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Biocomposites containing natural fibers and biopolymers are an ideal choice for developing substantially biodegradable materials for different applications. Polylactic acid is a biopolymer produced from renewable resources and has drawn numerous interest in packaging, electrical, and automotive application in recent years. However, its potential application in both electrical and automotive industries is limited by its flame retardancy and thermal properties. One way to offset this challenge has been to incorporate natural or synthetic flame retardants in polylactic acid (PLA). The aim of this article is to review the trends in research and development of composites based on agricultural fibers and PLA biopolymers over the past decade. This article highlights recent advances in the fields of flame retardancy and thermal stability of agricultural fiber‐reinforced PLA. Typical fiber‐reinforced PLA processing techniques are mentioned. Over 75% of the studies reported that incorporation of agricultural fibers resulted in enhanced flame retardancy and thermal stability of fiber‐reinforced PLA. These properties are further enhanced with surface modifications on the agricultural fibers prior to use as reinforcement in fiber‐reinforced PLA. From this review it is clear that flame retardancy and thermal stability depends on the type and pretreatment method of the agricultural fibers used in developing fiber‐reinforced PLA. Further research and development is encouraged on the enhancement of the flame retardancy properties of agricultural fiber‐reinforced PLA, especially using agricultural fibers themselves as flame retardants as opposed to synthetic flame retardants that are typically used. [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

Examines the Mixed Crystal Hypothesis and the Nexus Hypothesis, hypotheses designed to explain the mechanisms acting in the interior of a welded joint of crosslinked polyethylene. Experiments to evaluate the Mixed Crystal Hypothesis; Examination of the Nexus Hypothesis.

Structure–property relations between the blend morphology and the fracture mechanical behavior of immiscible polyamide 6/ethylene‐octene copolymer (PA6/EOR) blends are investigated. The influence of a moisture uptake of the PA6 on the blend behavior is also demonstrated. Different blend formulations lead to different blend morphologies, which vary in particle sizes, interparticle spacing, and intensity of the phase connectivity between the blend partners. The intensity of the phase connectivity is described by the rheological behavior. The morphology, defined by the particle size and the calculated interparticle spacing, is analyzed optically by a scanning electron microscope. The shift of the glass transition temperature of the blends due to moisture uptake is demonstrated via dynamical mechanical analyses. All parameters are linked to the fracture mechanical properties determined by the method of the essential work of fracture. By means of the method of the essential work of fracture it is shown that the toughness increase by a given material combination and a constant soft phase amount depends only on the particle size. However, a basic requirement is always strong phase connectivity between the blend partners. Thus, by a given material combination the smaller the soft phase particles within the matrix, the higher the increase in toughness. A moisture uptake does influence the blend properties in many ways and also leads to a change in the fracture behavior. Therefore, it is not possible to predict the fracture mechanical behavior of hydrophilic blends from one condition state to another. [ABSTRACT FROM AUTHOR]