The flexibility of hybrid silicon-oxide cellulose aerogels was achieved through the formation of thin, uniform silica coatings on cellulose fibres, or local regions of a classical spherical aerogel (Kistler aerogel) combined with areas of less coated cellulose fibres, making use of the flexible properties of the cellulose nanofibres. Furthermore, the inclusion of cellulose during the sol–gel formation allowed the use of traditional freeze-drying instead of CO2 critical point drying as a method for the removal of the liquid phase. The silicon oxide morphologies revealed the possibility of fine-tuning the coating's structure by the choice of the silicon-oxide precursors. Using methyltrimethoxysilane (MTMS) resulted in the formation of classical aerogel or spherical particles, while the use of tetraethyl orthosilicate (TEOS) yielded “pearl-necklace” fibres, and the mix of (3-aminopropyl)triethoxysilane (APTES) with MTMS yielded smooth uniform coatings. The prepared coating morphologies markedly influenced the aerogel's properties (mechanical stiffness/flexibility, flame resistance and hydrophilicity). The silica coatings endured high-temperature exposure and the thermal removal of the cellulose template without substantial morphological changes was confirmed, showing the possibility to use cellulose as an effective template for the synthesis of silicon-oxide nanofibres. The possibility to selectively control aerogel properties already at the synthesis stage, using abundant and renewable materials together with the possibility of using more energy-conservative freeze-drying (rather than critical point drying), is a promising method for more sustainable aerogel preparation towards high-end commercial applications such as electrical fuel cell insulation.

In this study, the stability of nitrocellulose (NC) in the presence of triphenylamine (TPA), Akardite-II (AK-II), and N-Methyl-4-nitroaniline (MNA) was investigated through kinetic modeling and gaseous product analysis. The samples, consisting of pure NC and mixtures, were characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), and differential scanning calorimetry (DSC). The kinetic triplet was determined through iterative iso-conversional methods. The results obtained from TG-DSC revealed that the NC stabilized with TPA exhibited the highest average value of activation energy compared to those stabilized by other stabilizers. The addition of AK-II and MNA altered the decomposition mechanism of NC from the Avrami–Erofeev mechanism to the n-order model, whereas the addition of TPA did not affect the thermal decomposition of NC. FTIR results indicated satisfactory compatibility between the stabilizers and NC. The primary gaseous products of NC and its mixtures were identified under a helium atmosphere. The findings of this study provide guiding principles for the pyrolysis reaction model and storage safety of NC.

Starting from spent coffee grounds, the use of coffee-derived biochar (CB) as a flame retardant (FR) additive was explored following a waste-to-wealth approach. CB was employed alone and in combination with ammonium polyphosphate (APP) and a ternary (Si-Ti-Mg) mixed oxide to enhance the thermal, fire, and mechanical performances of a bisphenol A diglycidyl ether (DGEBA)-based epoxy resin modified with (3-aminopropyl)-triethoxysilane (APTES) and cured with a cycloaliphatic amine hardener. The presence of silicon-modified epoxy chains guaranteed the uniform distribution of CB throughout the resin. The combined FR action of fillers (CB, APP, and Si-Ti-Mg oxide) and the acidic characteristics of hybrid epoxy moieties enabled the achievement of a no dripping UL 94-V-0 classification for epoxy resin containing 20 wt% CB and 1 wt% of phosphorus loading, significantly increasing the flexural modulus (by ∼15%). Although it is not self-extinguishing, compared to pristine resin, the silicon-modified epoxy nanocomposite filled only with CB exhibited a remarkable decrease in the peak of heat release rate (pHRR) (by ∼65%) and a beneficial smoke suppressant effect with a notable decrease (∼11%) in the total smoke production. Cone calorimetry tests, pyrolysis combustion flow calorimetry analysis, and microscopy measurements helped to outline the combined mode of action of CB, APP, and Si-Ti-Mg oxide in the flame retardation of the hybrid epoxy resin, highlighting a strong FR action in the condensed phase, with the formation of a stable aromatic ceramic char, as well as the smoke suppressant character due to the basic nature of the ternary metal oxide and the ability of porous biochar to adsorb the generated gases.

The study aimed to test the hypothesis that biochar's unique properties, such as its microporous structure, can enhance concrete's resilience to high temperatures. Despite expectations of reduced crack formation and enhanced fire resistance, the experimental results revealed a limited impact on concrete's fire behaviour. The investigation involved the use of two biochar types, fine and coarse biochar as replacements for cement and aggregates, respectively. Fine biochar exhibited higher water absorption and Young's modulus than coarse biochar, but both resisted ignition at 35 kW/m2 radiative heat flux and had peak heat release rates below 40 kW/m2. Incorporating these biochars at varying weight percentages (10, 15, and 20 wt.%) into concrete led to a gradual decline in compressive and tensile strength due to reduced binding ability with increased biochar content. Exposure to 1000 °C compromised mechanical properties across all the samples. However, the biochar concrete maintained compressive strength (compared to the control) with up to 20 wt.% biochar as a fine aggregate substitute after exposure to 600 °C, and as a cement replacement after exposure to 200 °C. This substitution also yielded a significant reduction in CO2 emissions (50 % reduction as the biochar loading amount doubled) from concrete manufacturing, showcasing biochar's potential for sustainable construction practices. Despite not fully supporting the initial hypothesis, the study demonstrated biochar's viability in reducing carbon footprint while maintaining concrete strength under certain fire conditions.

This study explores the possibility of using various silsesquioxane precursors such as (3-aminopropyl) triethoxysilane (APTES), methyltrimethoxysilane (MTMS), and tetraethyl orthosilicate (TEOS) to produce silsesquioxane-bacterial cellulose nanofibre (bCNF) aerogels. Each precursor allowed to customize the aerogel properties, leading to unique properties suitable for various applications requiring lightweight insulative materials. When utilizing APTES as the silsesquioxane precursor, an aerogel capable of over 90% recovery after compression was formed, making them suitable for flexible applications. When MTMS was used as the precursor, the aerogel retained some compression recovery (80%) but had the added property of superhydrophobicity with a contact angle over 160° due to the presence of CH3 functional groups, enabling water-repellence. Finally, TEOS allowed for excellent thermal insulative properties with a low Peak Heat Release Rate (PHRR), making it a promising candidate for fire-resistant applications. The customization of these aerogel materials was attributed to a combination of the chemical composition of the silsesquioxane precursors and the morphology of the coated bacterial cellulose nanofibres (bCNF), such as CH3 groups found in MTMS enabled for superhydrophobicity. Differences in morphology, such as uniform and smooth silsesquioxane coatings when using APTES or a “pearl-necklace” morphology using TEOS, enabled either compression recovery and flexibility or low thermal conduction. This investigation of silsesquioxane-bCNF provides a good understanding of the importance of the choice of precursor effect on insulating aerogel properties.

The aim of this project was to find new environmentally friendly, and safe flame retardants(FR) from bio-based resources such as agricultural waste. The intended application of the FRs was on textiles. 

Textiles are used in many different consumer products such as clothes, blankets, carpets, bedsheets, and upholstery, and since they are combustible, they will contribute to a large fire load in a room. One way to increase fire safety in homes and public buildings is to use flame retardants. They can delay the onset of a fire, or reduce the rate of fire spread, which gives opportunity for people to extinguish the fire, or escape in time. However, many flame retardants have been banned because they are bad for the health and/or the environment. 

Phytic acid (PA), which is used by plants to store phosphorus, was combined with a few molecules from the group of purines, which are naturally occurring in living systems, and consequently safe. Commonly known purines are caffeine, theobromine, and theophylline, which are found in coffee, tea and chocolate. Other purines are guanine and adenine, which are building blocks in DNA.

Initially, screening tests were performed where PA and different purines were mixed in various ratios and applied on cotton, polyester, or wool. Burning tests and microscale combustion calorimetry (MCC) were used to assess the FR ability. Based on the results from the screening tests, the best mixtures were selected for further testing. The selected mixtures were PA with theophylline (TP) on cotton, and PA with adenine (AD) on cotton and polyester.

In the second phase of the project, the selected mixtures were investigated with cone calorimetry to get information on their heat release properties, and with thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) to get more detailed information on decomposition temperatures and processes. Nuclear magnetic resonance (NMR) was used to get additional information on the decomposition processes. Scanning electron microscopy (SEM) in combination with energy-dispersive X-ray analysis (EDX) was used to confirm the presence of both PA and purine on the textile, and to compare the surface morphology before and after FR treatment and burning.

Finally, medium scale fire demonstration experiments with a mock-up chair were performed on the best mixture (PA-AD) on cotton and polyester to validate that the small and medium scale experiments are applicable also in scales that are relevant for end-use. 

The mixtures showed overall good FR performance, but the best result was on cotton. The results from methods where milligram size samples were used could be scaled up to fire demonstration tests. The main mechanism of action for the FR was charring the textile surface to reduce the amount of flammable pyrolysis gases, but the FR also worked by forming gases which dilute the oxygen and thus prevents the burning process. Endothermic reactions, e.g., degradation of the material, cools the material so that it will be more difficult to ignite, and formation of free radicals can stop the pyrolysis gases before they can react with the oxygen. Overall, the result was a self-extinguishing FR. The FR can also easily be applied on a textile by dipping the item in an aqueous solution.

Syftet med detta projekt var att hitta nya miljövänliga och säkra flamskyddsmedel (FR) från biobaserade resurser som jordbruksavfall. Den avsedda tillämpningen av FR var på textilier. Textilier används i många olika konsumentprodukter som kläder, filtar, mattor, lakan och klädslar, och eftersom de är brännbara utgör de en stor brandriskfaktor i ett rum. Ett sätt att öka brandsäkerheten i bostäder och offentliga byggnader är att använda flamskyddsmedel. De kan fördröja uppkomsten av en brand, eller minska brandspridningshastigheten, vilket ger möjlighet för människor att släcka branden, eller fly i tid. Många flamskyddsmedel har dock förbjudits eftersom de är dåliga för hälsan och/eller miljön.

Fytinsyra (PA), som används av växter för att lagra fosfor, kombinerades med olika molekylerfrån gruppen puriner, som förekommer naturligt i levande system och därför är säkra. Allmänt kända puriner är koffein, teobromin och teofyllin, som finns i kaffe, te och choklad. Andra puriner är guanin och adenin, som är byggstenar i DNA. Inledningsvis utfördes screeningtester där PA och olika puriner blandades i olika förhållanden och applicerades på bomull, polyester eller ull. Förbränningstester och förbränningskalorimetri i mikroskala (MCC) användes för att bedöma FR-förmågan. Baserat på resultaten från screeningtesterna valdes de bästa blandningarna ut för vidare testning. De utvalda blandningarna var PA med teofyllin (TP) på bomull och PA med adenin (AD) på bomull och polyester.

I den andra fasen av projektet undersöktes de utvalda blandningarna med konkalorimetri för att få information om deras värmeavgivningsegenskaper, och med termogravimetrisk analys (TGA) och differentiell svepkalorimetri (DSC) för att få mer detaljerad information om nedbrytningstemperaturer och processer. Kärnmagnetisk resonans (NMR) användes för att få ytterligare information om nedbrytningsprocesserna. Svepelektronmikroskopi (SEM) i kombination med energidispersiv röntgenanalys (EDX) användes för att bekräfta förekomsten av både PA och purin på textilien, och för att jämföra ytmorfologin före och efter FR-behandling och bränning. Slutligen utfördes medelstora branddemonstrationsexperiment med en mock-up-stol på den bästa blandningen (PA-AD) på bomull och polyester för att validera att de små och medelstora experimenten är tillämpliga även i skalor som är relevanta för slutanvändning.

Blandningarna visade över lag bra flamskyddsprestanda, men det bästa resultatet var på bomull. Resultaten från metoder där prover i milligramstorlek användes kunde skalas upp till branddemonstrationstester. Den huvudsakliga verkningsmekanismen för FR var att förkolna textilytan för att minska mängden brandfarliga pyrolysgaser, men FR fungerade också genom att bilda gaser som späder ut syret och därmed förhindrar förbränningsprocessen. Endoterma reaktioner, t.ex. nedbrytning av materialet, kyler materialet så att det blir svårare att antända, och fria radikaler som bildas kan reagera med pyrolysgaserna innan de kan reagera med syre. Sammantaget blev resultatet en självslocknande FR som också enkelt kan appliceras på textiliergenom att doppa dessa i en vattenlösning.

The aviation sector is continually seeking ways to reduce the weight of aircraft structures without compromising their mechanical integrity. Lightweight materials, such as advanced epoxy sandwich composites with hybrid nanostructures, have the potential to significantly contribute to fuel efficiency, thereby addressing environmental concerns and operational costs. This research investigates the mechanical properties of hybrid sandwich polymer composites filled with silica nanoparticles (SNiPs). Epoxy isocyanate (PU) foam sandwich composites were fabricated with kevlar fiber, carbon fiber, and glass fiber, constructed by alternating inclined interply bidirectional fiber and foam layers. SNiPs were introduced into the composite system at varying percentages, such as 0, 2, 4, and 6 wt%. The study employs a systematic approach, incorporating experimental testing, to assess key mechanical parameters, including tensile strength, flexural strength, and shear strength. The test results indicate that the incorporation of SNiPs improved the mechanical properties of the composites, leading to enhanced strength, toughness, and modulus of elasticity. Incorporation of composite laminates with 4 wt% SiNPs resulted in improved three-point bending, tensile, shear, and torsional strengths, with maximum values of ca. 64, ca. 5, ca. 2 MPa, and ca. 22 Nm, respectively. The findings contribute to the ongoing pursuit of materials that can meet the stringent demands of modern aviation, ultimately paving the way for advancements in aircraft construction and design.