Search

Polymer nanocomposites (NCs) offer outstanding potential for dielectric applications including insulation materials. The large interfacial area introduced by the nanoscale fillers plays a major role in improving the dielectric properties of NCs. Therefore, an effort to tailor the properties of these interfaces can lead to substantial improvement of the material’s macroscopic dielectric response. Grafting electrically active functional groups to the surface of nanoparticles (NPs) in a controlled manner can yield reproducible alterations in charge trapping and transport as well as space charge phenomena in nanodielectrics. In the present study, fumed silica NPs are surface modified with polyurea from phenyl diisocyanate (PDIC) and ethylenediamine (ED) via molecular layer deposition (MLD) in a fluidized bed. The modified NPs are then incorporated into a polymer blend based on polypropylene (PP)/ethylene-octene-copolymer (EOC), and their morphological and dielectric properties are investigated. We demonstrate the alterations in the electronic structure of silica upon depositing urea units using density functional theory (DFT) calculations. Subsequently, the effect of urea functionalization on the dielectric properties of NCs is studied using thermally stimulated depolarization current (TSDC) and broadband dielectric spectroscopy (BDS) methods. The DFT calculations reveal the contribution of both shallow and deep traps upon deposition of urea units onto the NPs. It could be concluded that the deposition of polyurea on NPs results in a bi-modal distribution of trap depths that are related to each monomer in the urea units and can lead to a reduction of space charge formation at filler-polymer interfaces. MLD offers a promising tool for tailoring the interfacial interactions in dielectric NCs.

Although the interest in Mars exploration is growing very rapidly, the availability of materials tailor-made for the Martian environment is limited. The conditions on Mars surface differ significantly from Earth. The density of its atmosphere is significantly lower, resulting in lower pressure and higher temperature range (from -130°C to 30°C). Dust storms consisting of erosive particles are frequent on its surface. The biggest destructive factor is the cosmic radiation, which easily reaches the Martian surface due to the lack of a magnetosphere. A crucial material widely used in engineering is rubber due to its high elastic and damping performance. Rubber returns to its original shape after deformation. This makes it the perfect material for e.g., designing tires, seals, cable covers or dampers for the use in rovers, habitats and space suits. To withstand the harsh environmental conditions, rubber must be properly designed. Up to now, no rubber compound available on the market is able to fulfill the requirements. For this reason, nowadays, the tires of Martian rovers are manufactured from aluminum. Therefore, they do not exhibit the elastic properties resulting in a high transfer of vibrations and wear of the tires caused by dynamic deformation and contact with pointy rocks. Moreover, the rovers need to move at very low speed to minimize dynamic shocks that may damage their sensitive equipment. Thus, they are designed to track only around 100 m a day with a maximum of 0.18 km/h. Application of rubber tires with good damping performance would allow to increase the speed of Martian rovers which enables the exploration without posing a too high threat to the sensitive equipment. Moreover, for future crewed missions and colonization the performance of rovers necessitates the use of rubber to reach higher speed and carry more load with sufficient vibration reduction. To meet the low operating temperatures on Mars a blend of Butadiene Rubber (BR) and Silicone Rubber (VMQ) is used (Tg -100°C, -120°C, respectively) to decrease Tg as much as possible without losing the required properties. BR compounds exhibit high wear resistance, whereas VMQ compounds show very good thermal and aging resistance. Therefore, BR/VMQ blending will be performed to combine their advantageous properties. However, this is a challenging task due to their low chemical compatibility. To overcome this issue, a chemical coupling based on the thiol-ene click reaction between the elastomers is developed. With, this the designed compounds will be ready to face the Martian environmental conditions exhibiting a good elastic performance.

An increasing emphasis of the tire industry on sustainability can be met with new fillers. Based on this, the modification of lignin was developed as it offers abundancy, eco-friendliness and a renewable nature. This study focuses on investigating the reinforcing behavior of a TESPT modified lignin-based filler in a SSBR/BR blend in comparison to CB and silica/TESPT. With mechanical strength comparable to the reference compounds, the lignin-based filler compound exhibits significantly improved dynamic properties. Tailor-made recipes allow to vary the mechanical and dynamic properties to the desired level and to replace conventional fillers.

A new concept for an alternative silica/polymer coupling system was introduced to the tire industry in 2019 to overcome the disadvantage of the current system. If currently the relatively stiff covalent sulfur bridge of the silica/silane/polymer connection is broken, there is no possibility to reconnect. As a consequence, a completely different coupling concept was considered, mimicking the Velcro system known from nature. The tangled and cross-linked rubber macromolecules act as molecular loops and relatively long elastomer brushes grafted on the silica surface act as molecular hooks. The in-rubber properties will be presented to show the efficiency of this new system.

Designing rubber materials that could withstand harsh Martian conditions is a challenging task. Space radiation severely damages the chemical structure of rubber macromolecules, and the low average temperature limits the types of applicable rubber only to those exhibiting very low glass transition temperatures. However, the advantages provided by the unique elastic and dumping properties of rubber have become more attractive in view of the Curiosity rover wheel damage that occurred during the Mars exploration, which was due to the poor elastic performance of the aluminum used for the tires' construction. This triggers the question: is it technologically feasible to develop rubber compounds for Martian rover tires?

Rubber materials exhibit unique viscoelastic properties which deliver advantages for applications involving dynamic deformations and vibrations. They are difficult to replace as sealings, tyres, dumpers, flexible belts and hoses and many more. For the further exploration and planned colonization of Mars such materials are required. However, high ionizing radiation levels resulting from the lack of magnetosphere cause a damage of the chemical structure of rubbers. Low atmospheric pressure may cause vaporization of low molecular rubber additives. Whereas low temperature might reduce the viscoelastic properties of rubber when reaching the level of its glass transition. Therefore, nowadays utilization of rubber materials in Martian landers and rovers is relatively narrow due to their limited durability in Martian environment. For instance, the wheels of Martian rovers are made of alternative materials like aluminium and titanium exhibiting significantly poorer viscoelastic behaviour than rubber, which results in relatively fast wheel damage [1]. This project aims to develop rubber materials for long term utilization on Mars, considering all the influencing features of Martian environment, namely: higher operating temperature range, lower average temperature, lower pressure, ionizing space radiation, higher UV-VIS radiation, inert atmosphere and erosive dust storms. Moreover, the second part of the project will focus on functional mineral fillers preparation from Martian regolith simulant to meet the in-situ resources utilization requirements. The regolith consists of metal and half-metal oxides, which can be processed by a special precipitation method into a high performance nanofiller [2]. References: [1] http://www.planetary.org/blogs/emily-lakdawalla/2014/08190630-curiosity-wheel-damage.html [access: 17 Jul 2019] [2] Sharafudeen, R., Al-Hashim, J.M., Al-Harbi, M.O. et al. Silicon (2017) 9: 917. https://doi.org/10.1007/s12633-016- 9531-8

The silica/silane system is widely used in the rubber industry. A disadvantage of the current system is that once the relatively stiff covalent sulphur bridge of the silica/silane/polymer connection is broken, there is no possibility to reconnect. As a consequence, a completely different coupling concept was considered, mimicking the Velcro-like system known in nature. Following this concept, an alternative type of rubber/silica coupling based on physical entanglements and steric hindrance was developed. The tangled rubber macromolecules act as molecular loops, and relatively long elastomer brushes grafted on the silica surface act as molecular hooks.

Beside carbon black, silica becomes the most important filler for high-performance rubber products. However, unlike carbon black its surface properties are not favorable for providing satisfactory rubber/filler interactions. A significant amount of silanol groups present on the silica surface results in a considerably polar character, whereas most of rubbers exhibit a non-polar or relatively low-polar character. Because of this, various approaches towards different surface treatments of silica were made. Currently, it is state of the art that thesilanization with sulfide-silanes or mercaptosilanes is applied to provide an improved rubber/filler couplingvia sulfur links during vulcanization of rubber. Such solution results in the formation of strong, covalent bonds between the silica surface and rubber macromolecules giving the required performance. However, the covalent, sulfur links are relatively stiff and once broken they are unable to reconnect. Moreover, this type of coupling provides only one type of rubber/filler connections via sulfur chains, therefore not leaving much space for tailoring and modifying the interactions. The aim of this research is to introduce an alternative type of rubber/silica coupling inspired by the velcro system existing in nature. The bio-mimicking mechanism bases on physical entanglements and steric hindrance between tangled rubber macromolecules – acting as molecular loops - and oligomer brushes grafted on the silica surface – acting as molecular hooks. This results in the formation of molecular hooks- and-loops, a rubber/silica interphasefastener.The oligomer brushes were synthesized using a monohydroxy telechelic butadiene oligomercontaining ca. 65 % of monomeric units in vinyl configuration as a backbone, which wasconnected to the silica surface via an isocyanate silane. Afterwards, various thiols were attached to this oligomeric backbone by radical reaction with the vinyl groups of the oligomer. Depending on the chemical structure of the used thiols, these synthesized brushes interact differently with the rubber matrix influencing macroscopic properties of the rubber compound. This approach allows tailoring of rubber/filler interactions by using thiols of various chemical structures as side groups of an oligomer backbone. A major advantage of this coupling system is the possibility to reconnect the rubber/filler physical joints after their detachment. The present work is the first step towards the implementation of a velcro-likefastener as analternative coupling method between rubber and silica.

It is well known that elemental sulfur during heating, at the temperature of about 159C under atmospheric pressure, exhibit an ability to undergo spontaneous ring-opening polymerization. Eight-membered rings (S8), which are the basic form of sulfur under ambient conditions, cleave results in creation of linear sulfur diradicals which polymerize into polymeric form of sulfur. However, sulfur-polymer material obtained from the reaction consists predominantly of unreacted sulfur in form of S8 and contains merely few percent of the polymeric phase. What’s more, in time the content of the polymeric phase slowly decrease due to its instability under ambient conditions. Hence, to obtain a polymeric product it is crucial to stabilize the polymeric phase of sulfur [1-4]. Stabilization of the polymeric phase may be achieved by copolymerization of elemental sulfur with unsaturated organic compounds i.e. dicyclopentadiene, styrene, limonene or 1-3 diisopropenylbenzene via bulk copolymerization process [1,4]. This process was recently described in the literature as “inverse vulcanization”, because of its contrary nature to classic vulcanization of rubber [1]. By following this approach the content of the polymeric phase significantly increases. After extraction of unreacted sulfur, amorphous sulfur/organic copolymers can be used as curing agents for rubber [3], asphalt modifiers [5], sulfur concretes [6] or in various advanced material applications (i.e. Li-S batteries) [1,7,8]. Investigation of thermal properties of sulfur/organic copolymers is essential to investigate the ability to copolymerization between elemental sulfur and particular organic comonomers, as well as to predict their further behavior during processing (i.e. vulcanization of rubber or modification of asphalts at temperatures above 160C). In this work differential scanning calorimetry (DSC) was used to investigate the phase structure of elemental sulfur and sulfur/organic copolymers as well as to track its purification process (extraction of elemental (soluble) sulfur with toluene). Thermogravimetric analysis (TG) was used to determine thermal stability of sulfur/organic copolymers and to confirm that the purification process of sulfur/organic copolymers was performed successfully. [1] W. I. Chung et al., Nat. Chem., 5 (2013) 518 [2] S. Oae, „Organic Chemistry of Sulfur”, Plenum Press, (1977) 33-38 [3] H. Colvin, C. Bull, Jr., Rubb. Chem. Technol., 68 (1995) 746 [4] B. R. Currell et al., „New Uses of Sulfur - Advances in Chemistry”, American Chemical Society, (1975) 1-17 [5] M. Al-Ansary, Innovative solutions for sulphur in Quatar, Proceedings of Sulphur World Symposium in Qatar (2010) [6] N. Ciak, J. Harasymiuk, Sulphur, Technical Sciences, 16 (2013) 323 [7] J. Lim, J. Pyun, K. Char, Angew. Chem. Int. Ed., 54 (2015) 2 [8] A. G. Simmonds et al., ACS Macro Lett., 3 (2014) 229

Although ceramifiable composites have been developed for over 30 years, there is still very broad area for an enhancement of their properties. Following scientific articles in this field, one can find out that since 2013 the number of the papers started to rise significantly [1]. The ceramifiable composites consist of polymer continuous phase and properly designed mix of mineral fillers. Ceramification is an advanced passive flame retardancy process based on formation of continuous ceramic structure on the surface of the composite, which limits transfer of flammable fuel into burning zone as well as oxygen into polymer matrix. Moreover, the ceramic structure provides protection against heat and mechanical stress. In principle, ceramification is improved version of more traditional flame retardancy method based on char formation. However, the ceramic structure formed in ceramification process exhibits outstanding barrier and mechanical properties in comparison to loosely bonded char formed by traditional methods. A key feature characterizing both these methods is lack of toxic or hazardous products formation during flame retardant action. This increases safety of human life and health during a fire accident. Due to silicone elastomers ability to create silica while burning, this group of polymers was firstly selected as continuous phase for ceramifiable composites [2, 3]. The silica created, takes part in the ceramic structure formation, actively improving its properties. On the other hand, silicone rubber exhibits limited ability to incorporate large amount of fillers without a rapid decrease of its mechanical properties. Sufficient amount of mineral fillers is also crucial from the point of view of the ceramification performance. Therefore, recent research in this filed has focused on various organic polymers, much more common in industrial practice and of lower price. Generally, various organic rubbers may be filled with mineral powders up to 300-400 weight parts per hundred parts of their own mass. This allows development of high performance caramifiable composites of much more affordable price. However, high fillers load makes the processability of the composites more challenging, resulting in, for example worse extrudability. This problem must be also addressed in future works. Recently, ethylene-vinyl acetate copolymer (EVA) [4, 5] and styrene-butadiene rubber (SBR) [6] are considered to be the most promising materials for continuous phase for ceramifiable composites. [1] Scopus database, searched words: “ceramifiable” or “ceramizable”, [2] L.G. Hanu, G.P. Simon, J. Mansouri, R.P. Burford, Y.B. Cheng, J. Mater. Process Tech., 153-154 (2004) 401 [3] L.G. Hanu, G.P. Simon, Y.B. Cheng, Mat. Sci. Eng. A, 398 (2005) 180 [4] G. Xinhao, S. Yucai, W. Tingwei, RSC Adv., 6 (2016) 96984 [5] Y-M. Li, C. Deng, Y-Z. Wang, Compos. Sci. Technol., 132 (2016) 116 [6] R. Anyszka, D.M. Bieliński, Z. Pędzich, P. Rybiński, M. Imiela, M. Siciński, M. Zarzecka-Napierała, T. Gozdek, P. Rutkowski P., Materials, 9 (2016) 604

One of the most unique features of polymeric materials is their ability to undergo elastic, reversible deformation. A group of polymers exhibiting such properties owns even an exceptional name – elastomers. The relevance of elastic properties is undeniable in numerous industrial applications form high-performance tyres to seals, gaskets, hoses, cables, and plenty others functional materials manufacturing. However, the hydrocarbon or siloxane macromolecular structure providing elastomeric properties bears also some considerable drawbacks. High flammability is one of the most severe among them. Grand prevalence of polymer materials poses a serious fire threat in households, public, industrial and commercial buildings, as well as mass or private transport vehicles. In order to reduce the fire threat, different approaches with regard to material development and fire-safety are explored. Increase of fire resistance of polymer materials can be provided by chemical modification of the polymer macromolecules or incorporation of flame retardant additives. These additives can be divided according to the mechanism of their action into chemical (suppressing the radical mechanism of fire growth), physical (heat consumption or dissipation, enhancing the polymer/fire barrier interphase) or physicochemical flame retardants. Very often the physical-flame retardants are also called passive-flame retardants due to the fact that they do not generate any harmful products during the fire suppressing mechanism. This makes them more suitable for polymers devoted to applications in densely populated places. One of the most promising paths of increasing the fire resistance of polymers is the development of ceramifiable composites. These materials consist of a polymeric (most often elastomeric) continuous matrix and a properly designed mix of fillers triggering structural conversion under fire/elevated-temperature conditions from elastic composite to brittle ceramics [1]. The ceramic structure formed exhibits continuous morphology and high mechanical and thermal-barrier properties, improving not only fire resistance of the composite but also providing a significant fire/heat protection to the element coated by the composite. Therefore, the interest in these composites is growing considerably. Starting with their utilization as special, fire-resistant cable covers [2-4] and developing into coating for construction-steel elements [5] or anti-ablative materials [6]. The aim of this work is to review current trends in the ceramifiable composites development. Mechanisms of the ceramification phenomena will be presented and discussed, with an emphasis on the latest physical [7] and physicochemical [8] approaches. Tailoring of properties of the composites by functional additives [9, 10] and using new polymers as the composites matrices [11, 12] will also be reviewed. 1. L.G. Hanu, O.P. Simon, J. Mansouri, R.P. Burford and Y.B. Cheng, Journal of Materials Processing Technology 153-154, 401 (2004). 2. S. Hamdani, C. Longuet, J-M. Lopez-Cuesta and F. Ganachaud, Polymer Degradation and Stability 95, 1911 (2010) 3. S. Hamdani-Devarennes, A. Pommier, C. Longuet, J-M. Lopez-Cuesta and F. Ganachaud, Polymer Degradation and Stability 96, 1562 (2011) 4. S. Hamdani-Devarennes, C. Longuet, R. Sonnier, F. Ganachaud and J-M. Lopez-Cuesta, Polymer Degradation and Stability 98, 2021 (2013) 5. B. Gardelle, S. Duquesne, P. Vandereecken and S. Bourbigot, Journal of Fire Sciences 32, 374 (2014) 6. G. Zhang, F. Wang, Z. Huang, J. Dai and M Shi, Materials 9, 723 (2016) 7. X. Zhang, Y. Guan, Y. Xie and D. Qiu, RSC Advances 6, 7970 (2016) 8. S. Hu, F. Chen, J-G. Li, Q. Shen, Z-X Huang and L-M Zhang, Polymer Degradation and Stability 126, 196 (2016) 9. R. Anyszka, D.M. Bielinski, Z. Pedzich and M. Szumera, Journal of Thermal Analysis and Calorimetry 119, 111 (2015). 10. M. Imiela, R. Anyszka, D.M. Bielinski, Z. Pedzich, M. Zarzecka-Napierala and M. Szumera, Journal of Thermal Analysis and Calorimetry 124, 197 (2016). 11. R. Anyszka, D.M. Bielinski, Z. Pedzich, P. Rybinski, M. Imiela, M. Sicinski, M. Zarzecka-Napieraa, T. Gozdek and P. Rutkowski, Materials 9, 604 (2016). 12. H-W. Di, C. Deng, R-M. Li, L-P. Dong and Y-Z. Wang, RSC Advances 5, 51248 (2015)

Beside carbon black, silica becomes the most important filler for high-performance rubber products. However, unlike carbon black its surface properties are not favorable for providing satisfactory rubber/filler interactions. A significant amount of silanol groups present on the silica surface results in a considerably polar character, whereas most of rubbers exhibit a non-polar or relatively low-polar character. Because of this, various approaches towards different surface treatments of silica were made. The aim of this research is to introduce an alternative type of rubber/silica coupling inspired by the velcro system existing in nature. The bio-mimicking mechanism is based on physical entanglements and steric hindrance between mutually soluble (based on calculated solubility parameters): cross-linked and entangled rubber macromolecules – acting as molecular loops - and oligomer brushes grafted onto the silica surface – acting as molecular hooks. This results in the formation of supramolecular hooks-and-loops, a rubber/silica interphase fastener exhibiting reconnectable performance.