[en] Polyethylene foams, produced by radio-induced crosslinking, show a smooth and homogeneous surface, when compared to chemical crosslinking method using peroxide as crosslinking agent. This process fosters excellent adhesive and printability properties. Besides that, closed cells, intrinsic to these foams, imparts optimum mechanical, shocks and insulation resistance, indicating these foams to some markets segments as: automotive and transport; buoyancy, flotation and marine; building and insulation; packaging; domestic sports and leisure goods. We were in search of an ideal foam, by adding 5 to 15% of blowing agent in LDPE. A series of preliminary trials defined 203 degree sign C as the right blowing agent decomposition temperature. At a 22.7 kGys/dose ratio, the lowest dose for providing an efficient foam was 30 kGy, for a formulation comprising 10% of azodicarbonamide in LDPE, within a 10 minutes foaming time

[en] OIT's oxidation condition is very harsh for pure and irradiated polymers, particularly PP. PP undergoes pronounced molecular weight degradation in the course of processing and is prone to very fast oxidation and consequently very fast degradation, especially on samples submitted to previous aging and irradiation. We developed a more useful method applicable by a much broader set of resins. Our group has recently introduced a new procedure to determine OIT, in non-stabilized and stabilized, irradiated and non-irradiated polypropylene. The new procedure was based on two main features: (1) starting the oxidation on melted samples at temperatures as low as possible; (2) oxidation under slow heating conditions. So each sample has a set of two values of time and temperature, as the new method is not isothermal any longer, so we better call it 'Temperature dependent oxidative induction-time'. The new method showed itself as reproducible, sensitive to small changes in additive compositions and simple and inexpensive

[en] Organic materials undergo degradation reactions in the presence of oxygen. Most of known polymers have structural elements that are prone to oxidative degradation reactions: inadequate antioxidant content can contribute to this failure. Associated to it, radiation can impart to thermoplastic polymers, at a given level, non desirable effects, compromising, this way, 'end-use' of final product. A new Temperature-Oxidative Induction Time TOIT (once conventional ASTM-D-3895-95 method showed itself useless for this purpose), is being developed, in order to evaluate radiation effects in PP, under controlled oxygen atmosphere. Basically, it deals exclusively with a special temperature program, involving dynamic and isothermal techniques, comprising too final TOIT determinations in molten state samples. In resume, the whole test is carried out under nitrogen environment; at approximately 150 deg C, oxygen is introduced, causing initial breakdown of antioxidant protection, accompanied by energy releasing and an upward deflection of the curve above baseline. The changeover point to oxygen flow is considered the zero time of analysis. Both Polypropylene (PP), stabilized and non-stabilized (irradiated and non-irradiated) ones were assessed; TOIT within a range from 11 to 35 minutes were achieved, as per well defined thermograms. (author)

[en] Polyvinyl-pyrrolidone has been used as base material for wound dressing. Irradiation of the hydrogel compound was performed for initiation of crosslinking reaction to produce a irreversible gel and also for the final product. For wound dressing purpose, it is important to know the mechanical behaviour and the absorption of exudate of these polymeric systems. Membranes were prepared with 4 % PVP, 3 % PEO and 0,8 % agar nd irradiated with 10 to 40 kGy. The elongation at break showed a market decrease as a function of dose, while the tensile strength showed a opposite behaviour. Swollen experiments were also conducted to evaluate the capacity of exudate absorption from the wound. A irradiation dose of 10 kGy showed about 4 times more absorption than 40 kGy irradiation dose. Thus, this polymer system can be fitted to cope with the various mechanical and absorption requirements of a wound dressing. (author). 3 refs., 1 fig., 2 tabs

[en] PP suffers from low melt strength, i.e., the melted PP does not exhibits an increase in resistance to stretching during elongation. It is well known that the melt-strength properties of a polymer increase with molecular weight and with long chain branching due to the increase in the entanglement level (high melt strength PP-HMSPP). In spite of been the most fast growing polymeric commodity nowadays those new grades of PP and its development have been barely studied and its general chemical characterization have been even less studied with few exceptions. HMSPP as proposed by Montell patents are produced by low temperature and low dose irradiation of high molecular weight isotatica PP in N₂ atmosphere. So the well-known reactions would be mostly degradation and crosslinking. Degradation however is supposed to be the first and more intense reaction a the initial steps as already shown. So, according to Montell patents, another reaction is likely to occur, branching or T links competing with crosslinkings or H links. Radical are likely to decay very fast in amorphous phase, but under annealing the radicals entrapped in the crystal phase is likely to move to the boundary and react. The group of professor Silverman has already hypothesized in T links formation and also studied the radical decay of PP. It is easy to understand the difficulties in differentiate Hs from Ts links and even these links if in very small amount from the bulk or from virgin polymer, as the Ts links and even these links if in very small amount from the bulk or from virgin polymer, as the chemical groups and links are chemically speaking essentially the same