On crystallisation and fracture toughness of poly(phenylene sulphide) under tape placement conditions

Fibre reinforced thermoplastic tapes are subjected to high heating and cooling rates during the tape placement process. Such high cooling rates can significantly inhibit the crystallisation of the thermoplastic polymer and thereby affect its mechanical properties, such as strength or toughness. In the present work, the crystallisation of poly(phenylene sulphide) (PPS) subjected to high cooling rates was investigated using a fast scanning calorimeter. The PPS was found to be unable to crystallise when subjected to cooling rates higher than 20°C s−1. The influence of the degree of crystallinity on fracture toughness was investigated using an essential work of fracture approach. The amount of plastic work during the fracture process was found to decrease after moderate annealin

Effect of the cooling rate on the nucleation kinetics of poly(l-Lactic acid) and its influence on morphology

Although the crystallization kinetics of PLLA is slow enough to allow one to obtain amorphous samples by cooling from the melt at moderate rates, surprisingly, at the same time, the formation of crystallization nuclei is difficult to avoid. Their amount depends on the cooling rate from the melt:  the higher the cooling rate, the lower the amount of available nuclei after reaching the glass state. Cooling at controlled rates of 5−300 °C/min was performed by making use of a relatively new high-speed calorimetry technology, high-performance DSC (HPer DSC). Subsequent isothermal cold crystallization of amorphous PLLA, at different temperatures distributed across the bell-shaped crystal growth curve, was shown to depend on the rate at which the glass state was attained, reflecting the number of nuclei formed. However, (only) after complete cold crystallization, the DSC heating curves and the resulting morphology measured by optical microscopy and AFM were shown to be independent of the previous cooling rate into the glass, i.e., of the number of nuclei formed during the cooling process. In cases where the DSC heating curves subsequent to isothermal cold crystallization show two melting peaks, their origin, recrystallization, was clarified by heating at rates varying from 10 to 300 °C/min. The morphologies of the cold crystallized systems have been assessed by AFM and were correlated with the calorimetric results. Using HPer DSC, isothermal cold and hot crystallization at the same temperature has been studied successful

Microfocus wide-angle X-ray scattering of polymers crystallized in a fast scanning chip calorimeter

Microfocus wide-angle X-ray scattering (WAXS) has been applied for analysis of the polymorphism of isotactic polypropylene and polyamide 6 prepared in a fast scanning chip calorimeter (FSC). Samples with a typical mass of few hundred nanograms, and lateral dimension and thickness of about 100 m and 20 m, respectively, were exposed to a defined thermal history in the FSC and subsequently analyzed regarding the X-ray structure at ambient temperature using an intense synchrotron microfocused X-ray beam. The relaxed melt of isotactic polypropylene was cooled at rates of 40 K s-1 and 200 K s-1 which allowed formation of -crystals or mesophase, respectively. Polyamide 6 was isothermally crystallized at 95 ¿C and 180 ¿C which led to formation of -mesophase and -crystals, respectively. This study demonstrated,for the first time, that FSC polymer crystallization experiments could be completed and expanded by subsequent in situ structure analysis by X-ray scattering

Fast scanning calorimetry clarifies the understanding of the complex melting and crystallization behavior of polyesteramide multi-block copolymers

cited By 3Fast scanning calorimetry has been applied in order to understand the phase transitions in thermoplastic elastomers (TPEs) based on well-defined multi-block copolymers made of ‘soft’ polytetrahydrofuran and ‘hard’ terephthalate ester diamides. The intrinsically complex chemical structure of TPEs leads to complex phase transitions. By changing their thermal history over a wide range of temperature (from −100 °C to 200 °C) and cooling rates (from 10 to 4000 °C s−1), we clarify the origins of the various phases present in these materials. In particular, we study the different possibilities for the hard segments to associate depending on their mobility during the quenching phase, forming either strong and stable structures or weaker and metastable ones. Besides, we demonstrate that a minimal cooling rate of 800 °C s−1 is necessary to keep these TPEs (made of short and monodisperse hard segments) amorphous leading to a subsequent cold crystallization when heating back, at around 30 °C. Finally, we validate our interpretations by varying the copolymer composition (from 10 wt% to 20 wt% hard segments), revealing the thermal invariance of poorly organized domains. Based on these data, we also discuss the importance of chain diffusion in the crystallization process. Applying fast scanning calorimetry allows us to link fundamental understanding to industrial application. © 2018 Society of Chemical Industry. © 2018 Society of Chemical Industr

Cross-Linked Bacterial Cellulose Networks Using Glyoxalization

In this study, we demonstrate that bacterial cellulose (BC) networks can be cross-linked via glyoxalization. The fracture surfaces of samples show that, in the dry state, less delamination occurs for glyoxalized BC networks compared to unmodified BC networks, suggesting that covalent bond coupling between BC layers occurs during the glyoxalization process. Young’s moduli of dry unmodified BC networks do not change significantly after glyoxalization. The stress and strain at failure are, however, reduced after glyoxalization. However, the wet mechanical properties of the BC networks are improved by glyoxalization. Raman spectroscopy is used to demonstrate that the stress-transfer efficiency of deformed dry and wet glyoxalized BC networks is significantly increased compared to unmodified material. This enhanced stress-transfer within the networks is shown to be a consequence of the covalent coupling induced during glyoxalization and offers a facile route for enhancing the mechanical properties of BC networks for a variety of applications

Analyzing Protein Denaturation using Fast Differential Scanning Calorimetry

This paper investigates the possibility to measure protein denaturation with Fast Differential Scanning Calorimetry (FDSC). Cancer can be diagnosed by measuring protein denaturation in blood plasma using Differential Scanning Calorimetry (DSC). FDSC can reduce diagnosis time from hours to minutes, requiring significantly smaller sample quantities. To show the feasibility of measuring protein denaturation with FDSC, protein denaturation in human hair is measured. We have been able to observe the phenomena of water evaporation and pyrolysis as they were measured in hair by DSC, however, the protein denaturation peaks are largely obscured by the water evaporation and pyrolysis phenomena, as the current set up only allows dry measurements.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc