Computational Studies of Poly(vinylidene fluoride)

Poly(vinylidene fluoride) (PVDF) is a versatile material with numerous applications, both potential and realized, in many industrial sectors. The extent of applications, ranging from cable and wire products, to sensors for the monitoring of respiration and heart-rate in medicine, indicates on the level of interest the materials science community has for this material. PVDF has the potential to be used in applications where its piezoelectric characteristics are utilized, but for this to be realized, a specific crystal structure, the polar β-phase, need to be present in the material. Since PVDF is polymorphic and usually crystallizes from melt or from solution into the non-polar α-phase, which is of little use in piezoelectric applications, the induction of the β-phase is an active field of research. With computational methods it is possible to study PVDF on a molecular level to gain better insights into the mechanisms behind the formation of this specific crystal structure. Conformational studies of PVDF, the effect of carbon nanotubes on the conformation as well as the mechanical properties of PVDF, copolymerization with trifluoroethylene and the effect of increased temperatures and pressures have been studied using molecular mechanics/dynamics and first principles methods. It has been found that carbon nanotubes mainly act as nucleating agents for the formation of β-phase PVDF as their effect on the mechanical properties of PVDF is relatively small. Furthermore, β-phase formation can be facilitated with very rapid cooling rates from the melt, hindering the transformation into the thermodynamically stable α-phase and by inclusion of trifluoroethylene units in the PVDF chain. With better insights into the mechanism of β-phase PVDF formation, it would ideally be possible to produce piezoelectric PVDF with better characteristics and possibly also in new and more efficient ways

Cykeldäck med automatisk anpassning av dubbfunktion beroende på yttertemperatur

Rapporten är framtagen med ekonomiska bidrag från Trafikverket, Skyltfonden. Ståndpunkter och slutsatser i rapporten reflekterar författaren och överensstämmer inte med nödvändighet med Trafikverkets ståndpunkter och slutsatser inom rapportens ämnesområden.Cyklister är sedan 2008 den grupp som skadas mest i trafiken. Halka eller försämrat väggrepp är ofta en betydelsefull faktor. Antalet cykelolyckor kan potentiellt minska genom användandet av vinterdäck för cyklar. Dubbdäck ger bra fäste på is men ökar cykelns rullmotstånd. Genom att låta dubbarna vila på ett gummimaterial med kraftig variation i hårdhet/styvhet/deformerbarhet vid olika temperaturer skulle man kunna framställa dubbade cykeldäck där metalldubbarnas kontakt med underlaget ändras beroende på temperaturen. Vid minusgrader skall således dubbarnas kontakt med underlaget vara betydligt medan det vid plusgrader skall råda mindre dubbkontakt. Projektet har utvärderat ett antal gummimaterial genom mekaniska tester (ex. hårdhet vid olika temperaturer) och konceptet har demonstrerats i ett proof-of-concept där kontakt med underlag för dubb och däck har utvärderats och friktionstester har genomförts. Temperaturberoende egenskaper för dubbade däck kan erhållas men konceptet måste utvecklas ytterligare då en lägre risk för halka vid rumstemperatur jämfört med vid minusgrader kunde påvisas för samtliga prototyper

Biopolymerer som transportskydd för byggnadsmaterial

Construction materials are exposed to different conditions along the way from the sawmill, during storage and handling, until the materials are a part of the completed construction. During this time the materials may be exposed to moisture and dirt that can cause an attack by moulds. This, in turn, can give rise to health problems for individuals staying in the building and can also be the cause of a bad smell in the building. It is therefore necessary to protect the materials during this limited period of transport, storage, and handling.In this study two construction materials were used; untreated wood and plasterboard. As a possible protection for the materials coatings based on biopolymers were made. Biopolymers are totally degradable and are relatively cheap raw materials. The biopolymers used in this study were starch from potato, protein from corn, and acetylated mono- and diglyceride. Also, fungicides that function as inhibitors for mould growth were added to the coatings.Samples of wood and plasterboard were covered with the coatings using a paint sprayer. The samples were then exposed to a spore suspension containing spores from four of the most common mould species found attacking building material. The samples were then placed in three different climates differing in temperature and humidity. The conditions were in all three cases favourable for mould growth. The samples were placed in these conditions for a month and analysis of the growth on the samples was made once a week and according to a scale with five grades.The results varied very much between the samples, even between samples treated with the same coating, but an obvious trend gave indications of that it is possible to use biopolymers as protection for construction materials. In this study the coating based on the acetylated monoglyceride showed the best properties.Uppsatsnivå:

Effect of a Small Amount of Thermoplastic Starch Blend on the Mechanical Recycling of Conventional Plastics

The usage of bioplastics could increase in the future which may cause contamination of the waste streams of conventional plastics. The objective of this study was to investigate if a small amount of biopolymer contaminating conventional polymers would significantly affect mechanical and thermal properties. A starch-based plastic was first compounded by blending plasticised starch with PLA (polylactic acid). This polymer blend was subsequently compounded with HDPE (high density polyethylene), PP (polypropylene) or PET (polyethylene terephthalate) at 0%, 1% and 5% of the biopolymer. The compounds were characterised by tensile tests, Charpy impact tests, DSC (differential scanning calorimetry) and FESEM (field emission scanning electron microscopy). Tests showed that PE and PP were not significantly affected in terms of tensile strength and modulus but the elongation at break showed a strong reduction. PET was, on the other hand, incompatible with the starch-based plastic. Already at 1% contamination, PET had lost most of its impact strength

Waste Management Option for Bioplastics Alongside Conventional Plastics

Bioplastics can be defined as polymers derived partly or completely from biomass. Bioplastics can be biodegradable such as polylactic acid (PLA) and polyhydroxyalkonoates (PHA); or non-biodegradable (biobased polyethylene (bio-PE), polypropylene (bio-PP), polyethylene terephthalate (bio-PET)). The usage of such bioplastics is expected to increase in the future due to new found interest in sustainable materials. At the same time, these plastics become a new type of waste in the recycling stream. Most countries do not have separate bioplastics collection for it to be recycled or composted. After a brief introduction of bioplastics such as PLA in UK, these plastics are once again replaced by conventional plastics by many establishments due to lack of commercial composting. Recycling companies fear the contamination of conventional plastic in the recycling stream and they said they would have to invest in expensive new equipment to separate bioplastics and recycle it separately. Bioplastics are seen as a threat to the recycling industry as bioplastics may degrade during the mechanical recycling process and the properties of the recycled plastics are seriously impacted. This project studies what happens when bioplastics contaminate conventional plastics. Three commonly used conventional plastics were selected for this study: polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET). In order to simulate contamination, two biopolymers, either polyhydroxyalkanoate (PHA) or thermoplastic starch (TPS) were blended with the conventional polymers. The amount of bioplastics in conventional plastics was either 1% or 5%. The blended plastics were processed again to see the effect of degradation. Mechanical, thermal and morphological properties of these plastics were characterized.   The results from contamination showed that the tensile strength and the modulus of PE was almost unaffected whereas the elongation is clearly reduced indicating the increase in brittleness of the plastic. Generally, it can be said that PP is slightly more sensitive to the contamination than PE. This can be explained by the fact that the melting point of PP is higher than for PE and as a consequence, the biopolymer will degrade more quickly. However, the reduction of the tensile properties for PP is relatively modest. It is also important to notice that when plastics are recovered, there will always be a contamination that will reduce the material properties. The reduction of the tensile properties is not necessary larger than if a non-biodegradable polymer would have contaminated PE or PP. The Charpy impact strength is generally a more sensitive test method towards contamination. Again, PE is relatively unaffected by the contamination but for PP there is a relatively large reduction of the impact properties already at 1% contamination. PET is polyester and it is by its very nature more sensitive to degradation than PE and PP. PET also have a much higher melting point than PE and PP and as a consequence the biopolymer will quickly degrade at the processing temperature of PET. As for the tensile strength, PET can tolerate 1% contamination without any reduction of the tensile strength. However, when the impact strength is examined, it is clear that already at 1% contamination, there is a strong reduction of the properties. It can also be seen that presence of TPS is more detrimental to PET than PHA is. This can be explained by the fact that TPS contain reactive hydroxyl groups that can react with the ester bond of PET. This will in other words lead to degradation of PET. The thermal properties show the change in the crystallinity. As a general conclusion, it can be said that the plastics become less crystalline when contaminated. The blends were also characterized by SEM. Biphasic morphology can be seen as the two polymers are not truly blendable which also contributes to reduced mechanical properties. Recycling of the contaminated polymer shows an increase in crystallinity. This means that when the polymers are processed, polymer degradation occur causing the polymer chains to gradually become shorter which will enhance the crystallization process. The study shows that PE is relatively robust againt contamination, while polypropylene (PP) is somewhat more sensitive and polyethylene terephthalate (PET) can be quite sensitive towards contamination

A molecular-level computational study of the diffusion and solubility of water and oxygen in carbonaceous polyethylene nanocomposites

Monte Carlo and molecular dynamics simulations were performed to investigate the effect on the solubility, diffusion, and permeability of water and oxygen when adding graphene or single-walled carbon nanotubes (SWCNTs) to polyethylene (PE). When compared with pure PE, addition of graphene lowered the solubility of water, whereas at lower temperatures, the oxygen solubility increased because of the oxygen–graphene interaction. Addition of SWCNTs lowered the solubility of both water and oxygen when compared with pure PE. A detailed analysis showed that an ordered structure of PE is induced near the additive surface, which leads to a decrease in the diffusion coefficient of both penetrants in this region. The addition of graphene does not change the permeation coefficient of oxygen (in the direction parallel to the filler) and, in fact, may even increase this coefficient when compared with pure PE. In contrast, the water permeability is decreased when graphene is added to PE. The addition of SWCNTs decreases the permeability of both penetrants. Graphene can consequently be added to selectively increase the solubility and permeation of oxygen over water, at least at lower temperatures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 589–60