calorimetry (DSC). Issues that directly impact the Tg, such as instrumental parameters, sample preparation methods, data analysis, and “wet” vs. “dry” measurements, are discussed.

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