Branched polystyrene model systems to investigate the rheology of polymer fiber spinning

The effects of chain topology on the melt- and electrospinning process were investigated in this study for linear and comb polymers. A series of nearly monodisperse model comb structures with well-defined backbone and side chains was synthesized using anionic polymerization of polystyrene. The results indicate a large influence of the polymer topology (length and number of side chains) on the rheological behavior and spinnability of these polymers

Stability of star-shaped RAFT polystyrenes under mechanical and thermal stress

Well-defined three-arm and four-arm star polymers designed via a Z-group approach carrying trithiocarbonate functionalities at the core are prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization featuring molecular weights of Mn{,}SEC = 156 kDa{,} D = 1.16 (3-arm) and Mn{,}SEC = 162 kDa{,} D = 1.15 (4-arm) based on multi-angle laser light scattering (MALLS) detection{,} respectively. The star-shaped polystyrenes are subjected (in bulk) to thermal stress in the temperature range between 140 and 200 [degree]C from 10 minutes up to 96 h. The thermally treated 3-arm and 4-arm star polymers are analyzed via size exclusion chromatography (SEC) to quantify the degradation process at variable temperatures as a function of time under an argon atmosphere. Cleavage rate coefficients of the star polymers are deduced as a function of temperature{,} resulting in activation parameters for the cleavage process{,} i.e. Ea = 131 kJ mol-1; A = 3.93 [times] 1011 s-1 (Mn{,}SEC = 156 kDa{,} D = 1.16{,} 3-arm star) and Ea{,} = 134 kJ mol-1; A = 9.13 [times] 1011 s-1 (Mn{,}SEC = 162 kDa{,} D = 1.15{,} 4-arm star){,} respectively. Processing of the star-shaped polymers is mimicked via a small scale counter rotating twin screw extrusion to achieve nonlinear shear and elongation flow under pressure. Furthermore{,} a rheological assessment via the linear shear deformation region (small amplitude oscillatory shear{,} SAOS) allows for a correlation of the processing conditions with the thermal degradation properties of the star polymers in the melt. Zero shear viscosity ([small eta]0) as a criterion of the degradation process is measured in the rheometer and correlated to the weight-average molecular weight{,} Mw

Polymer crystallinity and crystallization kinetics via benchtop 1 H NMR relaxometry: Revisited method, data analysis, and experiments on common polymers

Semi-crystalline polymers play an enormously important role in materials science, engineering, and nature. Two-thirds of all synthetic polymers have the ability to crystallize which allows for the extensive use of these materials in a variety of applications as molded parts, films, or fibers. Here, we present a study on the applicability of benchtop 1H NMR relaxometry to obtain information on the bulk crystallinity and crystallization kinetics of the most relevant synthetic semi-crystalline polymers. In the first part, we investigated the temperature-dependent relaxation behavior and identified T=Tg+100 K as the minimum relative temperature difference with respect to Tg for which the mobility contrast between crystalline and amorphous protons is sufficient for an unambiguous determination of polymer crystallinity. The obtained bulk crystallinities from 1 H NMR were compared to results from DSC and XRD, and all three methods showed relatively good agreement for all polymers. In the second part, we focused on the determination of the crystallization kinetics, i.e., monitoring of isothermal crystallization, which required a robust design of the pulse sequence, precise temperature calibration, and careful data analysis. We found the combination of a magic sandwich echo (MSE) with a short acquisition time followed by a CarrPurcell-Meiboom-Gill (CPMG) echo train with short pulse timings to be the most suitable for monitoring crystallization. This study demonstrates the application of benchtop 1H NMR relaxometry to investigate the bulk crystallinity and crystallization kinetics of polymers, which can lead to its optimal use as an in situ technique in research, quality control, and processing labs

Polymer crystallinity and crystallization kinetics via benchtop 1 H NMR relaxometry: Revisited method, data analysis, and experiments on common polymers

Semi-crystalline polymers play an enormously important role in materials science, engineering, and nature. Two-thirds of all synthetic polymers have the ability to crystallize which allows for the extensive use of these materials in a variety of applications as molded parts, films, or fibers. Here, we present a study on the applicability of benchtop 1H NMR relaxometry to obtain information on the bulk crystallinity and crystallization kinetics of the most relevant synthetic semi-crystalline polymers. In the first part, we investigated the temperature-dependent relaxation behavior and identified T=Tg+100 K as the minimum relative temperature difference with respect to Tg for which the mobility contrast between crystalline and amorphous protons is sufficient for an unambiguous determination of polymer crystallinity. The obtained bulk crystallinities from 1 H NMR were compared to results from DSC and XRD, and all three methods showed relatively good agreement for all polymers. In the second part, we focused on the determination of the crystallization kinetics, i.e., monitoring of isothermal crystallization, which required a robust design of the pulse sequence, precise temperature calibration, and careful data analysis. We found the combination of a magic sandwich echo (MSE) with a short acquisition time followed by a CarrPurcell-Meiboom-Gill (CPMG) echo train with short pulse timings to be the most suitable for monitoring crystallization. This study demonstrates the application of benchtop 1H NMR relaxometry to investigate the bulk crystallinity and crystallization kinetics of polymers, which can lead to its optimal use as an in situ technique in research, quality control, and processing labs

Radical polymerization of capillary bridges between micron-sized particles in liquid bulk phase as a low temperature route to produce porous solid materials

We present a generic and versatile low-temperature route to produce macroporous bodies with porosity and pore size distribution that are adjustable in a wide range. Capillary suspensions, where the minor fluid is a monomer, are used as precursors. The monomer is preferentially located between the particles, creating capillary bridges, resulting in a strong, percolating network. Thermally induced polymerization of these bridges at temperatures below 100 °C for less than 5 h and subsequent removal of the bulk fluid yields macroscopic, self-supporting solid bodies with high porosity. This process is demonstrated using methyl methacrylate and hydroxyethylmethacrlyate with glass particles as a model system. The produced poly(methyl methacrylate) (PMMA) had a molecular weight of about 500,000 g/mol and dispersity about three. Application specific porous bodies, including PMMA particles connected by PMMA bridges, micron-sized capsules containing phase change material with high inner surface, and porous graphite membranes with high electrical conductivity, are also shown.status: publishe

A novel framework for social life cycle assessment to achieve sustainable cultural tourism destinations

Tourism has a significant multiplier effect on other socioeconomic sectors, leading to improved infrastructure and public services. Its environmental impact, however, remains a subject of concern and there has been a growing emphasis on increasing the sustainability of tourism attractions. Despite the global importance of sustainability evaluation, there are just a few widely accepted methodologies for evaluating it. The life cycle concept is utilised to assess environmental, economic and social impacts and one critical life cycle tool is social life cycle assessment (S-LCA). Tourism-associated activities are ideally suited for the elaboration of data related to social sustainability due to tourism-specific service specifications. As a result, the main question is how can S-LCA help to ensure the long-term viability of cultural tourism destinations. This paper investigates the theoretical evolution of both S-LCA and cultural tourism in order to answer this question. A new framework S-LCA for sustainable cultural tourist destinations is developed and examined, as are potential application gaps. The hypothesized S-LCA conceptual framework S-LCA can thus play an effective role in accomplishing the principles and objectives of sustainable tourism destination management by bringing all stakeholders’ interests together

Linear and Extensional Rheology of Model Branched Polystyrenes: From Loosely Grafted Combs to Bottlebrushes

Monodisperse comb polystyrenes (comb-PS) with loosely to densely grafted architectures up to loosely grafted bottlebrush structures were synthesized via anionic polymerization. This comb-PS series, named PS290-<i>N</i>_br-44, had the same entangled backbone, <i>M</i>_w,bb = 290 kg/mol, corresponding to a number of entanglements along the backbone <i>Z</i>_bb ≅ 20, and similar branch length, <i>M</i>_w,br ≅ 44 kg/mol or <i>Z</i>_br ≅ 3, but varied in the number of branches per molecule, <i>N</i>_br, from 3 to 190 branches. Consequently, the average number of entanglements between two consecutive branch points along the backbone (branch point spacing), <i>Z</i>_s, ranged from well entangled, <i>Z</i>_s ≅ 5, to values that were far less than one entanglement, <i>Z</i>_s ≅ 0.1. Linear viscoelastic data including the zero-shear rate viscosity, η₀, diluted modulus, <i>G</i>_N,s⁰, and a new diluted modulus extracted from the van Gurp–Palmen plot, |<i>G</i>*| at δ = 60°, were analyzed as a function of the <i>M</i>_w of the combs. Scaling of η₀ versus <i>M</i>_w revealed three different regions for increasing <i>N</i>_br or decreasing <i>Z</i>_s: (1) loosely grafted combs with <i>Z</i>_br < <i>Z</i>_s and η₀ ∼ exp­(<i>M</i>_w), (2) densely grafted combs with 1 < <i>Z</i>_s < <i>Z</i>_br and η₀ ∼ <i>M</i>_w^–3.4 followed by η₀ ∼ <i>M</i>_w^–1 for 0.2 < <i>Z</i>_s < 1, and (3) loosely grafted bottlebrushes with <i>Z</i>_s < 0.2 and η₀ ∼ <i>M</i>_w⁵. The relative maximum in η₀ corresponded to a comb-PS with <i><i>Z</i>_<i>s</i></i> ≅ <i>Z</i>_br, and the relative minimum resulted from a comb-PS with <i>Z</i>_s ≅ 0.2, which displayed almost the same η₀ as the linear PS290. Strain hardening factors, SHF ≡ η_E,max/η_DE,max, measured in extensional experiments increased with increasing <i>N</i>_br and reached SHF > 200 for Hencky strains below ε_H = 4, which is tremendously high and has to the best of our knowledge not been observed yet. Such a high strain hardening is of great fundamental and technical importance in extensional processes, e.g., foaming, film blowing, or fiber spinning

Stability of star-shaped RAFT polystyrenes under mechanical and thermal stress

Well-defined three-arm and four-arm star polymers designed via a Z-group approach carrying trithiocarbonate functionalities at the core are prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization featuring molecular weights of Mn,SEC = 156 kDa, D = 1.16 (3-arm) and M n,SEC = 162 kDa, D = 1.15 (4-arm) based on multi-angle laser light scattering (MALLS) detection, respectively. The star-shaped polystyrenes are subjected (in bulk) to thermal stress in the temperature range between 140 and 200 °C from 10 minutes up to 96 h. The thermally treated 3-arm and 4-arm star polymers are analyzed via size exclusion chromatography (SEC) to quantify the degradation process at variable temperatures as a function of time under an argon atmosphere. Cleavage rate coefficients of the star polymers are deduced as a function of temperature, resulting in activation parameters for the cleavage process, i.e. Ea = 131 kJ mol-1; A = 3.93 × 10 11 s-1 (Mn,SEC = 156 kDa, D = 1.16, 3-arm star) and Ea, = 134 kJ mol-1; A = 9.13 × 1011 s-1 (Mn,SEC = 162 kDa, D = 1.15, 4-arm star), respectively. Processing of the star-shaped polymers is mimicked via a small scale counter rotating twin screw extrusion to achieve nonlinear shear and elongation flow under pressure. Furthermore, a rheological assessment via the linear shear deformation region (small amplitude oscillatory shear, SAOS) allows for a correlation of the processing conditions with the thermal degradation properties of the star polymers in the melt. Zero shear viscosity (η0) as a criterion of the degradation process is measured in the rheometer and correlated to the weight-average molecular weight, Mw. This journal is © the Partner Organisations 2014

Polystyrene comb architectures as model systems for the optimized solution electrospinning of branched polymers

The bead to bead-free fibers transition for electrospun filaments was investigated for well-defined linear and comb homopolymers. A series of monodisperse model comb structures with well-defined backbone and side chains was synthesized using anionic polymerization of polystyrene (PS). All model combs had the same backbone and a similar total molecular weight. The length and number of branches was varied, but the total number of monomers in the side chains was nearly constant. Solutions of these polystyrenes in N,N-dimethylformamide (DMF) were electrospun under identical conditions to determine the effect of molecular topology on the morphology of the fibers. The morphology and fiber diameter for all PS model polymers depended on the zero shear viscosity, η0. The comb solutions generally formed fibers at lower η0 and the fibers had larger diameters compared with linear polystyrene. The bead to fiber transition occurred at substantially lower polymer concentrations for combs with fewer, but longer branches

RAFT-based Polystyrene and Polyacrylate Melts under Thermal and Mechanical Stress

Although controlled/living radical polymerization processes have significantly facilitated the synthesis of well-defined low polydispersity polymers with specific functionalities, a detailed and systematic knowledge of the thermal stability of the products–highly important for most industrial processes–is not available. Linear polystyrene (PS) carrying a trithiocarbonate mid-chain functionality (thus emulating the structure of the Z-group approach via reversible addition–fragmentation chain transfer (RAFT) based macromolecular architectures) with various chain lengths (20 kDa ≤ <i>M</i>_n,SEC ≤ 150 kDa, 1.27 ≤ <i>Đ = M</i>_w<i>/M</i>_n ≤ 1.72) and chain-end functionality were synthesized via RAFT polymerization. The thermal stability behavior of the polymers was studied at temperatures ranging from 100 to 200 °C for up to 504 h (3 weeks). The thermally treated polymers were analyzed via size exclusion chromatography (SEC) to obtain the dependence of the polymer molecular weight distribution on time at a specific temperature under air or inert atmospheres. Cleavage rate coefficients of the mid-chain functional polymers in inert atmosphere were deduced as a function of temperature, resulting in activation parameters for two disparate <i>M</i>_n starting materials (<i>E</i>_a = 115 ± 4 kJ<b>·</b>mol^–1, <i>A</i> = 0.85 × 10⁹ ± 1 × 10⁹ s^–1, <i>M</i>_n,SEC = 21 kDa and <i>E</i>_a = 116 ± 4 kJ<b>·</b>mol^–1, <i>A</i> = 6.24 × 10⁹ ± 1 × 10⁹ s^–1, <i>M</i>_n,SEC = 102 kDa). Interestingly, the degradation proceeds significantly faster with increasing chain length, an observation possibly associated with entropic effects. The degradation mechanism was explored in detail via SEC–ESI–MS for acrylate based polymers and theoretical calculations suggesting a Chugaev-type cleavage process. Processing of the RAFT polymers via small scale extrusion as well as a rheological assessment at variable temperatures allowed a correlation of the processing conditions with the thermal degradation properties of the polystyrenes and polyacrylates in the melt