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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.sup.-1] scanning rate), ranges between 434 and 452 K. The heat of decomposition ranges between 8.7 and 12.5 J [g.sup.-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 -[+ or -]- 50 g [mo1.sup.-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. POLYM. ENG. SCI., 53:1712-1718, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION Polymer foams are products with an excellent balance of properties mainly, light weight, low density, outstanding strength/weight ratio, superior insulating abilities and energy absorbing performance. They are especially attractive [...]

Polyethylene connection pipes of wall thickness ranging from 3.0 to 4.5 mm, used for 0, 5, 9, 12, and 18 years in the French network of drinking water disinfected by bleach, have been analyzed. The stabilizer thickness profiles reveal that bleach destroys the stabilizer in a superficial layer of about 0.5 mm depth at the water-polymer interface. In the rest of the wall, stabilizer is lost by physical processes, i.e., transport by diffusion into the bulk, extraction at the water-polymer interface, and evaporation at the polymer-air interface. The whole loss kinetics is governed by extractionand evaporation. The classical scheme for evaporation-diffusion process has been used to model physical loss processes, but with boundary conditions different from the literature ones. Concerning chemical aspects, some mechanisms proposed in the literature are criticized. The identification of the bleach reactive species remains an open question. POLYM. ENG. SCI., 51:1541-1549, 2011. © 2011 Society of Plastics Engineers, INTRODUCTION A polyethylene (PE) pipe transporting water at temperature T and pressure p (inducing a hoop stress σ ) is expected to undergo failure after a finite time tF. Here, [...]

Aging of unfilled polyethylene (PE) films in concentrated (80-100 ppm) chlorine dioxide (DOC) solutions at 20°C and 40 has been studied by IR spectrophotometry, melt rheometry, chlorine titration, and tensile testing to establish the mechanisms of PE degradation induced by DOC, to determine some important kinetic parameters, to identify the embrittlement mechanism, and to examine the possibility to predict nonempirically embrittlement from a kinetic model. Experimental results reveal that DOC initiates PE oxidation. This latter is responsible for hydroperoxide build-up, and chain scissions occur when hydroperoxides reach a critical concentration above which they decompose bimolecu-larly. The weight average molar mass [M.sub.w] decreases and embrittlement occurs when [M.sub.w] approaches a value of 70 kg [mol.sup.-1] as previously found in thermooxidation studies. A mechanistic scheme involving all the elementary steps of PE autooxidation plus one initiation and one termination step involving DOC has been elaborated. The kinetic scheme derived from this mechanistic scheme has been solved numerically and the results of simulations have been compared with experimental results. POLYM. ENG. SCI., 49:1429-1437, 2009. © 2009 Society of Plastics Engineers, INTRODUCTION It is well known that the polyethylene (PE) pipes containing pressurized water undergo failure after a time [t.sub.F] which is a decreasing function of pressure p and temperature T. [...]