Plastisol Foaming Process. Decomposition of the Foaming Agent, Polymer Behavior in the Corresponding Temperature Range and Resulting Foam Properties

The decomposition of azodicarbonamide, used as foaming agent in PVC - plasticizer (1/1) plastisols was studied by DSC. Nineteen different plasticizers, all belonging to the ester family, two being polymeric (polyadipates), were compared. The temperature of maximum decomposition rate (in anisothermal regime at 5 K min-1 scanning rate), ranges between 434 and 452 K. The heat of decomposition ranges between 8.7 and 12.5 J g -1. Some trends of variation of these parameters appear significant and are discussed in terms of solvent (matrix) and viscosity effects on the decomposition reactions. The shear modulus at 1 Hz frequency was determined at the temperature of maximum rate of foaming agent decomposition, and differs significantly from a sample to another. The foam density was determined at ambient temperature and the volume fraction of bubbles was used as criterion to judge the efficiency of the foaming process. The results reveal the existence of an optimal shear modulus of the order of 2 kPa that corresponds roughly to plasticizer molar masses of the order of 450 ± 50 g mol-1. Heavier plasticizers, especially polymeric ones are too difficult to deform. Lighter plasticizers such as diethyl phthalate (DEP) deform too easily and presumably facilitate bubble collapse

Mean-field transport theory for the two-flavour NJL model

By making decomposition of the Wigner function simultaneously in both the spinor and the isospin spaces we derive a set of kinetic equations for the quark distribution functions and the spin densities. A detailed analysis of the consequences imposed by the chiral invariance on the form of the transport equations is presented.Comment: Revtex, 25 pages, no figure

Laparoscopic Roux-en-Y Gastric Bypass After Failed Vertical Banded Gastroplasty: a Multicenter Experience with 203 Patients.

BACKGROUND: Vertical banded gastroplasty (VBG) has long been the main restrictive procedure for morbid obesity but has many long-term complications for which conversion to Roux-en-Y gastric bypass (RYGBP) is often considered the best option. METHODS: This series regroups patients operated on by three different surgeons in four different centers. All data were collected prospectively, then pooled and analyzed retrospectively. RESULTS: Out of 2,522 RYGBP performed between 1998 and 2010, 538 were reoperations, including 203 laparoscopic RYGBP after VBG. There were 175 women and 28 men. The mean BMI before VBG was 43.2 ± 6.3, and the mean BMI before reoperation was 37.4 ± 8.3. Most patients had more than one indication for reoperation and/or had regained significant weight. There was no conversion to open surgery. A total of 24 patients (11.8 %) developed complications, including nine (4.5 %) who required reoperation and one death. With a follow-up of 88.9 % after 8 years, the mean BMI after 1, 3, 5, 7, and 9 years was 29.1, 28.8, 28.7, 29.9, and 28.8, respectively. CONCLUSIONS: On the basis of this experience, the largest with laparoscopic reoperative RYGBP after failed VBG, we conclude that this procedure can safely be performed in experienced hands, with weight loss results similar to those observed after primary RYGBP. In patients with too difficult an anatomy below the cardia, dividing the esophagus just above the esophago-gastric junction and performing an esophagojejunostomy may be a safe alternative to converting to a Scopinaro-type BPD, obviating the additional long-term risks associated with malabsorption