Influence of deformation on physical aging of polycarbonate

Summary Volume recovery of polycarbonate samples has been investigated by dilatometric and density measurements near ambient temperature. The volume changes with time have been measured either after heating above T_g and quenching, or after cold drawing at ambient temperature. Cold drawing drastically increases the volume recovery rate of polycarbonate, as compared with the rate observed after quenching. This is quite similar to the behavior previously reported on physical aging measured by dynamic mechanical tests (1). The observed decrease of specific volume after cold drawing can be explained by a densification effect due to molecular orientation.     

Dynamic mechanical behaviour of random copolymers of a LC-methacrylate and octyl methacrylate

The dynamic mechanical behaviour of random copolymers of LC monomer-1-(hexyloxycarbonyl)ethyl 4-[4-(methacryloyloxy)benzoyloxy]benzoate (HB) and octyl methacrylate (OMA) was studied in the main transition and flow regions. Even though the aliphatic end groups of the side chain of HB and OMA are roughly the same, the T _g temperature of poly(HB) is ∼ 80 K higher than that of poly(OMA); this fact is due to the presence of the stiff phenyl benzoate mesogenic group in the side chain of HB. With increasing content of OMA in the copolymer the superimposed curves of the storage G′ _p and loss G′′ _p moduli at a constant temperature shift towards shorter frequencies. It has been shown that this shift is mainly due to an increase of the free volume in the copolymers with increasing content of OMA. While HB monomer shows liquid crystalline (LC) properties, its polymer (poly(HB)) and random copolymers with OMA show only isotropic thermal behaviour because no flexible spacer is present in the side chain of HB which would decouple the main chain and mesogenic group motions. This means that neither the homopolymer of HB, nor its copolymers with a flexible comonomer retain the LC properties of the starting LC monomer, HB. Received: 26 September 1996/Revised: 7 November 1996/Accepted: 7 November 1996     

Design and characteristics of gellan gum beads for modified release of meloxicam

The aim of the presented work was to design, formulate and evaluate the properties of low-acyl gellan macro beads with the potential application as carriers for oral delivery of meloxicam (MLX) in the prophylaxis of colorectal cancer. The beads were obtained by means of ionotropic gelation technique. Calcium chloride (1.0%, 9.0?×?10^?2 M) was used as the cross-linking agent. Nine different polymer, drug and surfactant (Tween^®80) mixtures were used for production of the beads. The quantitative compositions of the mixtures were generated with the application of the Design of Experiments (DoE) modulus from the STATISTICA Software. The prepared formulations revealed 7.2–27.0% of drug loading and 29.2–50.7% drug encapsulation efficiency. It turned out that 0.5% amount of gellan gum in the mixtures was not sufficient to obtain spherical beads. The morphology and surface of the dried beads were analyzed by SEM. Raman spectra confirmed that MLX did not undergo structural changes during production of the beads. The swelling behavior and degradation of the beads were evaluated in three simulated gastrointestinal fluids at different pH (1.2; 4.5; 6.8). The MLX in vitro release studies were conducted on USP apparatus IV, working in the open loop mode. The obtained results showed that MLX release from the dried beads was pH-dependent. The formulations obtained from mixtures containing 1.0 and 1.5% of gellan may be considered as oral dosage forms for MLX, intended to omit the stomach and release the drug in the distal parts of the gastrointestinal tract.     

Granzyme B mimics apical caspases. Description of a unified pathway for trans-activation of executioner caspase-3 and -7

Granzyme B (GrB) is predicted to trigger apoptosis by activating preferred caspases, but the zymogens that are directly processed by the granzyme and the requirements for these interactions remain unclarified. We examined this dilemma by comparing the kinetics and pattern of GrB-mediated activation of the executioner caspase-7 in vitro and in vivo. GrB rapidly activates procaspase-7 in vitro by cleaving between the large and small subunits leaving the propeptide intact. During GrB-mediated apoptosis, the caspase-7 propeptide is removed and cleavage occurs between the subunits. Strikingly, caspase-7 is unprocessed in caspase-3-deficient MCF-7 cells exposed to GrB but is rapidly activated when the cells are solubilized. Transfection with caspase-3 restores the removal of the caspase-7 propeptide and the capacity of GrB to subsequently activate the caspase. The data suggest that GrB activates caspase-3, which then removes the propeptide of caspase-7 allowing activation by GrB. Thus GrB initiates the death pathway by processing the accessible caspase-3, and the caspase-7 propeptide regulates trans-activation of the zymogen by granzyme. As a consequence, two proteases, caspase-3 and GrB, are required to activate procaspase-7.     

Radionuclide imaging and ultrasound in liver/spleen trauma: a prospective comparison

In a prospective blind study of liver/spleen trauma, 32 consecutive patients were evaluated by radionuclide imaging (99mTc-sulfur colloid) and gray-scale ultrasound. Six patients (19%) had inadequate sonograms due to injuries and pain. Thirteen (41%) were normal, 13 (41%) were abnormal with one technique or the other, and there was a discrepancy in 2 (6%). Of the 13 abnormal patients, 1 had a lacerated spleen, 2 had angiographic confirmation of a subcapsular hematoma, and 10 showed resolution on follow-up. Two patients with left-sided trauma had abnormal radionuclide scans of the liver; sonograms were initially normal in one of them, but subsequent imaging confirmed the abnormality. The authors feel that imaging with 99mTc-sulfur colloid should be the primary screening examination for liver/spleen trauma.     

Fundamental high-frequency performance limit for impatt mode operation

It is well known that the phase delay associated with carrier energy relaxation in impatt diodes tends to improve their performance. The purpose of the letter is to point out that there is also an amplitude degradation effect which tends to impair impatt performance. At high enough frequencies the amplitude degradation effect dominates, leading to a high-frequency performance roll-off. The net effect of energy relaxation is believed to be deleterious for frequencies above about 500 GHz for Si devices, and at lower frequencies for GaAs devices.     

Experimental study of the miscibility of ABS/PC polymer blends and investigation of the processing effect

In the challenging prospect of developing new materials by mixing different polymers to reach a synergetic performance, the present research focuses on the study of the miscibility of two polymers: The acrylonitrile butadiene styrene (ABS) composed of a dispersed elastomeric (polybutadiene rubber) polymer embedded in a SAN thermoplastic matrix, and the polycarbonate (PC). It shall be noted that obtaining miscible polymer blends is often a difficult task because of the large size of their molecular chains and the high interfacial tension between the polymer phases. Until now, the most numerous researches developed in this field involve polymer blends obtained by compatibilization techniques in order to improve the interfacial adhesion between initial polymers. The aim of this work is to study the miscibility between ABS and PC. First, two different methods were used to mix the polymers: the twin‐screw extrusion and the dissolution in a common solvent tetrahydrofuran (THF). Then, physicochemical, microscopic observation and rheological characterization were performed on samples of mixtures obtained by both extrusion processing and dissolution method. The measurement of glassy transition temperature (T_g) by differential scanning calorimetry measurements (DSC) and dynamical mechanical thermal analysis (DMTA) have shown a partial miscibility between the two polymers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44975.