The crystallization
behavior and morphological features of particles
obtained from amorphous diprophylline (DPL) are reported. After fast
cooling of the melt, progressive heating above the glass transition
(T
g ≈ 37 °C) induces the nucleation
and growth of well-shaped crystals: PC for primary crystals. The combination
of differential scanning calorimetry, hot stage optical microscopy,
powder X-ray diffraction, and Raman spectroscopy revealed that these
PC are kinetically favored and can form spontaneously in the supercooled
melt whatever the enantiomeric composition, although their development
and relative stability are influenced by the presence of theophylline,
the main impurity in DPL samples. Specific crystal surfaces of the
PC act as favorable areas and support for the subsequent formation
of previously known metastable crystal forms consisting of solid solutions
of the two DPL enantiomers. This study demonstrates the complex multistep
mechanism that can occur during the temperature-induced crystallization
of chiral amorphous drugs, and their strong sensitivity to enantiomeric
composition and chemical purity.
Abstract:In this work, the apparent shear strength at the interface between a bamboo fiber and the surrounding poly(lactic acid) (PLA) matrix is quantified. A method for processing pull-out test samples within a controlled embedded length is proposed and the details of the test procedure are presented, along with a critical discussion of the results. Two series of samples are considered: untreated and mercerized bamboo fibers from the same batch, embedded in the same polyester matrix. Electron and optical microscopy are used to observe the fiber-matrix interface before and after the test, and to identify the failure mode of each sample, especially as regards the occurrence of fibrillation in the fiber bundles. The values of apparent interfacial shear strength are calculated only for regular fibers successfully pulled out from the matrix, and reported with their statistical variations. Mercerization, whose efficiency was proven by Fourier transform infrared (FTIR) spectroscopy, did not appear though to improve the quality of the interface (τ app = 7.0 ± 3.1 MPa for untreated fibers and τ app = 5.3 ± 2.4 MPa for treated fibers).
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