Joanna Ryszkowska

Thermal and mechanical behaviour of flexible polyurethane foams modified with graphite and phosphorous fillers

Flexible polyurethane foams (FPF) are polymer materials that have high flammability. Fyrol PNX (FPNX) and expandable graphite (EG), have been used to modify the properties of these materials. The aim of this study was to assess the possibility of improving the thermal stability and flame retardancy of FPF by the addition of FPNX and EG fillers. The prepared foams were characterised by their apparent density, hardness, flexibility, irreversible strain and linear flammability, as well as thermogravimetric analysis (TGA), dynamic mechanical analysis, Fourier transform infrared spectroscopy (FT-IR) and pyrolysis combustion flow calorimetry (PCFC) measurements. The apparent density, hardness, flexibility and irreversible strain results showed that the addition of graphite and phosphorous fillers to the FPF makes slight changes to the mechanical properties, which remain within the acceptable norms. It was also observed that reducing the amount of Fyrol PNX and replacing it with the same amount of EG allowed similar values of linear flammability to be obtained with a simultaneous increase in thermal stability, as shown in the TGA study and the PCFC test. Moreover, it was found that the modification of flexible polyurethane foam by the addition of a mixture of FPNX and EG fillers allows the best properties of this type of materials to be obtained. This result indicates that this type of modification could be an effective way to improve the thermal stability of FPF.

Polyurethane foams electrophoretically coated with carbon nanotubes for tissue engineering scaffolds.

Carbon nanotubes (CNTs) were deposited on the surfaces of polyurethane (PUR) foams by electrophoretic deposition (EPD). The parameters of EPD were optimized in order to obtain homogeneous CNT coatings on PUR foams and adequate infiltration of the three-dimensional (3D) porous network. The microstructure of the composites was investigated by high-resolution scanning electron microscopy (HRSEM), revealing that optimal quality of the coatings was achieved by an EPD voltage of 20 V. The thermal properties of the CNT-coated specimens, determined by thermogravimetric analysis (TGA), were correlated to the foam microstructure. In vitro tests in concentrated simulated body fluid (1.5 SBF) were performed to study the influence of the presence of CNTs on the bioactivity of PUR-based scaffolds, assessed by the formation of calcium phosphate (CaP) compounds, e.g. hydroxyapatite (HA), on the foam surfaces. It was observed that CNTs accelerate the precipitation of CaP, which is thought to be due to the presence of more nucleation centres for crystal nucleation and growth, as compared with uncoated foams. Polyurethane foams with CNT coating have the potential to be used as bioactive scaffolds in bone tissue engineering due to their high interconnected porosity, bioactivity and nanostructured surface topography.

Bioactivity of polyurethane-based scaffolds coated with Bioglass®

Polyurethane (PUR) and polyurethane/poly(d, l-lactide) acid (PUR/PDLLA) based scaffolds coated with Bioglass particles for application in bone tissue engineering were fabricated. The slurry-dipping method was used for coating preparation. The homogeneous structure of the Bioglass coatings on the surface of the PUR and PUR/PDLLA foams indicated a good adhesion of the bioactive glass particles to polyurethane without any additional surface treatment. In vitro studies in simulated body fluid (SBF) were performed to study the influence of Bioglass coating on biodegrability and bioactivity of PUR-based scaffolds. The surface of Bioglass-coated samples was covered by a layer of carbonate-containing apatite after 7 days of immersion in SBF, while in uncoated polymer samples apatite crystals were not detected even after 21 days of immersion in SBF. The apatite layer was characterized by scanning electron microscopy (SEM), EDS analysis and attenuated total reflectance-Fourier transform infrared spectrometry (FTIR-ATR). Weight loss measurements showed that the in vitro degradation rate of the composite scaffolds in SBF was higher in comparison to uncoated polyurethane samples. PUR and PUR/PDLLA foams with Bioglass coating have potential to be used as bioactive, biodegradable scaffolds in bone tissue engineering.

Candidate bone-tissue-engineered product based on human-bone-derived cells and polyurethane scaffold.

Biodegradable polyurethanes (PURs) have recently been investigated as candidate materials for bone regenerative medicine. There are promising reports documenting the biocompatibility of selected PURs in vivo and the tolerance of certain cells toward PURs in vitro - potentially to be used as scaffolds for tissue-engineered products (TEPs). The aim of the present study was to take a step forward and create a TEP using human osteogenic cells and a polyurethane scaffold, and to evaluate the quality of the obtained TEP in vivo. Human-bone-derived cells (HBDCs) were seeded and cultured on polyurethane scaffolds in a bioreactor for 14 days. The TEP examination in vitro was based on the evaluation of cell number, cell phenotype and cell distribution within the scaffold. TEPs and control samples (scaffolds without cells) were implanted subcutaneously into SCID mice for 4 and 13 weeks. Explants harvested from the animals were examined using histological and immunohistochemical methods. They were also tested in mechanical trials. It was found that dynamic conditions for cell seeding and culture enable homogeneous distribution, maintaining the proliferative potential and osteogenic phenotype of the HBDCs cultured on polyurethane scaffolds. It was also found that HBDCs implanted as a component of TEP survived and kept their ability to produce the specific human bone extracellular matrix, which resulted in higher mechanical properties of the harvested explants when preseeded with HBDCs. The whole system, including the investigated PUR scaffold and the method of human cell seeding and culture, is recommended as a candidate bone TEP.

Influence of graphite and wood-based fillers on the flammability of flexible polyurethane foams

The aim of this work was to verify the influence of graphite and wood-based fillers on the flammability of flexible polyurethane foams (FPF). Expandable graphite (EG) and cellulose (C) fillers were added to FPFs to improve their thermal stability and reduce their flammability. Four types of foams have been compared: FPF, FPF with the addition of EG, FPF with the addition of C and FPF with the addition of both fillers. Linear flammability tests and pyrolysis combustion flow calorimetry (PCFC) were performed to assess the flammability of these materials. It was found that the addition of cellulose does not improve the fire reaction, but a combination of both the EG and C fillers mixed together was able to achieve a small reduction in flammability, as confirmed by a linear flammability test and PCFC. The best properties observed by PCFC were from FPFs with EG. Usage of cellulose filler separately is not a good method for the assessment of higher thermal stability and lower flammability of FPFs. Thermal properties were measured by thermogravimetric analysis and dynamic mechanical analysis. These results showed that especially EG addition allows to achieve a positive effect on the thermal stability of the tested materials. Mechanical and physical tests (density, hardness, flexibility and irreversible strain) showed that the presence of graphite or cellulose filler results in changes in the properties of the FPFs, but these changes are not extensive. Fourier transform infrared spectroscopy analysis showed that only small changes exist in the chemical structure with the addition of the fillers. The introduction of EG and EG+C fillers into an FPF may reduce its flammability.

The effect of filler chemical constitution and morphological properties on the mechanical properties of natural fiber composites

The purpose of this work was to obtain environmentally friendly natural fibre composites (NFC) from high-density polyethylene (PE-HD) foil and either finely ground sunflower husk or pistachio shells, which both possess physico-mechanical characteristics similar to wood-polymer composite. The composites were prepared from waste materials without the use of additives. It was found that 66% of the sunflower husk grains were from 180 to 850 μm in size, and 88% of the pistachio shell particles were less than 63 μm in size. With the use of a rolling mixer, six mixtures were produced with filler shares amounting to 5, 15 and 30 wt.% of sunflower husk and 15, 35 and 55% of pistachio shell, from which dumbbell-shaped samples were formed via injection processing. The produced materials were analysed for their mechanical properties (impact strength, hardness, tensile strength, Young’s modulus and DMA). The morphologies and chemical composition of the filler as well as the morphological properties of the composites (SEM) were also investigated. The chemical constitution and shape of the filler particles affected the investigated properties of the obtained NFC, and the results were especially significant for the properties of impact strength, stiffness and tensile strength.

Natural fibre composites from polyethylene waste and hazelnut shell: dimensional stability, physical, mechanical and thermal properties

Within the framework of this study, the physical modification of high-density polyethylene waste foil was performed using finely ground hazelnut flour to produce a composite whose physical, mechanical and flammable properties make it possible to use inside and outside of buildings. Three mixtures were produced with filler shares of 11, 26 and 42 vol.% using equipment that is normally used in polymer processing, and no refining additives were applied. The produced materials were analysed for their processing (mass flow ratio), physical (density and moisture content) and mechanical properties (tensile strength, elongation at break and dynamic thermal analysis) and resistance to environmental factors (swelling and water absorption, thermogravimetric analysis and combustion heat). The particle size distribution of the filler and morphological properties of the composites (scanning electron microscopy) were also investigated. It was vital to obtain an inexpensive material with low absorptivity. The resulting materials are characterised by a low density, acceptable low absorptive and good mechanical properties; also, they can constitute an important fuel once their practical properties have been exploited.

Analysis of flammability and smoke emission of rigid polyurethane foams modified with nanoparticles and halogen-free fire retardants

Using one-step method, rigid polyurethane foams were made, modified with developed fire retardant systems containing halogen-free flame retardants and nanofillers in the form of multi-walled carbon nanotubes or nanoscale titanium dioxide. The materials were subjected to a test using a cone calorimeter and smoke-generating chamber, and selected samples were further analyzed via thermogravimetry and oxygen index. Moreover, the products of thermal degradation of selected samples were identified using gas chromatography with mass spectrometer. Conducted flammability tests confirmed the presence of a synergistic effect between the used nanofillers and halogen-free flame retardants. It has been observed that the carbonized layer, the formation of which favored the presence of nanoadditives, inhibits the combustion process. Furthermore, nanofillers influenced favorably reduction in the amount and the number of occurring products of thermal degradation.

Applications of Quantitative Image Analysis to the Description of the Morphology of Boehmite and their Polyurethane Nanocomposites

This paper presents the application of stereology methods to the description of morphological properties of nanoboehmite and its nanocomposites. Images of boemithe, fracture and cut surface of composites were obtained using high-resolution electron microscopy technique and atomic force microscopy. Quantitative analysis of the fracture structure images obtained with HRSEM technique, allowed us to explain the mechanism of changes of mechanical and thermal properties of polyurethane nanocomposites, as well as allowed to determine relationships between structure characteristics and properties of examined materials. Quantitative image analysis was also found to be useful in comparative analysis of polyurethane nanocomposites structure and structure of boehmite and products of its modification.

The Influence of ZrO2 Containing 10% Eu 3+ on the Polyurethane Hard Domain Structure in Nanocomposites with Luminescence Properties

This paper presents the results of studies on ZrO2 containing 10% Eu3+ as a nanofiller in polyurethane nanocomposites with luminescent properties. The nanocomposites, which are potential materials for electro-optical-electronic applications, were prepared by in-situ polymerization. Emission spectra, thermodegradation, thermal analysis and mechanical properties of polyurethane ZrO2/10% Eu3+ were investigated and the structure examined using HRSEM. The aim was to investigate the influence of the distribution of nanofillers in the composite and the structure of hard domains of polyurethanes on the relevant properties for opto-electronic applications.