Dynamic mechanical properties and swelling behavior of Filled Liquid Silicon Rubber

Materials having the properties which are changed with the effect of magnetic fields belong to the group of smart materials and these are known as magnetorheological materials. Liquid Silicon Rubber (LSR) having the applications as liquid or elastomer is present in this group. Magnetorheological property is obtained by filling of liquid Silicon with iron particles. In this study, the influence of concentrations of spherical carbonyl iron particles on both viscoelastic properties and cross-linking behavior of liquid silicon was figured out. Polymer networks were synthesized by reacting of a commercially available chemical namely divinyl Polydimethylsiloxan [(CH3)2SiO]n containing platinum catalyst with a cross-linker namely methyl hydrogen siloxan (CH3(H)Si-O). In the structures of both chemicals, there are nano-silica (SiO2) particles. Rheological characterization of liquid silicon was carried out in a rotational Rheometer by dynamic mechanic test. Enhancement in the cross linking density and acceleration in the polymer network formation rate were observed with increasing temperature. SiO2-Particles/PDMS-Matrix and particle/particle interactions were found to occur with the increasing amount of filler material. In addition, it was observed that relaxation time and hence the frequent dependence of elasticity modulus (G’) was changed. Cross-linking behavior of the elastomer was examined by swelling test, and it was figured out that crosslinking density (interaction at the particle/matrix interface) was increased with the increasing amount of filler material

Dynamic mechanical properties and swelling behavior of Filled Liquid Silicon Rubber

Materials having the properties which are changed with the effect of magnetic fields belong to the group of smart materials and these are known as magnetorheological materials. Liquid Silicon Rubber (LSR) having the applications as liquid or elastomer is present in this group. Magnetorheological property is obtained by filling of liquid Silicon with iron particles. In this study, the influence of concentrations of spherical carbonyl iron particles on both viscoelastic properties and cross-linking behavior of liquid silicon was figured out. Polymer networks were synthesized by reacting of a commercially available chemical namely divinyl Polydimethylsiloxan [(CH3)2SiO]n containing platinum catalyst with a cross-linker namely methyl hydrogen siloxan (CH3(H)Si-O). In the structures of both chemicals, there are nano-silica (SiO2) particles. Rheological characterization of liquid silicon was carried out in a rotational Rheometer by dynamic mechanic test. Enhancement in the cross linking density and acceleration in the polymer network formation rate were observed with increasing temperature. SiO2-Particles/PDMS-Matrix and particle/particle interactions were found to occur with the increasing amount of filler material. In addition, it was observed that relaxation time and hence the frequent dependence of elasticity modulus (G’) was changed. Cross-linking behavior of the elastomer was examined by swelling test, and it was figured out that crosslinking density (interaction at the particle/matrix interface) was increased with the increasing amount of filler material

Avoiding waviness of relaxation spectra

Spectra are material functions, whose different integral transforms yield the measurable rheological quantities in the linear viscoelastic regime. Therefore, their knowledge is of high fundamental interest. However, the calculation of spectra from experimental data is an ill-posed problem. Thus, it is hampered by the problem that a too low density of relaxation modes does not lead to a good description of the input data, while a higher one usually causes a wavy spectrum which cannot be interpreted. To overcome this problem, an additional criterion assuming only gradual changes in the spectrum is introduced allowing for an increase in mode density without an enhanced waviness of the spectrum. This is novel in comparison to previously published spectra algorithms and commercial software packages

Biaxial Elongation Behavior in Partially Molted State of Two-Layer Sheets Containing Postconsumer Material

Due to the lack of raw material and forced by political demand, an increasing percentage of postconsumer materials (PCR) shall be used in all processing methods in polymer technology. Thermoforming, as one of the oldest polymer-processing methods, has special requirements regarding the melt stability at high temperatures. Low melt stability affects the thermoforming in a negative manner, as the low stiffness leads the sheet to sag during the heating phase. In this study, two-layer sheets are used in order to improve melt stability of PCR material. The focus is placed on the influence of rheological properties on the biaxial stretching behavior of mono- and two-layer sheets in partially molted state. In order to create a stabilizing layer, two different thermoformable virgin materials with a melt flow rate (MFR) of 3 g/10 min and 6 g/10 min were chosen. The second layer consists of instable PCR materials with a MFR of 16 g/10min and 50 g/10 min. Rheological investigations, molecular characterization and biaxial stretching tests are used to show the benefit of two-layer sheets for processing PCR material under elongational stress. The results show that the use of two-layer sheets can improve the biaxial stretching properties, so that two-layer sheets can offer a significant potential in the processing of PCR materials in thermoforming

On the Determination of the Enthalpy of Fusion of α‐Crystalline Isotactic Polypropylene Using Differential Scanning Calorimetry, X‐Ray Diffraction, and Fourier‐Transform Infrared Spectroscopy: An Old Story Revisited

The crystallinity determination of polymers using differential scanning calorimetry (DSC) is a standard procedure in industrial and university research. Its value strongly depends on the enthalpy of fusion, which cannot be determined directly using DSC, but must be calibrated using external methods such as X‐ray diffraction (XRD) or density measurements. In addition, the determination of the enthalpy or heat of fusion is not trivial and thus error‐prone; hence, values from 60 to 260 J g−1 are quoted for polypropylene in the literature. It is therefore of great relevance to devise a consistent method to determine the heat of fusion. To determine the heat of fusion for polypropylene, a sample set with a broad range of crystallinities is produced using cooling rates between 1 and ≈3500 K min−1. The melting enthalpy of the samples is determined using DSC measurements. The determination of the melting enthalpy based on XRD measurements is discussed in detail, validated using Fourier‐transform infrared spectroscopy (FTIR), and compared with values quoted in the open literature. Although two different approaches are used to determine the enthalpy of fusion, a value of 170 ± 3 J g−1 is determined

Magneto‐Sensitive Elastomers: An Experimental Point of View

Magneto‐sensitive elastomers (MSEs) are smart materials changing their shape and mechanical properties in the presence of a magnetic field. Focussing on model systems, silicone based MSEs are prepared by a multi‐step mixing process and characterised using a rotational rheometer (plate‐plate). Data obtained by relaxation tests is used to set‐up a material model coupling the theories of viscoelasticity and magnetoelasticity. The behaviour of MSEs in quasi‐static and dynamic mechanical shear experiments can be successfully predicted by the analytical model using parameters received by fitting the transient experiments. The model is validated for small shear deformations (γ = 0.02) and low magnetic fields

Recycling and Reprocessing of Thermoplastic Polyurethane Materials towards Nonwoven Processing

Thermoplastic Polyurethane (TPU) is a unique tailorable material due to the interactions of hard and soft segments within the block-copolymer chain. Therefore, various products can be created out of this material. A general trend towards a circular economy with regards to sustainability in combination with TPU being comparably expensive is of high interest to recycle production as well as post-consumer wastes. A systematic study investigating the property changes of TPU is provided, focusing on two major aspects. The first aspect focuses on characterizing the change of basic raw material properties through recycling. Gel permeation chromatography (GPC) and processing load during extrusion indicate a decrease in molar mass and consequently viscosity with an increasing number of recycling cycles. This leads to a change in morphology at lower molar mass, characterized by differential scanning calorimetry (DSC) and visualized by atomic force microscope (AFM). The change in molar mass and morphology with increasing number of recycling cycles has an impact on the material performance under tensile stress. The second aspect describes processing of the recycled TPU to nonwoven fabrics utilizing melt blowing, which are evaluated with respect to relevant mechanical properties and related to molecular characteristics. The molar mass turns out to be the governing factor regarding mechanical performance and processing conditions for melt blown products