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.

Five kinds of polylactides (PLAs), with different d-lactide contents and tacticities, were subjected to high-speed melt-spinning experiments. In addition to stereochemical purity, the PLA types differed in molecular mass and molecular mass distribution. The properties of the different PLA materials were characterized by thermogravimetry, differential scanning calorimetry, dynamic mechanical analysis, size exclusion chromatography, and 1 H-NMR and 13 C-NMR spectroscopy. The material was spun with a highspeed spinning process within the range 2000 -5000 m/min. The physical and tensile properties of the fibers were determined. The maximum tensile properties of the fibers were a 300 MPa tenacity at an elongation at break of 30% and a tensile modulus of 6.8 GPa.

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With the discussion of sustainability and the increased environmental awareness, the biopolymer poly‐β‐hydroxybutyrate (PHB) has gained more and more attention in recent years. It derives from renewable sources and can degrade in different environments to carbon dioxide and water. A hindrance for its potential application in plastics parts is its brittleness, deficiency in thermal stability and low crystallization rate. To overcome these problems chemical modification of PHB by reactive extrusion was carried out in a solvent‐free one‐step process by means of a twin screw extruder. Thermal and rheological characterization confirmed the branching and partial crosslinking of PHB by the organic peroxide tert.‐butylperoxybenzoate as well as by the reaction assisted multi‐functional coagents triallyl cyanurate and divinylbenzene. The crystallization temperature of the modified PHB could be significantly increased, up to 16 K, accompanied with an enhanced crystallization rate. Rheological studies show a distinct increase in the melt viscosity and the elastic properties dependent on the modifier content. The addition of plasticizers like rapeseed oil or polyethylene glycols (PEG 1500 and PEG 4000), respectively, lead to an increase in melt extensibility and melt viscosity. In case of PHB modified with PEG 1500, degradation reactions could be substantially retarded. POLYM. ENG. SCI., 59:1057–1064, 2019. © 2019 Society of Plastics Engineers