Rheology
Abolfazl Deylami; Abbas Kebritchi
Abstract
The time available for proper casting of the polyurethane (PU) system after isocyanate addition (called pot life) affects the macrodiol microstructure. In this research, the effect of molecular weight ( Mn ) of hydroxyl terminated polybutadiene (HTPB) as an important macrodiol on the pot life of polyurethane ...
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The time available for proper casting of the polyurethane (PU) system after isocyanate addition (called pot life) affects the macrodiol microstructure. In this research, the effect of molecular weight ( Mn ) of hydroxyl terminated polybutadiene (HTPB) as an important macrodiol on the pot life of polyurethane system was rheologically investigated. The chemorheological behavior of polyurethane systems based on five different HTPBs with Mn ranging from 2810 to 4450 g/mol and two common diisocyantes (TDI and IPDI) were studied in situ. The results showed that by increasing Mn , the rotational viscosity as well as the constant reaction rate of urethane formation increases; whereas the pot life of the polyurethane system decreases. The pseudoplastic behavior of the samples showed the minimum rate constant/longest pot life at a critical molecular weight (Mc) of about 3100 g/mol, which may be due to physical chain entanglements. Rheomechanical spectrometry interestingly depicted that tan δ originated-gel point occurs before the intersection of stored modulus (G') and loss modulus (G") (tgel< tG'=G"). The kinetic model developed by Hsich showed excellent agreement with the cross-linking data of three polyurethane systems.
Rheology
Maryam Shokrollahi; Bahereh T. Marouf; Reza Bagheri
Abstract
Dimethylbenzylidene sorbitol (DMDBS) is a common nucleating/clarifier agent used in polypropylene (PP). So many researchers have looked at different aspects of incorporating this additive on crystallization behavior of PP. The current study has focused on a rather new subject and that is the role of ...
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Dimethylbenzylidene sorbitol (DMDBS) is a common nucleating/clarifier agent used in polypropylene (PP). So many researchers have looked at different aspects of incorporating this additive on crystallization behavior of PP. The current study has focused on a rather new subject and that is the role of carrier resin of DMDBS masterbatch on the rheological behaviour of polypropylene. This goal has been achieved through studying the role of carrier resin on phase separation behavior of DMDBS upon cooling. It has been shown that a permanent bonding forms between the molecules of carrier resin and DMDBS in the masterbatch and this bonding slows down the crystallization kinetics of DMDBS in the final blend which in turn, influences its rheological behavior. Frequency sweep experiments conducted on a block co-polypropylene showed that lower values of storage shear modulus (G’), loss shear modulus (G’’), and complex shear viscosity (ɳ*) are observed if DMDBS is incorporated in the form of masterbatch. Interestingly, a different effect was observed when the masterbatch constituents were employed directly into the polypropylene, illustrating the importance of the mentioned bonding between DMDBS and the carrier resin in the masterbatch.
