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Today PLA is one of the most important bioplastics on the market. A disadvantage of commercial polylactide is that it is not readily foamable, due to its low molecular weight, its low melt stability, and the lack of strain hardening effects. Therefore, commercially available polylactide has to be modified. In this study, the effects on properties by adding different modifiers were investigated. Adding of the modifiers and their chemical reaction were performed by means of reactive extrusion on a twin screw extruder. The molecular weight was increased by modifiers, which can be attributed to a changed chain topology. The highest molecular weight was achieved with organic peroxide. The rheological studies show that a changed chain topology can be assumed for the modified PLA. The most pronounced effect on the melt properties—the melt viscosity and also the melt strength—again was observed with the organic peroxide. The melt strength was increased for PLA modified with the organic peroxide. Furthermore, the organic peroxide was the only modifier that enhanced the crystallization rate, which is also favorable for extrusion foaming. POLYM. ENG. SCI., 57:1242–1251, 2017. © 2017 Society of Plastics Engineers

Underwater pelletizing of thermoplastic materials has gained high importance within the chemical and the compounding industry. It is known for producing comparatively spherical pellets with good bulk characteristics. Pellet shapes are determined by the viscous and elastic properties of the melt as well as various process conditions. Therefore, deformation of the melt strands because of the water flow at the die-hole opening may result in undesired shapes. This is particularly the case when processing polymers of low viscosity. This paper defines an analytical framework describing the pellet formation at the die-hole opening. Furthermore, a nondimensional DS number is developed as a measure for the deformation sensitivity of different polymer materials. In order to validate this approach, a new camera system and video recording method has been developed, which allows for a visual analysis of the cutting process in underwater pelletizing systems. Examining different materials at various process parameters, this paper identifies the main parameters responsible for pellet deformation and demonstrates how the DS number can be used to anticipate these effects. POLYM. ENG. SCI., 55:1170–1176, 2015. © 2014 Society of Plastics Engineers

While developing new polymers, a high level of stiff and simultaneously tough material behavior is an important goal. This study shows a new approach to optimize the stiffness/toughness behavior of polyamide 6 (PA 6) by incorporating both stiff and elastomeric nanofillers during melt compounding. For stiffness enhancement of PA 6, an organic-modified layered silicate (organoclay) was used, whereas to compensate for the toughness properties, a nanostructured PA 6/polyether block copolymer (PA 6-copo) was applied. In the first step, binary nanocomposites have been investigated whereby correlations between morphological and mechanical properties have been derived. Subsequently, these results have been used to adapt the processing conditions for the ternary nanocomposites. Despite a considerable interaction of both nanofillers the stiffness/toughness balance of the PA 6 nanocomposite has been optimized significantly. At a filler content of only 8 mass% organoclay and 8.3 mass% PA 6-copo, Young's modulus and tensile strength of PA 6 could be increased by 55% and 18%, respectively. In addition, the notched impact strength of PA 6 was enhanced substantially by 58%. POLYM. ENG. SCI., 54:247–254, 2014. © 2013 Society of Plastics Engineers

Since it is known that crosslinked polyethylene can be welded, it is clear that the mechanisms acting in the interior of a welded joint are not adequately explained yet. There are several criteria, hypotheses and models that attempt to describe what happens in a welded joint. In this paper, two new promising hypotheses, the Mixed Crystal Hypothesis and the Nexus Hypothesis, are introduced. The Mixed Crystal Hypothesis can be proven by the help of several different examination methods. Other examinations support the Nexus Hypothesis.