Browsing by Subject "mechanical properties"

Sort by: Order: Results:

Now showing items 1-9 of 9
  • Wan, Ziran (Helsingin yliopisto, 2018)
    The objective of this thesis was to compare the effects of thermal modification under saturated steam and flowing steam on the Scots Pine and the Silver Birch, respectively. One method used in this article complied with the basic principles of traditional ThermoWood process. Treatment temperatures were chosen to be 180℃ and 200℃which are widely used in this method. Super-heated steam and flow-through system were applied in this system. Another one followed the principles as Wood Treatment technology (WTT) developed in Denmark. For this treatment, lower temperatures of 125℃ and 145℃ were applied. The treatment was conducted in a closed system with saturated steam. According to my results, modification under 125℃ saturated steam was ineffective for both Scots Pine and Silver Birch. 200℃ flowing steam is most suitable for the Silver Birch modification. While for the Scots Pine, I would recommend 145℃ saturated steam modification, because under this condition, there is a moderate bending and impact strength reduction but effective anti-swelling efficiency (ASE) improvement. The effects of thermal modification are better on the Silver Birch than the Scots Pine. Modification equipment and chosen of modified specimens need to be considered carefully as they influence the wood properties a lot. In general, mass loss as an indicator value to compare different thermal modification methods is not directly recommended.
  • Rontu, Ville; Nolvi, Anton; Hokkanen, Ari; Haeggström, Edward; Kassamakov, Ivan; Franssila, Sami (2018)
    We have investigated elastic and fracture properties of amorphous Al2O3 thin films deposited by atomic layer deposition (ALD) with bulge test technique using a free-standing thin film membrane and extended applicability of bulge test technique. Elastic modulus was determined to be 115 GPa for a 50 nm thick film and 170 GPa for a 15 nm thick film. Residual stress was 142 MPa in the 50 nm Al2O3 film while it was 116 MPa in the 15 nm Al2O3 film. Density was 3.11 g cm(-3) for the 50 nm film and 3.28 g cm(-3) for the 15 nm film. Fracture strength at 100 hPa s(-1) pressure ramp rate was 1.72 GPa for the 50 nm film while for the 15 nm film it was 4.21 GPa, almost 2.5-fold. Fracture strength was observed to be positively strain-rate dependent. Weibull moduli of these films were very high being around 50. The effective volume of a circular film in bulge test was determined from a FEM model enabling future comparison of fracture strength data between different techniques.
  • Pulkkinen, Jukka (Helsingfors universitet, 2011)
    Emulsified films are prepared by drying an emulsion. Polysaccharide based emulsified films consist of film-forming polysaccharide, fat, emulsifier and plasticiser. In the literature review, the materials used in the preparation of polysaccharide based emulsified films were discussed. The review also included a discussion of which factors affect the water barrier and mechanical properties of the emulsified films. The aim of the experimental study was to find out the potential of konjac glucomannan (KGM) and galactoglucomannan (GGM) in emulsified films. The effect of fat type and fat content on the water barrier and mechanical properties of the films were studied. Emulsified films which contained 30% (wt-% of GGM) fat were prepared from beeswax, rapeseed oil and pine wood oil. Fat contents of 10 and 50% were also used for beeswax. Emulsified films were compared with control films that did not contain any fat. The ratio of KGM and GGM used was 1:1. The water vapour permeability (WVP), water vapour transmission rate (WVTR), Young’s modulus, tensile strength and elongation at break were measured. Films were also viewed with a scanning electron microscope (SEM). KGM and GGM were suitable materials for emulsified films. The surfaces of films dried at room temperature were more uniform than those dried at 60 °C. In the SEM images, wax droplets were smaller than oil droplets. The diameter of oil droplets was about 10 ?m and 2–6 ?m for wax droplets. Wax droplets were better entrapped in the film matrix probably due to their smaller size. As expected, best water barrier properties were obtained with films containing 50% beeswax (p < 0.05). WVP of the films decreased when the content of beeswax in the film increased. Films containing 30% oils and 10% beeswax did not differ significantly from the control film in water barrier and in mechanical properties. The lowest Young’s modulus was with 50% beeswax film. The control film was the stiffest and strongest. There were no statistically significant differences in elongation at break between the films. Emulsified films were successfully prepared from KGM and GGM. The water barrier properties of emulsified films were better than those of the control film and still the mechanical properties were rather well maintained.
  • Liu, Xi Jr (Helsingin yliopisto, 2014)
    Jelly candy is produced by forming a gel with gelling agents in starch mould, followed by drying for days at about 45 °C chamber and obtaining the final products. The main ingredients of jelly candy are gelling agents, sweeteners, acidulants, coloring and flavorings. Gelling agents are the indispensable ingredients that give the gelatinous texture. Psyllium husk powder, konjac glucomannan and gellan gum are novel tested in jelly candy as gelling agents which can at the same time increase dietary fiber content of the candies. It was reported that psyllium husk powder and konjac glucomannan made jelly candy less sticky and springy. In this thesis, jelly candies were made with modified potato starch blended with psyllium husk powder, or konjac glucomannan, or gellan gum. The first aim is to study the effect of different contents of gellan gum on jelly candy properties. The second aim is to compare the effect of psyllium husk powder, konjac glucomannan and gellan gum on jelly candy properties. To achieve these goals, rheological properties of jelly candy mass was studied. Mechanical properties, water content and water activity of the jelly candy were analyzed directly after preparation. Mechanical analysis was made again after the jelly candies stored for two weeks. The raw data were analyzed by MATLAB and then computed by PLS. The results showed that, with the increasing of gellan gum content from 0% to 0.8%, hardness, adhesiveness and elasticity of jelly candies increased. At the same time, yield stress, coefficient of consistency and thixotropy of candy mass also increased. Psyllium husk powder and konjac glucomannan decreased hardness, adhesiveness and elasticity of jelly candies when comparing with gellan gum. They also decreased yield stress, coefficient of consistency and thixotropy of candy mass. Furthermore, along with storage, all the jelly candies became harder and stickier. In conclusion, increasing the content of gellan gum helped to make harder and more chewable jelly candies. The stability of gel structure was also increased and the flowing of candy mass became more difficult. When comparing with gellan gum, psyllium husk powder and konjac glucomannan contributed to softer and less chewable jelly candies. They decreased stability of gel structure and made candy mass flowing easily.
  • Zhang, Yiran (Helsingin yliopisto, 2015)
    Toffee is a hard-textured confectionery product which is made by boiling together sugar, milk, and fat to a certain temperature. The aim of this study was to determine the suitability and effect of seven kinds of dairy powders in toffee processing. The recipes based on dry dairy powder content of 8.8% (1st series), and protein content of 3.5% with constant solid content compensated by sucrose (2nd series). Dairy powders used in this research were: skim milk powder (SMP); butter milk powder (BMP); whole milk powder (WMP); lactose-free skim milk powder (LF-SMP); lactose-free whole milk powder (LF-WMP); 40% demineralized whey powder (D40); and 70% demineralized whey powder (D70). Color, mechanical properties, water content, water activity (aw), and glass transition temperature (Tg) of final toffee samples were analyzed. Mechanical properties were examined after one week storage as well. The data obtained were analyzed by MATLAB and SPSS. In both series, toffees made of LF-SMP showed darkest color, and those containing WMP had lightest color. Higher water content and aw in the 2nd series resulted in softer and more sticky toffees than in the 1st series. Increasing content of protein and lactose increased the hardness of toffee in the 1st series. In the 2nd series, sucrose crystals produced gritty texture of toffee, leading to decreasing hardness and stiffness of toffee, but increasing stickiness. After one week storage, all the toffees became harder and more sticky. Toffees made from lactose free dairy powders always showed higher tendency to flow and deformation than the others, indicating the function of lactose in stability of toffee. In conclusion, increasing content of protein and lactose increased the hardness of toffee. Increasing content of protein and reducing sugar led to darker color of toffee. Higher water content and aw decreased hardness, stiffness, and stability of toffee, but increased stickiness. Increasing the content of sucrose decreased the hardness, stiffness, and stability of toffee as well. SMP showed highest suitability among seven kinds of dairy powders in toffee manufacture. BMP and WMP were also possible to be dairy source in the recipe of toffee. Lactose-free milk powder was not a good choice to form stable toffee.
  • Moreau, Ludovic; Boué, Pierre; Serripierri, Agathe; Weiss, Jérôme; Hollis, Dan; Pondaven, Ildut; Vial, Benjamin; Garambois, Stéphane; Larose, Éric; Helmstetter, Agnès; Stehly, Laurent; Hillers, Gregor; Gilbert, Olivier (2020)
    Field data are needed for a better understanding of sea ice decline in the context of climate change. The rapid technological and methodological advances of the last decade have led to a reconsideration of seismic methods in this matter. In particular, passive seismology has filled an important gap by removing the need to use active sources. We present a seismic experiment where an array of 247 geophones was deployed on sea ice, in the Van Mijen fjord near Sveagruva (Svalbard). The array is a mix of 1C and 3C stations with sampling frequencies of 500 and 1000 Hz. They recorded continuously the ambient seismic field in sea ice between 28 February and 26 March 2019. Data also include active acquisitions on 1 and 26 March with a radar antenna, a shaker unit, impulsive sources, and artificial sources of seismic noise. This data set is of unprecedented quality regarding sea ice seismic monitoring, as it also includes thousands of microseismic events recorded each day. By combining passive seismology approaches with specific array processing methods, we demonstrate that the multimodal dispersion curves of sea ice can be calculated without an active source and then used to infer sea ice properties. We calculated an ice thickness, Young's modulus, and Poisson's ratio with values h=543 cm, E=3.90.15 GPa, and nu=0.340.02 on 1 March, and h=583 cm, E=4.4 +/- 0.15 GPa, and nu=0.32 +/- 0.02 on 5 March. These values are consistent with in situ field measurements and observations.
  • Mäkinen, Lauri (Helsingin yliopisto, 2020)
    In recent decades, interest in bio-based materials as substitutes for plastics has grown significantly. Polysaccharides as part of an arsenal of biodegradable, renewable and edible biopolymers have shown great potential as plastic substitutes. Starch has gained some popularity among the polysaccharides as it seems to fit for these purposes surprisingly well despite its weaknesses. This thesis offers an insight into starch as a biopolymer and reviews its film-forming properties and strengths as a film former while pointing out the weaknesses and suggesting strategies to overcome these disadvantages. Modification of starch by focusing on the preparation of cationic and amphoteric starches by etherification and esterification is discussed followed by an insight into the usage of polyols as plasticizers in the starch films and a novel plasticizer used in the starch films will be presented. Lastly, applications and properties of starch-based biopolymer films will be shortly reviewed. The study was built around the commercial modified potato starch-based biopolymer products which are traditionally used as strengthening agents in paper and board industry. The main samples included both cationic and amphoteric liquid like products. For comparison, native potato starch together with a low cationic powder like product were studied alongside the other samples. The aim was on the utilization of these starches in film preparation and to examine the differences between the samples. The composition of the starch products was confirmed by spectral analysis and investigation of the properties of the films concentrated on thermal and mechanical analysis. Additionally, the work presents a novel use of (2,3-dihydroxypropyl) trimethylammonium chloride (DHPTAC) as a plasticizer for potato starch and modified potato starch based biopolymer films. Major outcome from the mechanical analysis was that the mechanical properties of the starch films were clearly dependent on two things: the amount of DHPTAC in the film and degree of the modification of starch. However, the results from the thermal analysis were not so consistent.
  • Saarilahti, Martti (Suomen metsätieteellinen seura, 1982)
  • Hänninen, Tuomas; Tukiainen, Pekka; Svedström, Kirsi; Serimaa, Ritva; Saranpää, Pekka; Kontturi, Eero; Hughes, Mark; Vuorinen, Tapani (2012)