Ferenc Tuba

Mechanical and rheological response of polypropylene/boehmite nanocomposites

In this study, the influence of synthetic boehmite alumina nanoparticles with various surface treatments on the morphology, crystallization behavior and mechanical properties of polypropylene copolymer nanocomposites was studied. In particular, a series of polypropylene/boehmite alumina nanocomposites, containing up to 10 wt% of untreated and of octylsilane-functionalized boehmite alumina nanoparticles, were prepared by melt compounding and film blowing. A third type of composite was produced by incorporation of boehmite alumina nanoparticles treated with benzene sulfonic acid. Scanning electron microscopy indicated that boehmite alumina nanoparticles were finely and uniformly dispersed, though agglomerated, in the polypropylene nanocomposites. Surface-treated boehmite alumina nanoparticles were better dispersed in the matrix than the untreated boehmite alumina nanocomposites. The melt viscosity of nanocomposites remained unaltered or decreased by nanofiller incorporation at low concentration (2.5 and 5 wt%), while it slightly increased at higher concentrations (10 wt%). Uniaxial tensile tests indicated that the nanoparticles can induce a remarkable stiffening effect even at a rather low filler content, especially in the case of surface-treated particles. The plane stress fracture toughness of the material, evaluated by the essential work of fracture approach, showed a noticeable improvement due to boehmite alumina incorporation, with an optimal effect for a filler concentration of about 2.5 wt%.

The role of ultimate elongation in the determination of valid ligament range of essential work of fracture tests

In this study, the feasibility of a previously proposed ultimate elongation-based criterion of essential work of fracture (EWF) method was reconsidered for several materials. Suitable ductility level (DL) ranges for the EWF testing of polymers were discussed, too. It was shown that there is a relationship between the DL terms and the experimentally estimated crack opening displacement values. Based on Coterell’s estimate of the size of the fracture process zone a lower ligament limit of EWF concept was also presented. This lower bound should be considered for thin samples where the original thickness-dependent criteria seemed to be not severe enough.

Investigation of Time-Dependent Behavior of Starch-Based, Injection Molded Biodegradable Polymer

Nowadays as a result of the increasing environmental friendly consciousness and the decreasing oil reserves, natural origin based materials are developed. These materials are not only based on renewable, natural resources, but capable of biodegradation in compost. These biodegradable polymers (biopolymers) can be inserted into the nature’s recycling process. One of the most important biopolymers is starch. Starch can be processed like a thermoplastic material by adding plasticizers, creating the so called thermoplastic starch. However the price of starch is rather low, it has certain drawbacks retarding its wide industrial usage. It is sensitive to moisture, disrupts in pure water, has low mechanical properties, and in time it ages. This ageing or time-dependent behavior was analyzed with injection molded tensile specimens. The shrinkage and mechanical properties of the specimens were determined as a function of ageing time. The fracture surface was analyzed by scanning electron microscope. The results of the measurements were compared with previous examinations.

Rapid Tooling Technologies in the Processing of Thermoplastic Polymers

Thousands of people are affected by the newest achievements of material science and manufacturing technologies each year in the form of biomedical implants. In this field, the aim of developement is to create individual implants to satisfy the geometrical and adapting requirements of the patient. This manufacturing process has been recently improved by shortening the cycle time and using cost effective methods. Biocompatible thermoplastic polymers can be shaped with hot pressing technique. Rapid Tooling was used to create a forming tool for manufacturing process. 3D Printing was used to fabricate the computer generated forming tool. This tool was reinforced by infiltrating it with an epoxy resin. Different epoxy resins were examined to secure the best mechanical properties of this tool. Then the reinforced tool was used for hot pressing of the biocompatible thermoplastic polymer, poly(ε-caprolactone).