Polymers are used for modification of the cement-based composites and others building materials since the thirties of 20th century. Based on the conclusions of recent studies, it is assumed that even water soluble polymers could be used as an admixture for such modification. Currently, there exist and are exploited several possibilities for polymer modification of mortars, wood-based products or bituminous asphalts. Various options differ in the way of modification, which can be basically applied to the entire volume or just a surface, but also in the form of the polymer used – either in the form of solution or fibers. The aim of our study was to investigate the influence of volume modification by the water soluble polymers, such as polyvinyl alcohol (PVA), on the properties of cement paste and find an optimum additive. It turned out that the addition of PVA solution into fresh cement paste results in an increase of porosity and therefore a stiffness and compressive strength reduction. On the other hand, the bending strength of PVA-rich specimens was significantly higher and their water absorption decreased, which may consequently result in enhanced frost resistance.
Abstract. Knowledge about the microstructure and the morphology of individual phases within wood tissues is essential for numerous applications in materials engineering and in the construction industry. The purpose of the work presented here is to monitor the distribution of elastic stiffness within the tissues of individual cells using state-of-art equipment and exploiting emerging methods, such as modulus mapping, to investigate the morphology of the individual phases. Quasi-static nanoindentation was carried out on cell walls of spruce earlywood and latewood tracheids to obtain values for the indentation modulus, which is closely related to the Young modulus of the material. Dynamic modulus mapping, also known as nanoDMA, was utilized to obtain a map of the elastic moduli over the entire tracheid cross-section. In particular, it was found that the indentation stiffness of the cells walls ranges between 10.5 GPa for of earlywood tracheids and 12.5 GPa for latewood tracheids. The difference between the elastic stiffness of earlywood and latewood is attributed to the different chemical composition and the orientation of the fibrils. The data that has been acquired is indispensable for micromechanical modeling and for the design of engineered products with superior mechanical properties.
Abstract. The unique properties of nanotextiles based on poly(vinyl-alcohol) (PVA) manufactured using the electrospinning method have been known and exploited for many years. Recently, the enrichment of nanofiber textiles with nanoparticles, such as ions or nanodiamond particles (NDP), has become a popular way to modify the textile mechanical, chemical and physical properties of the textile. The aim of our study is to investigate the macromechanical properties of PVA nanotextiles enriched with NDP, silver (Ag) and copper (Cu) ions. Nanofiber textiles of various surface weights were prepared from a 16 % PVA solution, while glyoxal and phosphoric acid were used as cross-linking agents. The copper and silver ions were diluted in an aqueous solution and NDP were dispersed into the fibers by ultrasound homogenization. All but one of the sets of samples were exposed to a temperature of 140°C for 10 minutes. The samples without thermal stabilization exhibited significantly lower elastic stiffness and tensile strength. Moreover, the results of tensile testing indicate that the addition of dispersed nanoparticles has a minor effect on the mechanical properties of the textiles and contributes rather to their reinforcement. However, the lack of thermal stabilization results in a poor interconnection of individual nanofiber layers, and the non-stabilized textiles exhibit lower elastic stiffness and reduced tensile strength.
This paper discusses characterization of physical and mechanical properties of tissues of Norway spruce. Cell wall is composed of several layers, which is, due to their small size, difficult to characterize. For this reason, the work uses a combination of methods, atomic force microscopy (AFM) and nanoindentation. AFM is used to determine the topography of samples and nanoindentation to determine micromechanical properties of wood tissues. Prepared samples of glue laminated timber were tested by quasi-static and dynamic nanoindentation (modulus mapping technique) method.
Nanofiber textiles became indispensible in medicine and many other industries because of their unique properties. Recently, the pioneering works suggested their use also in a building industry in the form of moisture barriers. For a better chemical stability and resistance to air humidity it is suitable to stabilize the spun textiles. Our study is focused on the influence of the physical-chemical stabilization, also called crosslinking, on the mechanical properties of nanofiber textiles in tension, namely stiffness, strength and ductility. During the process of crosslinking the individual fibers bond in nodes, ensuring a better spatial integrity. However, the presented results indicate that the stabilized nanofiber textiles exhibit significantly lower ductility while their ultimate strength is lower only by about 10 %.
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