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In order to reduce the potential fire load, polyamides are often compounded with flame-retardant additives like red phosphor or halogenous, nitrogenous or phosphoric molecules. However, to achieve an effective flame retardancy, very high amounts of the additives are necessary, which can negatively affect the mechanical properties of the material or lead to a migration of the additive to the surface of the compound (if the flame retardant is physically bonded to the polyamide). A new attempt to enhance the flame resistance of polyamides is the direct integration of the respective molecules within the polymer chain during the polymer synthesis. By applying this method, the flame-retardant additives function as a chain regulator, which results in low molecular weights and low viscosities. Consequently, these polyamides are difficult to process. Therefore, in this work intrinsically flame-retardant polyamides were compounded with a PC/PA-Blend as a linear chain extender in a twin-screw extruder. The compounds were characterized regarding their rheological and flame-retardant properties. Rheological measurements showed that the viscosity of standard-polyamide was reached and that the chain extension was successful. Thereby, processing through injection molding was possible. Furthermore, a flame test was conducted by measuring the burning duration after two flame treatments. The experiments showed that the polyamide keeps its flame retardancy after the compounding process, which makes the treated polyamide suitable for conventional industry applications. [ABSTRACT FROM AUTHOR]

Cast polyamides, which are synthesized through anionical polymerization in a forming mold, have a high molecular weight compared to polyamides synthesized through polycondensation. However, high amounts of wastes (e.g. unusable sprues, post-processing wastes) occur with this production method. Because of this and due to the high molecular weight of the cast polyamide, compounding of the wastes and a further processing via methods like thermoforming is a potential approach for the recycling of polyamide wastes. However, when the polyamide wastes are recycled in a twinscrew extruder, the remaining catalyst, which is embedded within the wastes, can lead to a degradation of the polyamide chains. This degradation results in molecular weights respectively melt viscosities, which are suitable for processing via injection molding but not suitable for methods like thermoforming, for which high viscosities are necessary. In this work, cast polyamide wastes were compounded in a twin-screw extruder with additives to obtain maximum viscosities. We considered (mono- and di-)carboxylic acids, which act as catalyst catchers, as well as different additives, which increase the molecular weight, (linear chain extenders and multifunctional polymeric backbones). After the compounding, rheological measurements were conducted to examine the degree of the viscosity increase and thermal measurements to estimate a processing window for thermoforming. The rheological measurements showed that the increase is strongly dependent on the waste batches, which were used for the respective test series. However, the thermal properties were not influenced through the polymer modification. Overall, viscosities could be reached, which were high enough to produce semi-finished parts out of the compounds. Additionally, thermoformed polyamide parts with exact forming shape as well as constant wall thicknesses were realized. [ABSTRACT FROM AUTHOR]

Cast polyamide 6 is anionically polymerized from ε-caprolactam. Its good properties are mainly caused by the higher molecular weights, compared to standard polyamide 6. Because of sprues and post-processing, a larger amount of scrap is produced. This scrap is typically incinerated without sufficient use of its high quality properties. However, cast polyamide 6 also offers great potential for material recycling, particularly if its high molecular weight can be retained. As cast polyamide decomposes during processing as well, it is necessary to add some agents during compounding. By adding a carboxylic acid during compounding, it is possible to adjust the molecular weight and thus the flowing behavior of the polyamide recyclate melt. The highly viscous recyclates are usable for blow molding applications. [ABSTRACT FROM AUTHOR]

The importance of the bioplastic polylactide has increased significantly in the recent years. Due to its quite similar properties to fossil-based polystyrene (PS), it has the potential to substitute foamed PS products and consequently can increase the sustainability and material efficiency of foamed products. However, the low molecular weight of commercial PLA, its sensitivity to hydrolysis during processing and its low rate of crystallization inhibit the production of low density foams and uniform cell morphology. The addition of different modifiers to optimize the melt strength and melt viscosity was performed by means of reactive extrusion. The rheological and thermal properties as well as the foam densities were examined. The melt viscosity and melt strength was increased. Foams with fine and closed-cell structure with relatively thin cell walls were made in batch foaming experiments. [ABSTRACT FROM AUTHOR]

Polylactide (PLA) is one of the most important bioplastics on the market with a permanent growth in production capacity. Due to its good mechanical properties, it is comparable to polystyrene. But in terms of foaming the melt strength and extensibility of commercial polylactide are rather low. Therefore such commercial grades often need to be chemically modified to induce crosslinking, chain extension or grafting by means of reactive extrusion on a twin-screw extruder. In this work different polylactide grades were used, to better understand the influence of the molecular characteristics, such as molecular weight, acid value and D-content, not only on the modification mechanism, but also on the foam properties. [ABSTRACT FROM AUTHOR]

Bioplastics, which will see rising demand in the next years, have to be compounded by using a twin screw extruder like conventional plastics. By using a twin-screw extruder, the molecular weight of the bioplastic polyhydroxybutyrate (PHB) can be degraded under control. In a second step, the short-chain PHB and a soft phase can be compounded to a larger block copolymer by means of reactive extrusion. The processing step takes place in a process- and material-efficient manner without catalysts, solvents and purification processes. The development of the block copolymer improves the ductile properties of the material without changing the thermal or chemical characteristics. [ABSTRACT FROM AUTHOR]

Polyamide 6 can be produced by anionic ring-opening polymerization of ε-caprolactam using e. g. sodium-caprolactamate as a catalyst. One of the best known anionically polymerized polyamide 6 is so called cast polyamide 6, used for particularly stressed parts. The reason for its good mechanical properties is the comparably high molecular weight. When using cast polyamide 6 for extrusion or injection molding, its high molecular weight can be a disadvantage due to its very high viscosity. To enhance processability, the flow behavior of these materials has to be adjusted. Besides the use of a lubricant, shorter chains would be another way to achieve better processability. In this work, the latter is performed by compounding anionically polymerized cast polyamide 6 using a chain scissorer, e. g. terephthalic acid. Compounding of dry-blends made of cast polyamide 6 and said terephthalic acid is done on a twin-screw extruder type ZSK 26MC of Coperion, Stuttgart. Mechanical properties and flow behavior were investigated afterwards. Surprisingly, it could be shown, that adding very small amounts of terephthalic acid did not reduce but raise viscosity significantly. However, higher amounts of terephthalic acid reduce these viscosities, as expected. Additionally, a reduction of viscosity can be seen over time, because remaining ingredients seem to still be active. Mechanical properties such as Young’s modulus or tensile strength are not affected by adding terephthalic acid and are comparable to those of injection molding polyamide 6. Solely impact strength was slightly reduced, when a larger amount of terephthalic acid was added. [ABSTRACT FROM AUTHOR]

Cast polyamide 6 is a high-quality material due to its long polymer chains. Because of sprues and post-processing, a comparably large amount of the produced material, up to 30 %, becomes waste. Until today, this high-quality waste is burned or added into standard virgin polyamide 6 raising its molecular weight. Instead of using cast polyamide waste as an additive or combustion material, it would be beneficial to process high-molecular weight recyclates made of this cast polyamide 6. To enhance its processability, using a lubricant as a processing additive is a reasonable approach. Our previous findings within this field revealed an unusual behavior of a lubricant consisting of a polyester modified wax, which is already used for standard polyamide 6 without known problems. In this work, milled cast polyamide 6 chips obtained from machining are washed and dried and then used for producing high-molecular weight recyclates. In literature the deposition of such waste is recommended because of pollution and contaminations. It is hence possible to get clean material for recycling. The recycling step itself is performed on a twin-screw extruder type ZSK 26MC of Coperion, Stuttgart, by processing a dry-blend of cast polyamide and said lubricant. Rheological measurements show increasing complex viscosities of recyclates depending on the lubricant’s content. It is possible to achieve viscosities higher than those of the solely processed polyamide recyclate. Even the viscosity of unprocessed cast polyamide 6 can be reached. Compared to virgin extrusion polyamide 6, the processed recyclates achieve higher tensile strengths, while an increasing amount of lubricant does neither affect Young’s modulus nor tensile strength. It is also shown that the lubricant raises impact strength significantly. [ABSTRACT FROM AUTHOR]