Anton Popelka

Polysaccharides Coatings on Medical-Grade PVC: A Probe into Surface Characteristics and the Extent of Bacterial Adhesion

Medical-grade polyvinyl chloride was coated by polysaccharides through a novel physicochemical approach. An initial surface activation was performed foremost via diffuse coplanar surface barrier discharge plasma in air at ambient temperature and pressure. Then, radical graft copolymerization of acrylic acid through grafting-from pathway was directed to render a well-defined brush of high density, and finally a chitosan monolayer and chitosan/pectin alternating multilayer were bound onto the functionalized surfaces. Surface characteristics were systematically investigated using several probe techniques. In vitro bacterial adhesion and biofilm formation assays indicated that a single chitosan layer was incapable of hindering the adhesion of a Staphylococcus aureus bacterial strain, while up to 30% reduction was achieved by the chitosan/pectin layered assembly. On the other hand, chitosan and chitosan/pectin multilayer could retard Escherichia coli adhesion by 50% and 20%, respectively. Furthermore, plasma treated and graft copolymerized samples were also found effective to diminish the degree of adherence of Escherichia coli.

Polyolefin in Packaging and Food Industry

The commonly used food packaging polymers are polyolefins, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), isotactic polypropylene (PP), and some polyethylene-based copolymers.

2D Ti3C2Tx (MXene)-reinforced polyvinyl alcohol (PVA) nanofibers with enhanced mechanical and electrical properties

Novel 2D Ti3C2Tx (MXene)-reinforced polyvinyl alcohol (PVA) nanofibers have been successfully fabricated by an electrospinning technique. The high aspect ratio, hydrophilic surfaces, and metallic conductivity of delaminated MXene nanosheet render it promising nanofiller for high performance nanocomposites. Cellulose nanocrystals (CNC) were used to improve the mechanical properties of the nanofibers. The obtained electrospun nanofibers had diameter from 174 to 194 nm depending on ratio between PVA, CNC and MXene. Dynamic mechanical analysis demonstrated an increase in the elastic modulus from 392 MPa for neat PVA fibers to 855 MPa for fibers containing CNC and MXene at 25°C. Moreover, PVA nanofibers containing 0.14 wt. % Ti3C2Tx exhibited dc conductivity of 0.8 mS/cm conductivity which is superior compared to similar composites prepared using methods other than electrospinning. Improved mechanical and electrical characteristics of the Ti3C2Tx /CNC/PVA composites make them viable materials for high performance energy applications.

Polyolefin Adhesion Modifications

Polyolefins exhibit excellent properties and the knowledge of their adhesion that are very important for many applications such as those in packaging, building, automobile, aeronautic, aerospace, electronics, and sport industries. Poor surface adhesion represents a serious problem in situations where other laminates, films, or metallic layers are imparted onto polyolefins. Adhesion represents the contact between two solids, for instance, in coatings, polymer blends, paints, multilayered sandwiches, adhesive joints, or composites materials.

Study of Adhesion and Surface Properties of Modified Polypropylene

Isotactic polypropylene (iPP) is one of the most frequently applied polymers. Unfortunately, it has a disadvantage of being non-polar which makes the adhesive joints formed with other, more polar polymers, rather week (Brewis & Mathieson, 2002; Chodak & Novak, 1999; Pocius, 1997; Kinloch, 1987; Schultz & Nardin, 1994; Kolluri, 1994; Denes & Manolache, 2004). From the point of view of application of iPP it is desirable that their adhesive properties are improved (Yalizis et al.,2000; Ohare et al., 2002; Shenton et al., 2001; Kim et al., 2002; Moosheimer & Bichler, 1999). This demand can be met by a modification of iPP, while polymer can be modified either at the surface directly, e.g. by plasma of electric discharge (Denes & Manolache, 2004), or in bulk, by addition of a suitable polar lowor high-molecular compound to the polymeric matrix (Novak & Florian, 1994; Novak et al., 2004; Novak & Florian, 2001; Novak, 1996). The presented contribution aims at offering the efficient methods of surface modification of iPP, from the point of view of improving its adhesion properties. Recent achievements will be discussed to evaluate physical and chemical changes taking place as a result of modification.

Piezoresponse, Mechanical, and Electrical Characteristics of Synthetic Spider Silk Nanofibers

This work presents electrospun nanofibers from synthetic spider silk protein, and their application as both a mechanical vibration and humidity sensor. Spider silk solution was synthesized from minor ampullate silk protein (MaSp) and then electrospun into nanofibers with a mean diameter of less than 100 nm. Then, mechanical vibrations were detected through piezoelectric characteristics analysis using a piezo force microscope and a dynamic mechanical analyzer with a voltage probe. The piezoelectric coefficient (d33) was determined to be 3.62 pC/N. During humidity sensing, both mechanical and electric resistance properties of spider silk nanofibers were evaluated at varying high-level humidity, beyond a relative humidity of 70%. The mechanical characterizations of the nanofibers show promising results, with Young’s modulus and maximum strain of up to 4.32 MPa and 40.90%, respectively. One more interesting feature is the electric resistivity of the spider silk nanofibers, which were observed to be decaying with humidity over time, showing a cyclic effect in both the absence and presence of humidity due to the cyclic shrinkage/expansion of the protein chains. The synthesized nanocomposite can be useful for further biomedical applications, such as nerve cell regrowth and drug delivery.

Acrylic Acid Plasma Treatment of Polypropylene Nonwoven Fabric

Nowadays hydrogel materials are being used in medical practice for wound dressing purposes. Hydrogel/textile composites can be formed to increase the mechanical strength and handling capability of hydrogel materials. Nonwoven textiles are optional for such applications, however, it is often necessary to improve their surface properties. Here plasma activation/ grafting of polypropylene (PP) nonwoven fabric with an acrylate layer to improve its adhesive properties is reported. A diaphragm discharge was used for the plasma treatment of the PP fabric. The discharge was burnt in a solution of acrylic acid (AAc), which resulted in a single step process of plasma activation and plasma grafting of the fabric. Results of wettability testing and ATR-FTIR measurements showed the existence of a thin poly(acrylic acid) (PAAc) layer grafted on the fabric surface. Peel strength measurements showed a 4.7 fold increase in the peel strength when compared with untreated PP fabric.

Highly transparent low sheet resistance electrodes for solar cell applications

High aspect ratio copper nanowires were synthesized, using a solution-based approach. The nanowires along with reduced graphene oxide thin films were sprayed onto glass and flexible substrates and later annealed in order to produce transparent conducting electrodes (TCEs). These electrodes exhibited 91.5% optical transmissivity and around 9- Ω/sq sheet resistance, which are comparable to Indium Tin Oxide (ITO). In addition, the hybrid TCEs, when exposed to ambient temperature showed slowed sheet resistance degradation. The electrodes deposited on a flexible substrate, showed immunity against any notable changes in the sheet resistance, when gone through numerous bending cycles. Adaption of such nanomaterials in conducting films could lead to the potential alternatives for the conventional ITO, with applications in numerous industries, including solar cells manufacturing.