Browsing by Author "Borůvka, Martin"

Now showing 1 - 13 of 13
  • Thumbnail Image
    Item
    Dynamic-mechanical properties of polymer composites with the short and long glass fibers
    (Trans Tech Publications Ltd, 2016-01-01) Lenfeld, Petr; Běhálek, Luboš; Borůvka, Martin; Průšek, Jan
    Nowadays the use of glass fibers in development of polymer composites creates a very interesting research area aiming to achieve multiple outputs to different applications. The use of thermoplastic composites reinforced with glass fibers in engineering applications like automotive industry has increased considerably in the last few decades. These composites combine high mechanical strength properties, reduced mass, easy processing and corrosion resistance. The shifting from metals to engineering composites pushes towards light weighting benefits which results in improved fuel efficiency. This paper is focused on the assessment of polymer composites properties on the basis of polyamides (PA6.6) with the short (GF) and long glass fibres (LGF). The bulk characterization of all samples has been made by Dynamic Mechanical Analysis (DMA) depending on temperature, stress frequency and the weight percentage of reinforcement in matrix. © 2016 Trans Tech Publications, Switzerland.
  • Thumbnail Image
    Item
    Effect of dielectric barrier discharge plasma surface treatment on the properties of pineapple leaf fiber reinforced poly(Lactic acid) Biocomposites
    (Trans Tech Publications Ltd, 2016-01-01) Borůvka, Martin; Ngaowthong, Chakaphan; Běhálek, Luboš; Habr, Jiří; Lenfeld, Petr
    Plant source-based stiff fiber reinforced bioplastics based on natural plant derived substances show promise of providing degradation back into the environment when they are no longer needed. These "green" composites have enormous potential to replace materials originated from non-renewable resources and may turn out to be one of the material revolutions of this century. Unlike synthetic composites, "green" composites are renewable, carbon neutral, biodegradable, nonpetroleum based, and have low environmental, human health and safety risks. In this paper effect of pineapple leaf fiber (PALF) length and physical surface treatment on to the properties of the composites was investigated at 10% wt. loading. In order to improve compatibility and composite properties of PALF/poly(lactic acid) composites without any hazardous chemicals that are usually involved in the process, dielectric barrier discharge (DBD) plasma surface treatment was conducted for fiber modification. Therefore more environmentally friendlier and industrially scalable technology was implemented in processing of composites by twin screw extrusion and injection moulding. Resulted composites were characterized by means of scanning electron microscopy (SEM), thermal and mechanical testing. © 2016 Trans Tech Publications, Switzerland.
  • Thumbnail Image
    Item
    Einführung in die Kunststofftechnologien
    (2019-01-01) Běhálek, Luboš; Brdlík, Pavel; Borůvka, Martin; Lenfeldová, Irena
  • Thumbnail Image
    Item
    Hodnocení vlastností kompozitu s PP matricí a celulózovým plnivem
    (Technická Univerzita v Liberci, 2012-01-01) Borůvka, Martin; Lenfeld, Petr
    The aim of the thesis was evaluation of properties of composite with polypropylene matrix and cellulose filler. The evaluation was performed considering different percentage content and different size of filler. Further then according to the type of used additives. The theoretical part of the work deals with problems of composites reinforced by plant fibbers and their application.
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    Metody vyhodnocování typu porušení lepených spojů
    (2009-01-01) Borůvka, Martin
  • Thumbnail Image
    Item
    Metody vyhodnocování typu porušení lepených spojů
    (Technická Univerzita v Liberci, 2009-01-01) Borůvka, Martin; Doubek, Pavel
    The aim of the thesis was to compare the different evaluation methods of the mode of failure in adhesive bonds. The evaluation was performed by using eyesight, digital camera and scanning confocal laser microscope. The theoretical part of the work deals with problems of bonding in the automotive industry and with evaluation methods of the mode of failure in adhesive bonds in industrial practice.
  • Thumbnail Image
    Item
    Recycling of sisal fiber reinforced polypropylene and polylactic acid composites: Thermo-mechanical properties, morphology, and water absorption behavior
    (2019-01-01) Ngaowthong, Chakaphan; Borůvka, Martin; Běhálek, Luboš; Lenfeld, Petr; Švec, Martin; Dangtungee, Rapeephun; Siengchin, Suchart; Rangappa, Sanjay Mavinkere; Parameswaranpillai, Jyotishkumar
    The effect of recycling on the thermo-mechanical and water absorption behavior of polypropylene (PP)/sisal fiber and polylactic acid (PLA)/sisal fiber composites were studied. The PP-based non-biodegradable composites and PLA-based biodegradable composites were recycled for four times. The effect of recycling was determined by examining the morphology, thermo-mechanical properties, and water absorption behavior and the obtained results were compared. The results showed that the incorporation of sisal fibers in the PP and PLA matrix enhances the tensile modulus and percentage crystallinity of the composites. The tensile strength and modulus of the sisal fiber reinforced PP composites were not affected with recycling. Even though the tensile properties of PLA and PLA/sisal fiber reinforced composites are superior to PP and PP/sisal fiber composites, the PLA-based composites show a dramatic decrease in tensile strength and modulus after the first recycling due to the degradation of the polymer. The thermal stability of the PP/sisal fiber composites was not affected by the repeated recycling process. On the other hand, the PLA-based composites with higher sisal fiber content show a bit lower thermal stability after recycling. The PP-based composites show fluctuations in percentage crystallinity with recycling. On the other hand, a remarkable increase in percentage crystallinity for PLA and PLA-based composites was observed with increasing recycling times. Water diffusion study divulges that the diffusion of water into the polymer composites was reduced with recycling, irrespective of the polymer matrix.
  • Thumbnail Image
    Item
    Solid and microcellular polylactide nucleated with PLA stereocomplex and cellulose nanocrystals
    (SPRINGER, VAN GODEWIJCKSTRAAT 30, 3311 GZ DORDRECHT, NETHERLANDS, 2020-03-01) Borůvka, Martin; Běhálek, Luboš; Lenfeld, Petr; Brdlík, Pavel; Habr, Jiří; Wongmanee, Sorasak; Bobek, Jiří; Pechočiaková, Miroslava
    Blending polylactide (PLA) with poly(d-lactide) (PDLA) and cellulose nanocrystals (CNC)-based stereocomplex (SC) nanohybrids presents practical approach to produce fully biobased blends and nanocomposites with enhanced properties. This paper investigated the nucleation effect of PLA/PDLA and PLA/PDLA-g-MAH/CNC nanohybrids at low loading levels on the non-isothermal crystallization, morphology, as well as thermal and thermo-mechanical properties of PLA-based samples. Neat PLA, blends and nanocomposites were produced by conventional and microcellular injection molding. Nitrogen (N-2) in a supercritical state was used as the physical blowing agent for preparation of microcellular samples. CNC-based SC showed superior nucleating efficiency compared to SC nucleating agents. However, low mold temperature resulted in relatively low degree of crystallinity (similar to 15%). In addition, decrease in cell size and increase in cell density of microcellular samples have been observed after introduction of both nucleating agents. Slight increase in mechanical properties of nucleated samples compared to neat PLA has been ascribed to the higher degree of crystallinity. Despite these, decrease in all mechanical properties of microcellular samples has been noticed when compared to solid counterparts. Furthermore, dynamic mechanical analysis (DMA) reveals subsequent foaming and dramatic decrease in dimensional stability of microcellular samples above glass transition temperature (T-g). The storage modulus in a glassy region has been improved in both solid blends and nanocomposites. In addition, shift of T-g due to restricted chain mobility of PLA due to retarded relaxation of amorphous regions due to SC interactions has been observed.
  • Thumbnail Image
    Item
    Thermal degradation of the thermoplastic Elastomers during the injection Moulding process
    (Trans Tech Publications Ltd, 2016-01-01) Běhálek, Luboš; Habr, Jiří; Seidl, Martin; Lenfeld, Petr; Borůvka, Martin
    The thermal degradation of the thermoplastic elastomers (TPEs) during the injection moulding process – depending on the melt temperature and residence time of the processed material within the barrel of the injection unit, was studied on the basis of oxidation induction time evaluation (isothermal OIT) of the moulded parts (according to ISO 11357-6) and their physical and mechanical properties, according to ISO 1183-1, ISO 37 and ISO 7619-1. TPEs with different chemical compositions intended for automotive, industrial and medical applications were analysed during the study of the thermal degradation process. © 2016 Trans Tech Publications, Switzerland.
  • Thumbnail Image
    Item
    Thermal properties and non-isothermal crystallization kinetics of biocomposites based on poly(lactic acid), rice husks and cellulose fibres
    (SPRINGER, VAN GODEWIJCKSTRAAT 30, 3311 GZ DORDRECHT, NETHERLANDS, 2020-06-01) Běhálek, Luboš; Borůvka, Martin; Brdlík, Pavel; Habr, Jiří; Lenfeld, Petr; Kroisová, Dora; Veselka, Filip; Novák, Jan
    Bioplastics reinforced by agricultural waste fibres show promise to provide degradation back into the environment when they are no longer needed. These biocomposites have the potential to replace synthetic polymers from non-renewable resources in some applications and may turn out to be one of the material revolutions of this century. Unlike synthetic composites, biocomposites are renewable, carbon neutral, biodegradable and non-petroleum based and have low environmental, human health and safety risks. In this paper, poly(lactic acid) (PLA)-based biocomposites filled with technical cellulose fibres (CeF) and rice husks (RHs) at 10-30 mass% loading were prepared by twin-screw extrusion and injection moulding to enhance stiffness of resulting biocomposites. Particular attention was given to the enhancement of adhesion between the polymer matrix and natural filler through the physical modification by ozone (O-3) and dielectric barrier discharge (DBD) plasma (p) surface treatments. Further than, compatibilizing agent based on PLA-g-MAH was produced and introduced into the PLA systems. The non-isothermal crystallization behaviour and thermal properties were investigated through differential scanning calorimetry (DSC) under various cooling rates (5, 10, 20 and 40 degrees C min(-1)). The addition of both fillers increased overall crystallization kinetics of resulted biocomposites, especially at high cooling rates. An increase in crystallinity degree from 2.4 (neat PLA) up to 51% has been observed for PLA/30CeF(O3)samples at 40 degrees C min(-1)cooling rate. An increase in crystallinity degree based on mass percentage of filler was noticed especially for PLA/RH. Mass percentage increase in CeF did not notice significant increase in PLA crystallinity. The influence of RH and CeF on transformation behaviours of PLA alpha MODIFIER LETTER PRIME-/alpha-polymorphs was observed. The elimination of imperfect alpha MODIFIER LETTER PRIME-crystals was observed with increasing amount of RH and CeF.
  • Thumbnail Image
    Item
    Úvod do technologií zpracování plastů
    (2019-01-01) Běhálek, Luboš; Brdlík, Pavel; Borůvka, Martin; Lenfeldová, Irena
  • Thumbnail Image
    Item
    Výzkum aplikačních možností bio-kompozitních materiálů plněných nanokrystaly celulózy
    (2018-10-30) Borůvka, Martin; Lenfeld Petr, prof. Dr. Ing. Skolitel : 55397
    Disertační práce se zabývá komplexním výzkumem přípravy, modifikace a zpracování bio-kompozitních systémů s využitím nanokrystalů celulózy (CNC). Jako primární matrice bio-kompozitů byl zvolen polylaktid (PLA), cenově dostupný biopolymer s dobrými mechanickými vlastnostmi, biokompatibilitou a biologickou rozložitelností, který je založený na přírodních a obnovitelných surovinách. Laboratorně byla provedena extrakce CNC s jejich následnou povrchovou modifikací a zpracováním nanokompozitů pomocí rozpouštědlových systémů. Dále byl výzkum zaměřen na technologické možnosti zvyšování dispergovatelnosti a distribuce sprejově vysušovaných aglomerátů CNC v PLA matrici pomocí tavných technologií. S cílem odstranit křehkost PLA matrice výzkum dále směřoval k aplikačnímu potenciálu synergického působení změkčovadel a CNC. Výzkum lehčených nanokompozitů na bázi mikrobuněčných struktur cílil na potenciální strukturní aplikace s využitím reaktivně modifikovaných nanohybridů na bázi PLA stereokomplexu a CNC. S cílem souběžně zvyšovat houževnatost a teplotní odolnost pak byly připraveny multifázové stereokomplexované PLA nanokompozity. Hodnocen byl především vliv přidaných aditiv na kinetiku krystalizace, morfologii a termo-mechanické vlastnosti připravených materiálových systémů.