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Papers by Adam Strachota

Gels

Exceptionally fast temperature-responsive, mechanically strong, tough and extensible monolithic n... more Exceptionally fast temperature-responsive, mechanically strong, tough and extensible monolithic non-porous hydrogels were synthesized. They are based on divinyl-crosslinked poly(N-isopropyl-acrylamide) (PNIPAm) intercalated by hydroxypropyl methylcellulose (HPMC). HPMC was largely extracted after polymerization, thus yielding a ‘template-modified’ PNIPAm network intercalated with a modest residue of HPMC. High contents of divinyl crosslinker and of HPMC caused a varying degree of micro-phase-separation in some products, but without detriment to mechanical or tensile properties. After extraction of non-fixed HPMC, the micro-phase-separated products combine superior mechanical properties with ultra-fast T-response (in 30 s). Their PNIPAm network was highly regular and extensible (intercalation effect), toughened by hydrogen bonds to HPMC, and interpenetrated by a network of nano-channels (left behind by extracted HPMC), which ensured the water transport rates needed for ultra-fast des...

Reactive & Functional Polymers, Oct 1, 2019

Nanocomposite polyurethane (PUR) elastomers were synthesized, which contained the heavier, tin-ba... more Nanocomposite polyurethane (PUR) elastomers were synthesized, which contained the heavier, tin-based homologues of POSS ("Sn-POSS"). Most remarkable was the tremendous effect of extremely small Sn-POSS concentrations (around 0.05 wt%) on the glass transition (up-shift by 30-60°C) of the oxidized Sn-POSS/PUR hybrids, which offers the possibility of improving the properties of an important engineering material class (PUR). Important in this context is the hydrogen bonding between the polar segments of Sn-POSS and the carbamate groups of PUR, which was elucidated by NMR. The rigid Sn-POSS cages are of interest due to their specific aggregation behaviour (observed above 5 wt%), and particularly due to their chemical reactivity, which counteracts oxidative degradation of the nanocomposites. This chemical effect of Sn-POSS is strong already at 0.01 wt%. At 0.5 wt%, the properties of the oxidized samples stay close to their initial state before the oxidation. On the other hand, at 'high' Sn-POSS loadings (5-25 wt%), oxidative crosslinking of Sn-POSS with matrix becomes excessive and the oxidized samples are brittle, while also specific heat-induced carbamate-Sn-POSS reactions deteriorate the properties of such oxidized nanocomposites.

Sensors and Actuators B-chemical, 2017

European Polymer Journal, 2017

European Polymer Journal, Aug 1, 2014

A novel tin-based POSS analogue, butylstannoxane dodecamer, was incorporated into epoxy networks ... more A novel tin-based POSS analogue, butylstannoxane dodecamer, was incorporated into epoxy networks with strongly different mesh sizes in comparison to the nanofiller dimensions. The stannoxane cage is especially attractive due to its anti-oxidative effect, which is based on oxidative crosslinking reactions. It can also cause additional reinforcement via nanofiller units' oligomerization. The strongest mechanical reinforcement was observed in nanocomposites with a network mesh width close, but somewhat larger, than was the stannoxane cage size. In the narrow-mesh-matrix, the large rigid nanofiller causes a plastification, due to sterical impossibility of formation of some crosslinks around the filler units. The strongest anti-oxidative effect of the stannoxane was observed in the matrix with the widest mesh, which had the longest polypropylene oxide chains, and hence the largest number of sites potentially reacting with the stannoxane in oxidative crosslinking reactions. The homogeneity of the prepared nanocomposites was evaluated by TEM.

Journal of Analytical and Applied Pyrolysis, 2016

The effect of the dimethylsilyloxy co-monomer "D" on the chemistry of polysiloxane pyrolysis to s... more The effect of the dimethylsilyloxy co-monomer "D" on the chemistry of polysiloxane pyrolysis to silicon oxycarbide (SiOC) glass was studied with the aim of its optimization for the preparation of refractory composites with ceramic fibers. Reasonably small weight losses (shrinkage), but also some temporary plasticity of the material during its pyrolysis was sought. The pyrolysis chemistry was varied by preparing precursors from methyltriethoxysilane (T; main monomer) and dimethyldiethoxysilane (D; co-monomer) in different ratios, but also by using an alternative composition based on tetraethoxysilane (Q) and D. Pyrolysis temperatures between 300 and 1000 • C were studied, and the escaping gases-polar, as well as non-polar-were analysed by means of chromatography/mass spectrometry. It was demonstrated, that the co-monomer D, which undergoes thermal elimination and subsequent reactions with the siloxane skeleton, seems to be responsible for the generally useful "micro-creep" ability of the pyrolyzing material. At higher D contents, where the pyrolysis weight losses strongly increase, the pyrolysis gases were shown to contain also polycyclic oligomers, which consist not only of D, but of the branching T or Q "main" monomers as well. The Si O/Si C exchange reactions of escaping D with the skeleton were found to be highly efficient not only in T/D, but also in Q/D polysiloxanes. It was further found, that the SiOC products after completed pyrolysis at 1000 • C still can release gases detectable by GC/MS upon repeated heating, although no significant weight losses are observed: this indicates the presence of small amounts of pyrolysable sediments in micro-and nano-pores of the SiOC glass.

Procedia structural integrity, 2019

Ceramics matrix composites are rather expensive due to the demanding processing as well as costly... more Ceramics matrix composites are rather expensive due to the demanding processing as well as costly raw materials. Modification of the surface of the fibre is the most common but expensive technique to maximise toughness of CMCs. The prospective method can be a modification of a matrix as was demonstrated for the SiOC matrix reinforced by basalt fibres recently. The partially pyrolysed SiOC matrix based composites at 650°C were used for this study. All production parameters remain the same only reinforcing fibres were different. This work aims at the fibre chemical composition effect on the mechanical properties of composites. The strong effect of the fibres used is observed on the flexural strength values where basalt fibres reaching the level of 800 MPa. The composites reinforced by carbon and R Glass reached 200 MPa and E Glass only 125 MPa. The fracture toughness values correspond well with the flexural strength results which are in a good agreement with the expectations when the defect size is on the comparable level. Two silicate glass fibres with similar chemical composition as basalt fibres, differing mainly in the presence of iron oxides what indicates that iron oxide is responsible for an optimal fibre-matrix bonding in case of basalt fibre reinforced composite.

Key Engineering Materials, Oct 1, 2018

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Ceramics International, Aug 1, 2015

ABSTRACT Polysiloxane resin was used for development of light weight high temperature resistant f... more ABSTRACT Polysiloxane resin was used for development of light weight high temperature resistant foams using the starch foaming technique. The porosity was obtained in the range from 80 to 90%. The pore size effect on the elastic properties was determined and the obtained results were explained with the help of FEM simulation of model situations. The effect of ageing at 1200 °C in air on the density and mechanical properties were determined. The ageing changed slightly the density of foams. The elastic modulus decreased by 15% for the dwell time of 2 h. The extension of the dwell time had no additional effect. The compressive strength related to the density keeps the same trend when ageing is applied. The differences between as received and aged microstructure of foams were explained using SEM analysis.

Journal of The European Ceramic Society, Nov 1, 2020

Two kinds of composite materials reinforced by long unidirectional basalt fibres varying in the m... more Two kinds of composite materials reinforced by long unidirectional basalt fibres varying in the matrix type were studied. The first type of matrix material was prepared by application of partial pyrolysis of polysiloxane preceramic resin at a temperature of 650°C. The second type of matrix material was utilised from cured only polysiloxane and/or epoxy resin and served as reference materials. The advantages of partially pyrolysed composites at elevated temperatures were described recently but the direct comparison with generally used polymer-based composites was not explored deeply. Therefore, both representative materials were characterised with the aim to determine similarities and differences in the fracture processes. The microstructural, elastic and fracture properties were also examined. The fracture resistance was obtained in two typical directions, i.e. along and across the fibres. The fractographic analysis together with fracture characteristics revealed strong and weak aspects of both types of composite materials.

Composites Part B-engineering, Aug 1, 2018

Composites utilising long fibres as reinforcement are the most effective from the point of view o... more Composites utilising long fibres as reinforcement are the most effective from the point of view of the toughening effect. A brittle matrix reinforced by brittle fibres was investigated in this work. Polysiloxane resin was used as matrix precursor in the studied composite, while continuous basalt fibres served as reinforcement. An optimised pyrolysis process conducted at 650°C under nitrogen atmosphere turned the polymeric precursor into the so-called hybrid matrix consisting of nano-domains of pyrolytic SiOC glass and of non-transformed polysiloxane polymer. The pyrolysis temperature of 650°C was found to be optimal, resulting in the fracture toughness attacking the level of 20 MPa.m 1/2 and the strength the value of 1 GPa. The main aim of this paper is to investigate microstructural changes occurring during long-term (1000 hours = 41.7 days) exposition to an oxidative air atmosphere at temperatures from 250°C to 600°C and to describe the effect on the mechanical properties of the studied hybrid-matrix composite. The increasing exposition temperature leads to a significant embrittlement of the composite, while the elastic properties (modulus) remain unchanged. Chemical or microstructural changes in the basalt fibres were not detected after the long-term exposition to the tested high temperatures. Nevertheless, fibre embrittlement can be estimated from the tests. Both matrix and fibre-matrix interface were found to suffer from the applied exposition. Distinct changes in chemical composition as well as in microstructure were observed for the matrix. Hence, the observed embrittlement of the composite can be ascribed partially to the changes in the hybrid matrix and the fibre-matrix interface, and partially to fibre embrittlement.

Polymer Degradation and Stability, Aug 1, 2017

Abstract The chemically active heavier POSS homolog, the n-butylstannoxane dodacamer cage, shows ... more Abstract The chemically active heavier POSS homolog, the n-butylstannoxane dodacamer cage, shows unusual stabilizing properties during an oxidizing treatment of organic-inorganic hybrid polymer materials, into which it is incorporated as nano-building block. In this work, we dispersed Sn_POSS in several matrixes, which mainly had all-carbon backbones (based on polystyrene, polyacrylates and polyethers). Sn_POSS concentration was varied, and it was incorporated either as non-functional cage (blending), or via covalent bonding as a large co-monomer. The stannoxane cages' reactivity in the different matrixes was compared, and the authors propose matrix-dependent mechanisms of the stabilizing effect of Sn_POSS, which make possible to predict the behavior of this cage in different polymers, if their degradation mechanism and eventual reactivity of pendant groups can be estimated. Under oxidizing conditions, the studied matrixes yielded either pendant radicals on (at first) intact chains, or terminal radicals on ends of fragmented chains, depending on the exact polymer structure. The stannoxane cages, if present, subsequently underwent either crosslinking, or chain-repair reactions (fragmented chains re-connection) with the radical sites of the matrix. Another reaction type, which yielded additional crosslinking in the hybrids, was observed in case that the polymer matrix contained suitable pendant functional groups, which were able to react with Sn_POSS after activation either by heat or by oxidation.

Plastics Rubber and Composites, Sep 1, 2011

The main goal of the work was to prepare a cost effective and simple to preform high temperature ... more The main goal of the work was to prepare a cost effective and simple to preform high temperature matrix for composite materials. To fulfil expectations, it was necessary to optimise the design of the composite to have an optimal fibre-matrix interaction. A number of modified polysiloxane resins were studied in various steps of heat treatment. This contribution deals with changes in the behaviour of the matrix as a stay alone material. This knowledge enables the optimisation of composite properties. A fully instrumented indentation technique for the determination of reliable parameters characterising the microstructural changes was used. The fracture behaviour of the prepared composite matrixes was evaluated in terms of indentation cracks. Both optical and scanning electron microscopies were employed in microstructural observations and fracture mechanism qualification.

Ceramics International, Dec 1, 2015

Abstract Polysiloxane foams as precursors to silicon oxycarbide (SiOC) foams were prepared via si... more Abstract Polysiloxane foams as precursors to silicon oxycarbide (SiOC) foams were prepared via simultaneous cure and foaming of liquid methylsiloxane resins, using the relatively environment-friendly ethanol as blowing additive of the boiling-solvent-type, and concentrated aqueous ammonia as catalyst. In order to achieve foam regularity, siloxane-based surfactants were added, and bubble nucleation by mechanical stirring was performed. The precursor foams were subsequently pyrolysed in nitrogen at 1000 °C, yielding SiOC foams as end products. The properties of the latter were fine-tuned during the foaming of the precursors, by the amount of added ethanol and by the time of mechanical stirring prior to foaming. The so-obtained SiOC foams displayed densities of 0.17–0.42 g/cm −3 , corresponding to macro-porosities of 91–79%, compressive strength of 1–6 MPa, and elastic moduli of 0.2–1.6 GPa.

European Polymer Journal, Nov 1, 2019

Super-porous hydrogels were prepared, which are able of fast to ultra-fast volume response to tem... more Super-porous hydrogels were prepared, which are able of fast to ultra-fast volume response to temperature and to pH, and thus show a promise as soft actuators. The hydrogels are based on the poly(N-isopropylacrylamide) (PNIPAm)/silica nanocomposite, in which the filler strongly raises the modulus and also stabilizes the pore walls against collapse during deswelling. The well-interconnected sub-millimetre-sized porosity was generated via solvent freezing during synthesis. The gels morphology makes possible both ultra-fast deswelling and re-swelling (5.5 s for 70% in both directions, in response to T). This work focused on introducing pH-responsiveness into the gels. To this end, 1-10 mol% of sodium methacrylate (SMA) were incorporated as co-monomer. Distinct pHresponsiveness was achieved already at 1 mol% of SMA. Increase of SMA content markedly expands the temperature range of the pH-responsiveness and raises its amplitude. At the same time the increase of SMA content reduces the amplitude of the T-responsiveness, which is only moderate at 10 mol% SMA. The rate of pH-response was found to be always slower than in case of the T-response: 75 s are needed for 70% of de-swelling, and 90 min for 70% of re-swelling. The vast difference in the rates of pH-and T-response can be explained by different mechanisms of stimulus propagation (momentum transfer for T, vs. diffusion for pH) and by the mechanical effect of a contracting stiff and porous surface layer (much faster pH-deswelling than re-swelling). More generally, in case of the pH-stimulus, the mechanistic limits of its propagation in 'simple' porous gels become evident.

Materials and Manufacturing Processes, Oct 19, 2009

A one-step bulk polymerization procedure was used to prepare polyurethane (PUR) materials based o... more A one-step bulk polymerization procedure was used to prepare polyurethane (PUR) materials based on hexamethylene diisocyanate, 1,4-butanediol, and a macrodiol. Polycarbonate diol, polyoxypropylene diol, and polybutadiene diol were used as the macrodiols (MW ca 2000), with dibutyltin dilaurate as the catalyst. To evaluate the mechanical properties of the PUR materials, a common tensile test was performed at room temperature and

Journal of Composite Materials, May 10, 2012

Two mixtures of T and D siloxane monomeric components labelled as TxDy (molecular ratio x:y equal... more Two mixtures of T and D siloxane monomeric components labelled as TxDy (molecular ratio x:y equal 3:1 or 4:1) were chosen as matrix precursors for manufacturing Nextel720 reinforced unidirectional composites which, after pyrolysis at 1000 or 1100°C, revealed good endurance in an oxidizing environment up to 1500°C. Vickers hardness of the heat treated (1000–1500°C) samples of pyrolyzed matrices T3D1 and T4D1 are mutually similar (1100–1400 HV0.2) and reach their maximum between 1200–1300°C. Flexural strength of the pyrolyzed composites is 150–170 MPa and 170–250 MPa for T3D1 and T4D1, respectively. After annealing 3 h in air at 1200–1300°C, the strength slightly decreases but similar treatment at 1500°C yields strengths exceeding those of the pyrolyzed material. Shear modulus of the pyrolyzed T4D1 composite is roughly twice that of the T3D1 one (15 GPa vs. 8 GPa) and both increase sharply to 22–25 GPa after annealing at 1500°C, which manifests substantial improvement of the matrix properties. Fracture toughness of the composites, as measured by chevron notch test at RT, 550°C, and 1100°C, yields 4–5 MPa.m−1/2 for T3D1 and 3–4 MPa.m−1/2 for T4D1. For both composite types, the fracture toughness drops by 1 MPa.m−1/2 when measured at 550°C, which can be attributed to suppression of fibre pull-out due to stress state changes caused by the coefficient of thermal expansion (CTE) mismatch. Fracture surfaces generated during flexural tests of the annealed samples reveal decreasing occurrence of pullout towards the highest annealing temperature.

Polymer Chemistry, 2019

Amphiphilic triblock terpolymers have attractive applications in the preparation of nanoparticles... more Amphiphilic triblock terpolymers have attractive applications in the preparation of nanoparticles with controlled morphology. An additional level of morphology control can be provided by reactive blocks, whose interactions with the solvent vary under different stimuli. In this work, we synthesized a triblock terpolymer (poly(acrylic acid)-b-poly(4-hydroxystyrene)-b-poly{1-[4-(1-methyl-1,2-dicarba-closododecaborane-2-yl methyl)-phenyl]ethylene}) (PAA-b-PHS-b-PSC) containing carboranes as pendant groups by reversible addition fragmentation chain transfer (RAFT) polymerization and subsequently studied its behavior in aqueous solution. Once the nanoparticles were formed, the solubility of the second and third blocks was changed via pH and CsF reactions, respectively. The resulting micelles work as an ON/OFF system, using changes in fluorescence intensity at different pH values.

Ceramics International, Aug 1, 2015

Mechanically strong SiOC foams were prepared via pyrolysis of polysiloxane composites, into which... more Mechanically strong SiOC foams were prepared via pyrolysis of polysiloxane composites, into which 20-70 wt% of epoxy powder were incorporated as sacrificial filler. The chosen epoxy filler degrades practically quantitatively during the pyrolysis in nitrogen, due to a high content of polyoxypropylene chains. The pyrolysis of the composite precursors yielded SiOC foams with apparent densities between 1.31 and 0.62 g/cm 3 , which corresponded to macro-porosities of 35-69%. A hierarchical porosity was obtained due to a relatively wide distribution of the sacrificial filler grains' size. Compressive strength between 15 and 38 MPa was achieved, depending on the apparent density of the SiOC foams: the best result was obtained for the foam with 56% porosity. In the case of denser foams, their strength was reduced by the presence of pyrolysis cracks, while at 70% porosity, the thinner pore walls led to a reduced strength. The elastic modulus of the most promising foam (56% porosity) was found to be 10 GPa.

Soft Matter, 2019

13 C-NMR analysis of the gels' composition SI-Fig. 1: 13 C-NMR spectrum (solid state, dried sampl... more 13 C-NMR analysis of the gels' composition SI-Fig. 1: 13 C-NMR spectrum (solid state, dried sample) of an exemplary poly(NIPAm-cosodium methacrylate) gel intercalated by starch (31.2 wt.% in dry gel).

Gels

Exceptionally fast temperature-responsive, mechanically strong, tough and extensible monolithic n... more Exceptionally fast temperature-responsive, mechanically strong, tough and extensible monolithic non-porous hydrogels were synthesized. They are based on divinyl-crosslinked poly(N-isopropyl-acrylamide) (PNIPAm) intercalated by hydroxypropyl methylcellulose (HPMC). HPMC was largely extracted after polymerization, thus yielding a ‘template-modified’ PNIPAm network intercalated with a modest residue of HPMC. High contents of divinyl crosslinker and of HPMC caused a varying degree of micro-phase-separation in some products, but without detriment to mechanical or tensile properties. After extraction of non-fixed HPMC, the micro-phase-separated products combine superior mechanical properties with ultra-fast T-response (in 30 s). Their PNIPAm network was highly regular and extensible (intercalation effect), toughened by hydrogen bonds to HPMC, and interpenetrated by a network of nano-channels (left behind by extracted HPMC), which ensured the water transport rates needed for ultra-fast des...

Reactive & Functional Polymers, Oct 1, 2019

Nanocomposite polyurethane (PUR) elastomers were synthesized, which contained the heavier, tin-ba... more Nanocomposite polyurethane (PUR) elastomers were synthesized, which contained the heavier, tin-based homologues of POSS ("Sn-POSS"). Most remarkable was the tremendous effect of extremely small Sn-POSS concentrations (around 0.05 wt%) on the glass transition (up-shift by 30-60°C) of the oxidized Sn-POSS/PUR hybrids, which offers the possibility of improving the properties of an important engineering material class (PUR). Important in this context is the hydrogen bonding between the polar segments of Sn-POSS and the carbamate groups of PUR, which was elucidated by NMR. The rigid Sn-POSS cages are of interest due to their specific aggregation behaviour (observed above 5 wt%), and particularly due to their chemical reactivity, which counteracts oxidative degradation of the nanocomposites. This chemical effect of Sn-POSS is strong already at 0.01 wt%. At 0.5 wt%, the properties of the oxidized samples stay close to their initial state before the oxidation. On the other hand, at 'high' Sn-POSS loadings (5-25 wt%), oxidative crosslinking of Sn-POSS with matrix becomes excessive and the oxidized samples are brittle, while also specific heat-induced carbamate-Sn-POSS reactions deteriorate the properties of such oxidized nanocomposites.

Sensors and Actuators B-chemical, 2017

European Polymer Journal, 2017

European Polymer Journal, Aug 1, 2014

A novel tin-based POSS analogue, butylstannoxane dodecamer, was incorporated into epoxy networks ... more A novel tin-based POSS analogue, butylstannoxane dodecamer, was incorporated into epoxy networks with strongly different mesh sizes in comparison to the nanofiller dimensions. The stannoxane cage is especially attractive due to its anti-oxidative effect, which is based on oxidative crosslinking reactions. It can also cause additional reinforcement via nanofiller units' oligomerization. The strongest mechanical reinforcement was observed in nanocomposites with a network mesh width close, but somewhat larger, than was the stannoxane cage size. In the narrow-mesh-matrix, the large rigid nanofiller causes a plastification, due to sterical impossibility of formation of some crosslinks around the filler units. The strongest anti-oxidative effect of the stannoxane was observed in the matrix with the widest mesh, which had the longest polypropylene oxide chains, and hence the largest number of sites potentially reacting with the stannoxane in oxidative crosslinking reactions. The homogeneity of the prepared nanocomposites was evaluated by TEM.

Journal of Analytical and Applied Pyrolysis, 2016

The effect of the dimethylsilyloxy co-monomer "D" on the chemistry of polysiloxane pyrolysis to s... more The effect of the dimethylsilyloxy co-monomer "D" on the chemistry of polysiloxane pyrolysis to silicon oxycarbide (SiOC) glass was studied with the aim of its optimization for the preparation of refractory composites with ceramic fibers. Reasonably small weight losses (shrinkage), but also some temporary plasticity of the material during its pyrolysis was sought. The pyrolysis chemistry was varied by preparing precursors from methyltriethoxysilane (T; main monomer) and dimethyldiethoxysilane (D; co-monomer) in different ratios, but also by using an alternative composition based on tetraethoxysilane (Q) and D. Pyrolysis temperatures between 300 and 1000 • C were studied, and the escaping gases-polar, as well as non-polar-were analysed by means of chromatography/mass spectrometry. It was demonstrated, that the co-monomer D, which undergoes thermal elimination and subsequent reactions with the siloxane skeleton, seems to be responsible for the generally useful "micro-creep" ability of the pyrolyzing material. At higher D contents, where the pyrolysis weight losses strongly increase, the pyrolysis gases were shown to contain also polycyclic oligomers, which consist not only of D, but of the branching T or Q "main" monomers as well. The Si O/Si C exchange reactions of escaping D with the skeleton were found to be highly efficient not only in T/D, but also in Q/D polysiloxanes. It was further found, that the SiOC products after completed pyrolysis at 1000 • C still can release gases detectable by GC/MS upon repeated heating, although no significant weight losses are observed: this indicates the presence of small amounts of pyrolysable sediments in micro-and nano-pores of the SiOC glass.

Procedia structural integrity, 2019

Ceramics matrix composites are rather expensive due to the demanding processing as well as costly... more Ceramics matrix composites are rather expensive due to the demanding processing as well as costly raw materials. Modification of the surface of the fibre is the most common but expensive technique to maximise toughness of CMCs. The prospective method can be a modification of a matrix as was demonstrated for the SiOC matrix reinforced by basalt fibres recently. The partially pyrolysed SiOC matrix based composites at 650°C were used for this study. All production parameters remain the same only reinforcing fibres were different. This work aims at the fibre chemical composition effect on the mechanical properties of composites. The strong effect of the fibres used is observed on the flexural strength values where basalt fibres reaching the level of 800 MPa. The composites reinforced by carbon and R Glass reached 200 MPa and E Glass only 125 MPa. The fracture toughness values correspond well with the flexural strength results which are in a good agreement with the expectations when the defect size is on the comparable level. Two silicate glass fibres with similar chemical composition as basalt fibres, differing mainly in the presence of iron oxides what indicates that iron oxide is responsible for an optimal fibre-matrix bonding in case of basalt fibre reinforced composite.

Key Engineering Materials, Oct 1, 2018

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Ceramics International, Aug 1, 2015

ABSTRACT Polysiloxane resin was used for development of light weight high temperature resistant f... more ABSTRACT Polysiloxane resin was used for development of light weight high temperature resistant foams using the starch foaming technique. The porosity was obtained in the range from 80 to 90%. The pore size effect on the elastic properties was determined and the obtained results were explained with the help of FEM simulation of model situations. The effect of ageing at 1200 °C in air on the density and mechanical properties were determined. The ageing changed slightly the density of foams. The elastic modulus decreased by 15% for the dwell time of 2 h. The extension of the dwell time had no additional effect. The compressive strength related to the density keeps the same trend when ageing is applied. The differences between as received and aged microstructure of foams were explained using SEM analysis.

Journal of The European Ceramic Society, Nov 1, 2020

Two kinds of composite materials reinforced by long unidirectional basalt fibres varying in the m... more Two kinds of composite materials reinforced by long unidirectional basalt fibres varying in the matrix type were studied. The first type of matrix material was prepared by application of partial pyrolysis of polysiloxane preceramic resin at a temperature of 650°C. The second type of matrix material was utilised from cured only polysiloxane and/or epoxy resin and served as reference materials. The advantages of partially pyrolysed composites at elevated temperatures were described recently but the direct comparison with generally used polymer-based composites was not explored deeply. Therefore, both representative materials were characterised with the aim to determine similarities and differences in the fracture processes. The microstructural, elastic and fracture properties were also examined. The fracture resistance was obtained in two typical directions, i.e. along and across the fibres. The fractographic analysis together with fracture characteristics revealed strong and weak aspects of both types of composite materials.

Composites Part B-engineering, Aug 1, 2018

Composites utilising long fibres as reinforcement are the most effective from the point of view o... more Composites utilising long fibres as reinforcement are the most effective from the point of view of the toughening effect. A brittle matrix reinforced by brittle fibres was investigated in this work. Polysiloxane resin was used as matrix precursor in the studied composite, while continuous basalt fibres served as reinforcement. An optimised pyrolysis process conducted at 650°C under nitrogen atmosphere turned the polymeric precursor into the so-called hybrid matrix consisting of nano-domains of pyrolytic SiOC glass and of non-transformed polysiloxane polymer. The pyrolysis temperature of 650°C was found to be optimal, resulting in the fracture toughness attacking the level of 20 MPa.m 1/2 and the strength the value of 1 GPa. The main aim of this paper is to investigate microstructural changes occurring during long-term (1000 hours = 41.7 days) exposition to an oxidative air atmosphere at temperatures from 250°C to 600°C and to describe the effect on the mechanical properties of the studied hybrid-matrix composite. The increasing exposition temperature leads to a significant embrittlement of the composite, while the elastic properties (modulus) remain unchanged. Chemical or microstructural changes in the basalt fibres were not detected after the long-term exposition to the tested high temperatures. Nevertheless, fibre embrittlement can be estimated from the tests. Both matrix and fibre-matrix interface were found to suffer from the applied exposition. Distinct changes in chemical composition as well as in microstructure were observed for the matrix. Hence, the observed embrittlement of the composite can be ascribed partially to the changes in the hybrid matrix and the fibre-matrix interface, and partially to fibre embrittlement.

Polymer Degradation and Stability, Aug 1, 2017

Abstract The chemically active heavier POSS homolog, the n-butylstannoxane dodacamer cage, shows ... more Abstract The chemically active heavier POSS homolog, the n-butylstannoxane dodacamer cage, shows unusual stabilizing properties during an oxidizing treatment of organic-inorganic hybrid polymer materials, into which it is incorporated as nano-building block. In this work, we dispersed Sn_POSS in several matrixes, which mainly had all-carbon backbones (based on polystyrene, polyacrylates and polyethers). Sn_POSS concentration was varied, and it was incorporated either as non-functional cage (blending), or via covalent bonding as a large co-monomer. The stannoxane cages' reactivity in the different matrixes was compared, and the authors propose matrix-dependent mechanisms of the stabilizing effect of Sn_POSS, which make possible to predict the behavior of this cage in different polymers, if their degradation mechanism and eventual reactivity of pendant groups can be estimated. Under oxidizing conditions, the studied matrixes yielded either pendant radicals on (at first) intact chains, or terminal radicals on ends of fragmented chains, depending on the exact polymer structure. The stannoxane cages, if present, subsequently underwent either crosslinking, or chain-repair reactions (fragmented chains re-connection) with the radical sites of the matrix. Another reaction type, which yielded additional crosslinking in the hybrids, was observed in case that the polymer matrix contained suitable pendant functional groups, which were able to react with Sn_POSS after activation either by heat or by oxidation.

Plastics Rubber and Composites, Sep 1, 2011

The main goal of the work was to prepare a cost effective and simple to preform high temperature ... more The main goal of the work was to prepare a cost effective and simple to preform high temperature matrix for composite materials. To fulfil expectations, it was necessary to optimise the design of the composite to have an optimal fibre-matrix interaction. A number of modified polysiloxane resins were studied in various steps of heat treatment. This contribution deals with changes in the behaviour of the matrix as a stay alone material. This knowledge enables the optimisation of composite properties. A fully instrumented indentation technique for the determination of reliable parameters characterising the microstructural changes was used. The fracture behaviour of the prepared composite matrixes was evaluated in terms of indentation cracks. Both optical and scanning electron microscopies were employed in microstructural observations and fracture mechanism qualification.

Ceramics International, Dec 1, 2015

Abstract Polysiloxane foams as precursors to silicon oxycarbide (SiOC) foams were prepared via si... more Abstract Polysiloxane foams as precursors to silicon oxycarbide (SiOC) foams were prepared via simultaneous cure and foaming of liquid methylsiloxane resins, using the relatively environment-friendly ethanol as blowing additive of the boiling-solvent-type, and concentrated aqueous ammonia as catalyst. In order to achieve foam regularity, siloxane-based surfactants were added, and bubble nucleation by mechanical stirring was performed. The precursor foams were subsequently pyrolysed in nitrogen at 1000 °C, yielding SiOC foams as end products. The properties of the latter were fine-tuned during the foaming of the precursors, by the amount of added ethanol and by the time of mechanical stirring prior to foaming. The so-obtained SiOC foams displayed densities of 0.17–0.42 g/cm −3 , corresponding to macro-porosities of 91–79%, compressive strength of 1–6 MPa, and elastic moduli of 0.2–1.6 GPa.

European Polymer Journal, Nov 1, 2019

Super-porous hydrogels were prepared, which are able of fast to ultra-fast volume response to tem... more Super-porous hydrogels were prepared, which are able of fast to ultra-fast volume response to temperature and to pH, and thus show a promise as soft actuators. The hydrogels are based on the poly(N-isopropylacrylamide) (PNIPAm)/silica nanocomposite, in which the filler strongly raises the modulus and also stabilizes the pore walls against collapse during deswelling. The well-interconnected sub-millimetre-sized porosity was generated via solvent freezing during synthesis. The gels morphology makes possible both ultra-fast deswelling and re-swelling (5.5 s for 70% in both directions, in response to T). This work focused on introducing pH-responsiveness into the gels. To this end, 1-10 mol% of sodium methacrylate (SMA) were incorporated as co-monomer. Distinct pHresponsiveness was achieved already at 1 mol% of SMA. Increase of SMA content markedly expands the temperature range of the pH-responsiveness and raises its amplitude. At the same time the increase of SMA content reduces the amplitude of the T-responsiveness, which is only moderate at 10 mol% SMA. The rate of pH-response was found to be always slower than in case of the T-response: 75 s are needed for 70% of de-swelling, and 90 min for 70% of re-swelling. The vast difference in the rates of pH-and T-response can be explained by different mechanisms of stimulus propagation (momentum transfer for T, vs. diffusion for pH) and by the mechanical effect of a contracting stiff and porous surface layer (much faster pH-deswelling than re-swelling). More generally, in case of the pH-stimulus, the mechanistic limits of its propagation in 'simple' porous gels become evident.

Materials and Manufacturing Processes, Oct 19, 2009

A one-step bulk polymerization procedure was used to prepare polyurethane (PUR) materials based o... more A one-step bulk polymerization procedure was used to prepare polyurethane (PUR) materials based on hexamethylene diisocyanate, 1,4-butanediol, and a macrodiol. Polycarbonate diol, polyoxypropylene diol, and polybutadiene diol were used as the macrodiols (MW ca 2000), with dibutyltin dilaurate as the catalyst. To evaluate the mechanical properties of the PUR materials, a common tensile test was performed at room temperature and

Journal of Composite Materials, May 10, 2012

Two mixtures of T and D siloxane monomeric components labelled as TxDy (molecular ratio x:y equal... more Two mixtures of T and D siloxane monomeric components labelled as TxDy (molecular ratio x:y equal 3:1 or 4:1) were chosen as matrix precursors for manufacturing Nextel720 reinforced unidirectional composites which, after pyrolysis at 1000 or 1100°C, revealed good endurance in an oxidizing environment up to 1500°C. Vickers hardness of the heat treated (1000–1500°C) samples of pyrolyzed matrices T3D1 and T4D1 are mutually similar (1100–1400 HV0.2) and reach their maximum between 1200–1300°C. Flexural strength of the pyrolyzed composites is 150–170 MPa and 170–250 MPa for T3D1 and T4D1, respectively. After annealing 3 h in air at 1200–1300°C, the strength slightly decreases but similar treatment at 1500°C yields strengths exceeding those of the pyrolyzed material. Shear modulus of the pyrolyzed T4D1 composite is roughly twice that of the T3D1 one (15 GPa vs. 8 GPa) and both increase sharply to 22–25 GPa after annealing at 1500°C, which manifests substantial improvement of the matrix properties. Fracture toughness of the composites, as measured by chevron notch test at RT, 550°C, and 1100°C, yields 4–5 MPa.m−1/2 for T3D1 and 3–4 MPa.m−1/2 for T4D1. For both composite types, the fracture toughness drops by 1 MPa.m−1/2 when measured at 550°C, which can be attributed to suppression of fibre pull-out due to stress state changes caused by the coefficient of thermal expansion (CTE) mismatch. Fracture surfaces generated during flexural tests of the annealed samples reveal decreasing occurrence of pullout towards the highest annealing temperature.

Polymer Chemistry, 2019

Amphiphilic triblock terpolymers have attractive applications in the preparation of nanoparticles... more Amphiphilic triblock terpolymers have attractive applications in the preparation of nanoparticles with controlled morphology. An additional level of morphology control can be provided by reactive blocks, whose interactions with the solvent vary under different stimuli. In this work, we synthesized a triblock terpolymer (poly(acrylic acid)-b-poly(4-hydroxystyrene)-b-poly{1-[4-(1-methyl-1,2-dicarba-closododecaborane-2-yl methyl)-phenyl]ethylene}) (PAA-b-PHS-b-PSC) containing carboranes as pendant groups by reversible addition fragmentation chain transfer (RAFT) polymerization and subsequently studied its behavior in aqueous solution. Once the nanoparticles were formed, the solubility of the second and third blocks was changed via pH and CsF reactions, respectively. The resulting micelles work as an ON/OFF system, using changes in fluorescence intensity at different pH values.

Ceramics International, Aug 1, 2015

Mechanically strong SiOC foams were prepared via pyrolysis of polysiloxane composites, into which... more Mechanically strong SiOC foams were prepared via pyrolysis of polysiloxane composites, into which 20-70 wt% of epoxy powder were incorporated as sacrificial filler. The chosen epoxy filler degrades practically quantitatively during the pyrolysis in nitrogen, due to a high content of polyoxypropylene chains. The pyrolysis of the composite precursors yielded SiOC foams with apparent densities between 1.31 and 0.62 g/cm 3 , which corresponded to macro-porosities of 35-69%. A hierarchical porosity was obtained due to a relatively wide distribution of the sacrificial filler grains' size. Compressive strength between 15 and 38 MPa was achieved, depending on the apparent density of the SiOC foams: the best result was obtained for the foam with 56% porosity. In the case of denser foams, their strength was reduced by the presence of pyrolysis cracks, while at 70% porosity, the thinner pore walls led to a reduced strength. The elastic modulus of the most promising foam (56% porosity) was found to be 10 GPa.

Soft Matter, 2019

13 C-NMR analysis of the gels' composition SI-Fig. 1: 13 C-NMR spectrum (solid state, dried sampl... more 13 C-NMR analysis of the gels' composition SI-Fig. 1: 13 C-NMR spectrum (solid state, dried sample) of an exemplary poly(NIPAm-cosodium methacrylate) gel intercalated by starch (31.2 wt.% in dry gel).