Polymers

Research

17 pages, 4996 KiB

Open AccessArticle

Characterization of Rough PTFE Surfaces by the Modified Wilhelmy Balance Technique

by Christian W. Karl, Andrey E. Krauklis, Andrej Lang and Ulrich Giese

Polymers 2020, 12(7), 1528; https://doi.org/10.3390/polym12071528 - 10 Jul 2020

Cited by 6 | Viewed by 4878

The wetting of rough polymer surfaces is of great importance for many technical applications. In this paper, we demonstrate the relationship between the mean roughness values and the fractal dimension of rough and self-affine PTFE surfaces. We have used white light interferometry measurements [...] Read more.

The wetting of rough polymer surfaces is of great importance for many technical applications. In this paper, we demonstrate the relationship between the mean roughness values and the fractal dimension of rough and self-affine PTFE surfaces. We have used white light interferometry measurements to obtain information about the complex topography of the technical surfaces having different height distributions. Two different methods for the calculation of the fractal dimension were used: The height difference correlation function (HDC) and the cube counting method. It was demonstrated that the mean roughness value (R_a) correlates better with the fractal dimension D_f determined by the cube counting method than with the D_f values obtained from HDC calculations. However, the HDC values show a stronger dependency by changing the surface roughness. The advancing and receding contact angles as well as the contact angle hysteresis of PTFE samples of different roughness were studied by the modified Wilhelmy balance technique using deionized water as a liquid. The modified Wilhelmy balance technique enables the possibility for future analysis of very rough PTFE surfaces which are difficult to investigate with the sessile drop method. Full article

(This article belongs to the Special Issue Nordic Polymer Days)

► Show Figures

Graphical abstract

26 pages, 3999 KiB

Open AccessArticle

A Novel Simple Approach to Material Parameters from Commonly Accessible Rheometer Data

by S. Schrüfer, D. Sonnleitner, G. Lang and D. W. Schubert

Polymers 2020, 12(6), 1276; https://doi.org/10.3390/polym12061276 - 3 Jun 2020

Cited by 8 | Viewed by 3213

Abstract

When characterizing the viscoelastic properties of polymers, shear rheological measurements are commonly the method of choice. These properties are known to affect extrusion and nozzle-based processes such as fiber melt spinning, cast film extrusion and 3D-printing. However, an adequate characterization of shear thinning [...] Read more.

When characterizing the viscoelastic properties of polymers, shear rheological measurements are commonly the method of choice. These properties are known to affect extrusion and nozzle-based processes such as fiber melt spinning, cast film extrusion and 3D-printing. However, an adequate characterization of shear thinning polymers can be challenging and still insufficient to not only describe but predict process relevant influences. Furthermore, the evaluation of rheological model systems in literature is mostly based on stress–relaxation experiments, which are rarely available for various polymeric materials. Therefore, a simple approach is presented, that can be used to evaluate and benchmark a wide range of rheological model systems based on commonly accessible frequency sweep data. The approach is validated by analyzing alginate PH176 solutions of various concentrations, a thermoplastic poly-urethane (TPU) Elastollan 1180A melt, the liquid silicon rubber Elastosil 7670 and a polycaprolactone (PCL) fiber-alginate composite system. The used rheological model systems, consisting of simple springs and dashpots, are suitable for the description of complex, viscoelastic material properties that can be observed for polymer solutions and gel-like systems. After revealing a suitable model system for describing those material properties, the determination and evaluation of relevant model parameters can take place. We present a detailed guideline for the systematic parameter revelation using alginate solutions of different concentrations as example. Furthermore, a starting point for future correlations of strut spreading in 3D-bioprinting and model parameters is revealed. This work establishes the basis for a better understanding and potential predictability of key parameters for various fabrication techniques. Full article

(This article belongs to the Special Issue Nordic Polymer Days)

► Show Figures

Figure 1

13 pages, 7002 KiB

Open AccessArticle

Stimuli-Responsive Nanodiamond–Polyelectrolyte Composite Films

by Tony Tiainen, Marina Lobanova, Erno Karjalainen, Heikki Tenhu and Sami Hietala

Polymers 2020, 12(3), 507; https://doi.org/10.3390/polym12030507 - 26 Feb 2020

Cited by 7 | Viewed by 3498

Abstract

Nanodiamonds (NDs) can considerably improve the mechanical and thermal properties of polymeric composites. However, the tendency of NDs to aggregate limits the potential of these non-toxic, mechanically- and chemically-robust nanofillers. In this work, tough, flexible, and stimuli-responsive polyelectrolyte films composed of cross-linked poly(butyl [...] Read more.

Nanodiamonds (NDs) can considerably improve the mechanical and thermal properties of polymeric composites. However, the tendency of NDs to aggregate limits the potential of these non-toxic, mechanically- and chemically-robust nanofillers. In this work, tough, flexible, and stimuli-responsive polyelectrolyte films composed of cross-linked poly(butyl acrylate-co-dimethylaminoethyl methacrylate) (P(BA-co-DMAEMA)) were prepared by photopolymerization. The effects of the added carboxylate-functionalized NDs on their mechanical and stimuli-responsive properties were studied. When the negatively charged NDs were added to the polymerization media directly, the mechanical properties of the films changed only slightly, because of the uneven distribution of the aggregated NDs in the films. In order to disperse and distribute the NDs more evenly, a prepolymerized polycation block copolymer complexing agent was used during the photopolymerization process. This approach improved the mechanical properties of the films and enhanced their thermally-induced, reversible phase-transition behavior. Full article

(This article belongs to the Special Issue Nordic Polymer Days)

► Show Figures

Graphical abstract

17 pages, 4279 KiB

Open AccessArticle

Extrusion of Porous Protein-Based Polymers and Their Liquid Absorption Characteristics

by Antonio J. Capezza, Eva Robert, Malin Lundman, William R. Newson, Eva Johansson, Mikael S. Hedenqvist and Richard T. Olsson

Polymers 2020, 12(2), 459; https://doi.org/10.3390/polym12020459 - 16 Feb 2020

Cited by 20 | Viewed by 3908

Abstract

The production of porous wheat gluten (WG) absorbent materials by means of extrusion processing is presented for the future development of sustainable superabsorbent polymers (SAPs). Different temperatures, formulations, and WG compositions were used to determine a useful protocol that provides the best combination [...] Read more.

The production of porous wheat gluten (WG) absorbent materials by means of extrusion processing is presented for the future development of sustainable superabsorbent polymers (SAPs). Different temperatures, formulations, and WG compositions were used to determine a useful protocol that provides the best combination of porosity and water swelling properties. The most optimal formulation was based on 50 wt.% WG in water that was processed at 80 °C as a mixture, which provided a porous core structure with a denser outer shell. As a green foaming agent, food-grade sodium bicarbonate was added during the processing, which allowed the formation of a more open porous material. This extruded WG material was able to swell 280% in water and, due to the open-cell structure, 28% with non-polar limonene. The results are paving the way towards production of porous bio macromolecular structures with high polar/non-polar liquid uptake, using extrusion as a solvent free and energy efficient production technique without toxic reagents. Full article

(This article belongs to the Special Issue Nordic Polymer Days)

► Show Figures

Graphical abstract

16 pages, 3530 KiB

Open AccessArticle

Morpholino Target Molecular Properties Affect the Swelling Process of Oligomorpholino-Functionalized Responsive Hydrogels

by Eleonóra Parelius Jonášová and Bjørn Torger Stokke

Polymers 2020, 12(2), 268; https://doi.org/10.3390/polym12020268 - 26 Jan 2020

Cited by 1 | Viewed by 2583

Abstract

Responsive hydrogels featuring DNA as a functional unit are attracting increasing interest due to combination of versatility and numerous applications. The possibility to use nucleic acid analogues opens for further customization of the hydrogels. In the present work, the commonly employed DNA oligonucleotides [...] Read more.

Responsive hydrogels featuring DNA as a functional unit are attracting increasing interest due to combination of versatility and numerous applications. The possibility to use nucleic acid analogues opens for further customization of the hydrogels. In the present work, the commonly employed DNA oligonucleotides in DNA-co-acrylamide responsive hydrogels are replaced by Morpholino oligonucleotides. The uncharged backbone of this nucleic acid analogue makes it less susceptible to possible enzymatic degradation. In this work we address fundamental issues related to key processes in the hydrogel response; such as partitioning of the free oligonucleotides and the strand displacement process. The hydrogels were prepared at the end of optical fibers for interferometric size monitoring and imaged using confocal laser scanning microscopy of the fluorescently labeled free oligonucleotides to observe their apparent diffusion and accumulation within the hydrogels. Morpholino-based hydrogels’ response to Morpholino targets was compared to DNA hydrogels’ response to DNA targets of the same base-pair sequence. Non-binding targets were observed to be less depleted in Morpholino hydrogels than in DNA hydrogels, due to their electroneutrality, resulting in faster kinetics for Morpholinos. The electroneutrality, however, also led to the total swelling response of the Morpholino hydrogels being smaller than that of DNA, since their lack of charges eliminates swelling resulting from the influx of counter-ions upon oligonucleotide binding. We have shown that employing nucleic acid analogues instead of DNA in hydrogels has a profound effect on the hydrogel response. Full article

(This article belongs to the Special Issue Nordic Polymer Days)

► Show Figures

Graphical abstract

12 pages, 3585 KiB

Open AccessArticle

The Effect of Extender Particle Size on the Glass Transition Temperature of Model Epoxy Coatings

by Muhammad Ahsan Bashir, Martin Gjerde Jakobsen and Vivian Beate Farstad

Polymers 2020, 12(1), 196; https://doi.org/10.3390/polym12010196 - 12 Jan 2020

Cited by 7 | Viewed by 3199

Abstract

Inorganic extenders are important constituents of 2K thermosetting epoxy-amine coatings and their physical properties play an important role in the final properties of the organic coatings. The effects of extender particle size and loading (i.e., the amount of extender in component A or [...] Read more.

Inorganic extenders are important constituents of 2K thermosetting epoxy-amine coatings and their physical properties play an important role in the final properties of the organic coatings. The effects of extender particle size and loading (i.e., the amount of extender in component A or in the total formulation) on the glass transition temperature (T_g) of model epoxy-amine coatings were studied in this work with differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The obtained results show that the particle size and loading of feldspar particles (from 25 wt% to 70 wt%) do not influence the glass transition temperature of the model epoxy-amine coating significantly. In general, the smaller the particle size the lower the glass transition temperature of the coating but this depression in T_g seems negligible when seen relative to the change in extender particle size. Similar observations are reported for two model coatings having the same lamda (Λ) value but with silica of very different particle sizes (i.e., nanosilica and micron sized silica). Full article

(This article belongs to the Special Issue Nordic Polymer Days)

► Show Figures

Figure 1

18 pages, 2375 KiB

Open AccessArticle

Role of Charge Regulation and Fluctuations in the Conformational and Mechanical Properties of Weak Flexible Polyelectrolytes

by Pablo M. Blanco, Sergio Madurga, Claudio F. Narambuena, Francesc Mas and Josep L. Garcés

Polymers 2019, 11(12), 1962; https://doi.org/10.3390/polym11121962 - 29 Nov 2019

Cited by 18 | Viewed by 2966

Abstract

This work addresses the role of charge regulation (CR) and the associated fluctuations in the conformational and mechanical properties of weak polyelectrolytes. Due to CR, changes in the pH-value modifies the average macromolecular charge and conformational equilibria. A second effect is that, for [...] Read more.

This work addresses the role of charge regulation (CR) and the associated fluctuations in the conformational and mechanical properties of weak polyelectrolytes. Due to CR, changes in the pH-value modifies the average macromolecular charge and conformational equilibria. A second effect is that, for a given average charge per site, fluctuations can alter the intensity of the interactions by means of correlation between binding sites. We investigate both effects by means of Monte Carlo simulations at constant pH-value, so that the charge is a fluctuating quantity. Once the average charge per site is available, we turn off the fluctuations by assigning the same average charge to every site. A constant charge MC simulation is then performed. We make use of a model which accounts for the main fundamental aspects of a linear flexible polyelectrolyte that is, proton binding, angle internal rotation, bond stretching and bending. Steric excluded volume and differentiated treatment for short-range and long-range interactions are also included. This model can be regarded as a kind of “minimal” in the sense that it contains a minimum number of parameters but still preserving the atomistic detail. It is shown that, if fluctuations are activated, gauche state bond probabilities increase and the persistence length decreases, so that the polymer becomes more folded. Macromolecular stretching is also analyzed in presence of CR (the charge depends on the applied force) and without CR (the charge is fixed to the value at zero force). The analysis of the low force scaling behavior concludes that Pincus exponent becomes pH-dependent. Both, with and without CR, a transition from 1/2 at high pH-values (phantom chain) to 3/5 at low pH-values (Pincus regime) is observed. Finally, the intermediate force stretching regime is investigated. It is found that CR induces a moderate influence in the force-extension curves and persistence length (which in this force regime becomes force-dependent). It is thus concluded that the effect of CR on the stretching curves is mainly due to the changes in the average charge at zero force. It is also found that, for the cases studied, the effect of steric excluded volume is almost irrelevant compared to electrostatic interactions. Full article

(This article belongs to the Special Issue Nordic Polymer Days)

► Show Figures

Graphical abstract

12 pages, 2723 KiB

Open AccessArticle

Time–Temperature–Plasticization Superposition Principle: Predicting Creep of a Plasticized Epoxy

by Andrey E. Krauklis, Anton G. Akulichev, Abedin I. Gagani and Andreas T. Echtermeyer

Polymers 2019, 11(11), 1848; https://doi.org/10.3390/polym11111848 - 9 Nov 2019

Cited by 41 | Viewed by 5237

Abstract

Long-term creep properties and the effect of water are important for fiber reinforced polymer (FRP) composite materials used in offshore applications. Epoxies are often used as a matrix material in such composites. A typical design lifetime of offshore FRP structures is 25 or [...] Read more.

Long-term creep properties and the effect of water are important for fiber reinforced polymer (FRP) composite materials used in offshore applications. Epoxies are often used as a matrix material in such composites. A typical design lifetime of offshore FRP structures is 25 or more years in direct contact with water leading to some deterioration of the material properties. Knowing and predicting the extent of the material property deterioration in water is of great interest for designers and users of the offshore FRP structures. It has been established that the time–temperature superposition principle (TTSP) is a useful tool for estimating changes in properties of polymer materials at long times or extreme temperatures. In this work, a time–temperature–plasticization superposition principle (TTPSP) is described and used for predicting the long-term creep behavior of an epoxy compound. The studied epoxy does not degrade chemically via hydrolysis or chain scission but is negatively affected by plasticization with water. The methodology enables prediction of the long-term viscoelastic behavior of amorphous polymers at temperatures below the glass transition (T_g) using short-term creep experimental data. The results also indicate that it is possible to estimate the creep behavior of the plasticized polymer based on the short-term creep data of the respective dry material and the difference between T_g values of dry polymer and plasticized polymer. The methodology is useful for accelerated testing and for predicting the time-dependent mechanical properties of a plasticized polymer below the glass transition temperature. Full article

(This article belongs to the Special Issue Nordic Polymer Days)

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Nordic Polymer Days

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (8 papers)

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI