The cyclic amide ε-caprolactam (ε-CLA) is efficiently polymerized by thermally latent C-2-protected N-heterocyclic carbenes (NHCs) to give the corresponding polyamide (PA 6). Carbon dioxideand metal salt-protected NHCs were used as precatalysts, out of which the free carbenes were generated thermally. This way, a premixing of the corresponding initiator with ε-CLA was possible to yield a storable and directly polymerizable mixture. The screening of a variety of differently constituted carbenes showed the importance of basicity of the active species, thereby revealing N-alkyl-bearing tetrahydropyrimidinium-based carbenes as the most active ones. Rapid production of PA 6 in high yields was possible in bulk polymerization at 180 °C, the best activity displayed by 1,3-dicyclohexyltetrahydropyrimidinium-2-carboxylate (6-Cy-CO 2 ). In situ rheology during polymerization showed the characteristics typical for the anionic polymerization of ε-CLA.

Laurolactam (LL) is polymerized in the bulk using strongly basic N-heterocyclic carbenes (NHCs) as initiators at temperatures of 180−200 °C to prepare the corresponding polyamide (PA 12). In-situ rheology of the polymerization progress reveals that an anionic mechanism is active, which is supported by the strong dependence of initiator activity on the basicity of the NHCs. GPC data and kinetic investigations show the process to be moderately controlled and fast, allowing high or quantitative yields in short polymerization times. Fifteen different NHC−CO 2 −adducts and NHC−metal complexes were used as thermally labile but room temperature stable NHC-precursors. Depending on the ring size and N-substituent, some of these protected NHCs allow forming a mixture of monomer and NHC-precursor that is suitable for long-term storage and readily polymerizable by simple heating. All polymerizations are executed without activator or other additives and thus represent a true one-component system for the production of PA 12. Finally, LL is copolymerized with εcaprolactam (ε-CLA). It is found that a copolymer with a considerable gradient is formed, with ε-CLA being incorporated preferentially at the onset of the polymerization.

Incorporation of agricultural wastes as fillers in fiber-reinforced plastics is gaining momentum in plastics engineering research. In this study, fiber-reinforced polypropylene (PP) with rice and coffee husks as filler material were developed. The effect of alkali (sodium hydroxide) pretreatment of the husks on mechanical and thermal properties of developed PP biocomposites was observed. Filler material loading was varied from 0% to 20% for rice husks and 0% to 10% for coffee husks. A twin-screw extruder was used for compounding the PP matrix with rice and coffee husk filler materials. Tensile strengths and percentage elongation results varied from 27.4 to 37.4 MPa and 2.4% to 70.3% (unmodified coffee husks), 31.1 to 37.4 MPa and 5% to 70.3% (unmodified rice husks), 30.7 to 37.4 MPa and 5.3% to 70.3% (modified coffee husks), and 30.7 to 37.4 MPa and 4.8% to 70.3% (modified rice husks). Young’s modulus ranged between 1656 and 2247.8 MPa for biocomposite PP samples with unmodified filler material. Young’s modulus ranged between 1740 and 2160 MPa after alkali treatment of the filler material. Charpy impact strengths ranged from 1.2 to 4 kJ/m2 and 3.1 to 19.6 kJ/m2 for samples containing unmodified and modified filler material, respectively. Thermogravimetric analysis showed that an increase in filler content resulted into delayed weight loss at high degradation temperatures. The results suggest that these developed fiber-reinforced plastics can be used in applications requiring high thermal stability and good mechanical properties.

Development of high-speed reactive processing system for carbon fiber-reinforced polyamide-6 composite: Insitu anionic ring-opening polymerization AIP Conference Proceedings 1736, 020022 (2016) AbstractThe constructive design in the automotive industry, but also in many other industrial sectors has changed steadily over the past decades. It became much more complex due to e.g. increased use of hybrid materials. Combined with the desire to minimize the weight of vehicles and thus the CO 2 emissions, the use of low density materials and especially fiber-reinforced plastics is increasing. E.g. Continuous fiber thermoplastic composites are used to reinforce injection molded parts. Low viscosity monomers like caprolactam, which is used to produce polyamide 6 by anionic polymerization are able to easily impregnate and penetrate the textile reinforcement. After wetting the fibers, the ring-opening polymerization starts and the matrix is becoming a polymer. At IKT, a method based on the RIM process (reaction injection molding) was developed to produce continuous fiber thermoplastic composites with high contents of continuous glass fibers. The anionic polymerization of polyamide 6 was now combined with the pultrusion process. Continuous glass fibers are pulled through a mold and wetted with caprolactam (including activator and catalyst). After the material polymerized in the mould, the finished continuous fiber thermoplastic composites can be pulled out and is finally sawn off.

Analysis of aS ingle Screw Extruder with aG rooved Plasticating Barrel -Part I: The Melting ModelSingle screw extruders with barrier screws, grooved feed zones and grooved melting zones were introduced to the European plastics industry in 1999. These extruders have an improved melting and conveying capacity among other advantages, such as al ower melt temperature, less wear, less torque and less energy consumption. The aim of this paper is to present am athematical model for predicting the melting rate in this type of extrusion system. Based on the classical melting mechanism observed in conventional extruders, it was possible to study the effect of the geometry of the grooved barrel on the melting rate of apolymer. It was shown that the grooves on the barrel notably increase the melting rate, when compared to conventional single screw extruders. Ag ood agreement between theory and experimental data was found. 1I ntroductionThe single screw extruder (SSE) is one of the most important pieces of equipment in the polymer processing industry. Therefore, it is not surprising that there is alot of interest in improving this technology. Ahigh performance SSE usually has three distinctive characteristics. First, it has agrooved feed zone that improves solids conveying and throughput stability. Second, it has ab arrier screw that separates the melt from the solid, and finally, it has distributive and dispersive mixing elements at the end of the screw, which improve the quality of the melt.At the Institut für Kunststofftechnik (IKT) of the University of Stuttgart, anew type of high performance SSE has been developed. In addition to all the above mentioned characteristics, the grooves in the feed section extend along the melting section, as shown in Fig. 1. This technology was introduced to the European plastics industry in 1999 (Grünschloß, 1999), and it is currently commercialized under the brand name Helibar .It will be called Helibar -Extruder (HBE) in the following. Figure 1s hows the basic design of aH BE. Compared with the traditional grooved feed sections, the strict thermal separa-tion of feed and melting sections (heat barrier) is not necessary. The inner wall of the feeding section has tapered helical grooves and the barrel in the melting section is designed with flat axial or helical grooves. Because of the improved transport efficiency of the melting zone, the grooved feed zone can be largely released from its pressure build up task. Thus, the frictional heat produced in the feed zone is not too high, and it can be taken away with simple air cooling systems (radiators, fans). Grünschloß (2002;2003) and Chung (2011) conducted numerous experiments in order to study the effect of the grooved barrel on processing performance, particularly on mass throughput, pressure development, screw torque, and energy consumption. It was possible to show that the plastification efficiency was significantly improved in comparison to other high performance SSE. In several cases, an increase in the lifetime of the equipment was dem...