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Advancements in Foam Injection Molding
Published in S. T. Lee, Polymeric Foams, 2022
The RIC-FOAM process has been applied to the foaming of PP,34,35,37 PA6,35 PPS35 and PLA. In this book, some results of PP FIM with the RIC-FOAM process are introduced. A 35-ton clamping force electric injection molding machine (J35AD-AD30H, JSW, Hiroshima) with a 22 mm diameter screw was used to prepare the foamed samples. The mold consisted of a rectangular cavity, and the dimensions were 70 mm × 50 mm × 2 mm. The polymer was high-tacticity isotactic polypropylene (i-PP) (F133A, Prime Polymer Co., Ltd.). The melt flow rate was 3 g/10 min (230°C). The weight-averaged molecular weight, Mw, was 379,000, and its tacticity was 97%. The gelling agent 1,3:2,4 bis-O-(4-methylbenzyliden)-D-sorbitol (Gel-all MD, New Japan Chemical Co., Ltd.) was used as a bubble nucleating agent. To produce different expansion ratios of foams, core-back operation was conducted with different core-back distances, i.e., moving distances of a portion of mold. The details of the processing conditions for the experiments are listed in Table 8.1.
Blown Film Technology
Published in Nicholas P. Cheremisinoff, Elastomer Technology Handbook, 2020
Polypropylene is an important polymer for the blown film industry. It is produced by stereospecific catalysis under condition similar to HDPE. The difference is that a methyl group is pendant from every other carbon atom of the backbone. The similarity is that there are almost no side chains formed in the polymerization. The methyl groups stiffen the backbone of the polymer and give it a higher melting point and tensile strength than HDPE. The stereochemistry can produce atactic, isotactic, or syndiotactic polymer — tacticity referring to the position of alternating methyl groups relative to the backbone. The most common commercial polymer is isotactic where the methyl groups are all on one side of the backbone. This arrangement allows the polymer to readily crystallize. The high rate of crystallization makes the polymer impossible to blow by the normal processes and requires some type of bubble quenching quickly after inflation. More will be discussed later about this.
The Chemistry of Polyurethane Copolymers
Published in Nina M. K. Lamba, Kimberly A. Woodhouse, Stuart L. Cooper, Polyurethanes in Biomedical Applications, 2017
Nina M. K. Lamba, Kimberly A. Woodhouse, Stuart L. Cooper
Polymers are a class of high molecular weight materials, with a structure that is characterized by “building blocks” of repeat units or monomers. The monomers react together to form long chains of repeating chemical units. The polymer chains that result may be linear or form a branched or three-dimensional network. Polymers can be classified in a number of ways, for example, according to whether they are of natural origin, or synthetic. Naturally occurring polymers include polysaccharides, cellulose, silk and natural rubber. Common synthetic polymers include polyethylene, polystyrene, Polyvinylchloride, polyesters, polytetrafluoroethylene, polycarbonates, and the polyurethanes. Polymers also can be classified according to chemical composition, chemical structure, physical state, thermal behavior and application. Classification on the basis of chemical composition of the polymer considers the elemental composition and types of monomer residues within the chain. The chemical structure considers the stereoregularity of the polymer, and the placement of side chains, which also is referred to as the tacticity of a polymer. The physical structure of the material also can be used, to classify materials as crystalline or amorphous, indicating the state of order of the molecules, or to indicate whether or not the polymer chains are branched as opposed to linear. The thermal behavior of the polymer also can categorize polymers as either thermoplastic or thermosetting, which is an important consideration in processing. The ultimate application of the material also can be used to classify polymers.
Generation of well relaxed all atom models of stereoregular polymers: a validation of hybrid particle-field molecular dynamics for polypropylene melts of different tacticities
Published in Soft Materials, 2020
Antonio De Nicola, Gianmarco Munaò, Nino Grizzuti, Finizia Auriemma, Claudio De Rosa, Agur Sevink, Giuseppe Milano
Tuning the properties of the material, by selecting appropriate tacticity, allowed the stereoregular polypropylene (and more in general vinyl stereoregular polymers) to become one of the most relevant materials of the polymer industry.[4,5] For semicrystalline polymeric materials, of course, tacticity is one of the key features determining most of the properties involved in several applications. Even in the case of fully amorphous materials or polymer melts, the tacticity plays an important role in influencing the final material behavior. In particular, in this case, tacticity is effective in the behavior of several properties such as: glass transition temperature (Tg),[6–8] self-diffusion coefficient (D),[8] entanglement molar mass (Me),[9] and other rheological properties.[10,11] Since tacticity mainly influences the torsional angle distributions of the polymer backbone, the main molecular effects on single chain properties are connected to changes in chain stiffness. For this reason, both experimental and theoretical studies have been conducted to understand the effect of tacticity on the stiffness of polymers. The chain stiffness can be quantified by the Flory’s characteristic ratio () or by the Kuhn length (b). Higher values of correspond to stiffer chains. The stiffness of polypropylene (PP) as function of the tacticity was experimentally estimated by measuring the differences in Tg,[7] intrinsic viscosity in solvent,[12,13] and chain dimension by SANS measurements.[14,15] From the theoretical point of view, the Rotational Isomeric State model (RIS) applied to an unperturbed single chain was used to estimate the effect of tacticity on the PP chain dimension and conformational energy.[16–18] Antoniadis et al. reported a Molecular Dynamics (MD) study to address the effect of tacticity on the dynamics of PP chains in melt state.[19,20] More recently, Tzounis et al. studied the effect of tacticity on the conformational properties of PP homopolymer melts and poly(ethylene-propylene) block copolymers by using single-chain Monte Carlo (MC) technique.[21] More generally, MD and MC techniques applied to atomistic and coarse-grained (CG) models were proposed to investigate the effect of tacticity on several physicochemical polymer properties.[18–26]