Emma Strömberg

A statistical design of experiments for optimizing the MALDI-TOF-MS sample preparation of polymers. An application in the assessment of the thermo-mechanical degradation mechanisms of poly (ethylene terephthalate).

The sample preparation procedure for MALDI-TOF MS of polymers is addressed in this study by the application of a statistical Design of Experiments (DoE). Industrial poly (ethylene terephthalate) (PET) was chosen as model polymer. Different experimental settings (levels) for matrixes, analyte/matrix proportions and concentrations of cationization agent were considered. The quality parameters used for the analysis were signal-to-noise ratio and resolution. A closer inspection of the statistical results provided the study not only with the best combination of factors for the MALDI sample preparation, but also with a better understanding of the influence of the different factors, individually or in combination, to the signal. The application of DoE for the improvement of the MALDI measure of PET stated that the best combination of factors and levels was the following: matrix (dithranol), proportion analyte/matrix/cationization agent (1/15/1, V/V/V), and concentration of cationization agent (2 g L(-1)). In a second part, multiple processing by means of successive injection cycles was used to simulate the thermo-mechanical degradation effects on the oligomeric distribution of PET under mechanical recycling. The application of MALDI-TOF-MS showed that thermo-mechanical degradation primarily affected initially predominant cyclic species. Several degradation mechanisms were proposed, remarking intramolecular transesterification and hydrolysis. The ether links of the glycol unit in PET were shown to act as potential reaction sites, driving the main reactions of degradation.

Prevention of Biofilm Associated Infections and Degradation of Polymeric Materials Used in Biomedical Applications

Prevention of Biofilm Associated Infections and Degradation of Polymeric Materials Used in Biomedical Applications

Integrating social sustainability in engineering education at the KTH Royal Institute of Technology

Purpose - The purpose of this paper is to investigate what are perceived to be the main challenges associated with the integration of social sustainability into engineering education at the KTH Roy ...

Influence of biofilm contamination on electrical performance of silicone rubber based composite materials

In this research, three kinds of silicone rubber based composite materials, SIR, NSIR and DSIR, were prepared. SIR is the reference silicone rubber without addition of antimicrobial biocide. Two different antimicrobial agents at a concentration of 3 wt% were added to the reference silicone rubber to form the other two types of materials. The materials were inoculated with a fungal spore suspension containing nutrients. Fungal growth could be observed visually in form of spots by naked eye, and biofilm was formed and detected by SEM observation on the surfaces of SIR and NSIR samples, whereas DSIR samples were completely free of the fungal growth. Then the electrical performance of both clean and biofilm contaminated samples, including the surface and volume conductivity, surface flashover voltage and leakage current before flashover, were measured. The obtained results indicate that as compared with SIR base material, the biocides have not changed the surface conductivity and surface flashover voltage of NSIR and DSIR materials. At the same time, the volume conductivity of NSIR remains almost the same as SIR, while that of DSIR increases by about two orders of magnitude. Biofilm could increase the surface conductivity and decrease the surface flashover voltage significantly. The time domain and frequency domain analyses of the leakage currents flowing before flashover event provide useful information on the severity of contamination by biofilm and the eventual risk for surface flashover.

Photo- and thermo-oxidation of polypropylene, recycled polypropylene and polylactide biocomposites in a microenvironment chamber

This work presents and discusses the photo- and thermo-oxidation of some sustainable biocomposites based on biodegradable materials from renewable resources and virgin and recycled petroleum-based polymeric materials as matrix and reinforced with natural fibres. PP/wood flour, recycled PP/cellulose and PLA/wood flour composites were degraded by photo-oxidation in a microenvironment chamber, in parallel thermo-oxidation was performed in a forced-ventilation oven. Physical and chemical property changes were monitored by tensile testing, DSC, FTIR and SEM. Both PPW and recPPcell composites showed deterioration of the mechanical properties after 15 days of thermo-oxidation, indicating that the incorporated natural fibres influenced the thermal stability of the whole composite. PLAW showed a smaller increase in crystallinity (13%) and a decrease in melt temperature than the corresponding neat PLA. The advantages of reinforcement of PLA by natural fibres are shown by the dramatically improved thermal properties of PLAW compared to the neat polymer.

Image Analysis Determination of the Influence of Surface Structure of Silicone Rubbers on Biofouling

This study focuses on how the texture of the silicone rubber material affects the distribution of microbial growth on the surface of materials used for high voltage insulation. The analysis of surface wetting properties showed that the textured surfaces provide higher receding contact angles and therefore lower contact angle hysteresis. The textured surfaces decrease the risk for dry band formation and thus preserve the electrical properties of the material due to a more homogeneous distribution of water on the surface, which, however, promotes the formation of more extensive biofilms. The samples were inoculated with fungal suspension and incubated in a microenvironment chamber simulating authentic conditions in the field. The extent and distribution of microbial growth on the textured and plane surface samples representing the different parts of the insulator housing that is shank and shed were determined by visual inspection and image analysis methods. The results showed that the microbial growth was evenly distributed on the surface of the textured samples but restricted to limited areas on the plane samples. More intensive microbial growth was determined on the textured samples representing sheds. It would therefore be preferable to use the textured surface silicone rubber for the shank of the insulator.

Degradation Behaviour of Natural Fibre Reinforced Starch-Based Composites under Different Environmental Conditions

The purpose of this work was to study the effect of hydrothermal, biological and photo degradation on natural fibres reinforced biodegradable starch-based (Mater-BiKE) composites to characterize th ...

Thermal and thermo-oxidative stability and kinetics of decomposition of PHBV/sisal composites

ABSTRACT The decomposition behaviours of composites made of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and sisal were assessed in terms of thermal stability and decomposition kinetics, under inert and oxidative conditions, by means of multi-rate linear non-isothermal thermogravimetric experiments. A statistical design of experiments was applied to study the influence of the addition of sisal (0–10–20–30%wt), the presence coupling agent (Yes/No) and the applied conditions of work (inert or oxidative). An improvement of the thermal and thermo-oxidative stability of PHBV with the addition of sisal was observed for all cases. An accurate methodology based on iso-conversional methods was applied to simulate the potential of thermal recovery technologies, such as pyrolysis and controlled combustion, to use these biocomposites after the end of their service life. The mathematical descriptions of both thermo-chemical reactions were helpful in the evaluation of the eventual optimal operational conditions to carry out a suitable energetic valorisation. A minimum of 240°C and 137 kJ/mol of activation energy in inert conditions and 236°C and 118 kJ/mol in oxidative conditions ensured the feasibility of the reactions regardless the composition of the PHBV/sisal biocomposites, which may ease the operability of further energy valorisation with the aim to turn biowaste into new fuels.

Use of essential oils for the prevention of biofilm formation on silicone rubber high voltage insulators

The prevention of biofilm formation on high voltage insulators is important to avoid changes in the surface properties of the material and the subsequent failure of the application. Antimicrobial silicone rubber samples were prepared by the addition of thymol and eugenol to Sylgard 184 to determine the possibility of using natural antimicrobial agents present in essential oils in materials used for high voltage insulators. The antimicrobial effects of thymol and eugenol were studied for different fungal strains and for green algae identified in the biofilms formed on insulators in Tanzania, Sri Lanka and Sweden. It was successfully demonstrated that samples containing high amount of eugenol and different concentrations of thymol could inhibit the fungal growth of strains from Sri Lanka and Tanzania and the growth of green algae. The growth of strains from Sweden was also suppressed. The addition of eugenol to the material resulted in a non-crosslinked system and therefore, the antimicrobial effect of the additive in the material could not be assessed. The addition of thymol did not significantly influence the thermal and mechanical properties of Sylgard184. Although thermal analysis revealed that a large amount of the antimicrobial agent was lost during sample preparation, the materials were effective against microbial growth, even at low thymol concentrations.

The effect of surface modifications on the mechanical and thermal properties of empty fruit bunch oil palm fibre PP biocomposites

The aim of this work was to study the effect of chemical surface modifications on empty fruit bunch oil palm fibre/polypropylene composite properties. By FTIR spectra, propionylated fibre and PPgMA-modified fibre showed the presence of a carbonyl group of esters while vinyltrimethoxysilane-treated fibre showed a peak of silicate, confirming that the modifications were successful. PPgMAmodified fibre PP composite at fibre content 20% demonstrated the highest modulus of 0.71 GPa while the modulus of unmodified fibre PP composite was 0.56 GPa. By DSC analysis, PPgMA-modified fibre and vinyltrimethoxysilane-treated fibre PP composite at the same fibre content of 5% showed the highest crystallinity of 46% and 44% respectively whereas unmodified fibre PP composite showed a lower crystallinity of 38%. The DMTA analysis showed that after 60°C, the modified fibre PP composites exhibited a higher stiffness than pure polypropylene.