Force oscillation occurring during the tensile testing of poly(ethylene terephthalate) (PET), resulting in periodical cavitation of the test specimens, has been studied. A mathematical model has been developed to describe the phenomenon, wherein special fibre bundles are assigned to the amorphous molecular chains. In order to model the local periodical transformations and the rate dependent viscoelastic behaviour the coupled fibre bundle cells were supplemented with a twoelement Maxwell model. Using the parameters determined from the measurements the model was compared to the measured force-elongation diagrams and it has been concluded that the simple model can be well used to describe the phenomenon.
Fluorinated surface groups were introduced into poly(dimethylsiloxane) (PDMS) coatings by plasma treatment using a low pressure radio frequency discharge operated with tetrafluoromethane. Substrates were placed in a remote position downstream the discharge. Discharge power and treatment time were tuned to alter the chemical composition of the plasma treated PDMS surface. The physicochemical properties and stability of the fluorine containing PDMS were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and contact angle measurements. Smooth PDMS coatings with a fluorine content up to 47% were attainable. The CF4 plasma treatment generated a harder, non-brittle layer at the top-most surface of the PDMS. No changes of surface morphology were observed upon one week incubation in aqueous media. Surprisingly, the PDMS surface was more hydrophilic after the introduction of fluorine. This may be explained by an increased exposure of oxygen containing moieties towards the surface upon re-orientation of fluorinated groups towards the bulk, and/or be a consequence of oxidation effects associated with the plasma treatment. Experiments with strains of marine bacteria with different surface energies, Cobetia marina and Marinobacter hydrocarbonoclasticus, showed a significant decrease of bacteria attachment upon fluorination of the PDMS surface. Altogether, the CF4 plasma treatments successfully introduced fluorinated groups into the PDMS, being a robust and versatile surface modification technology that may find application where a minimization of bacterial adhesion is required.
The theoretical and experimental study of a thermoplastic polymer foaming process is presented. Industrial scraps of PET were used for the production of foamed sheets. The process was performed by making use of a chemical blowing agent (CBA) in the extrusion process. Due to the low intrinsic viscosity of the recycled PET, a chain extender was also used in order to increase the molecular weight of the polymer matrix. Pyromellitic dianhydride (PMDA) and Hydrocerol CT 534 were chosen as chain extender and CBA, respectively. The reactive extrusion and foaming were performed in a two step process. Rheological characterization was carried out on PET samples previously treated with PMDA, as well as the morphological study was performed to define the cellular structure of the foams produced. Moreover, in order to predict the morphology of the foam, a non isothermal model was developed by taking into account both mass transfer phenomenon and viscous forces effect. Model results were compared with experimental data obtained analyzing the foamed samples. The model was validated in relation to working conditions, chemical blowing agent percentage and initial rheological properties of recycled polymer. A pretty good agreement between experimental and calculated data was achieved.
In this investigation, a novel temperature-pH responsive copolymer was prepared by the radical copolymerization between 2-hydroxypropyl acrylate (HPA) and aminoethyl methacrylate hydrochloric salt (AMHS). The molecular structure of the corresponding copolymer has been confirmed by 1H NMR and FTIR measurements. The results indicated that the lower critical solution temperature (LCST) of the resulting copolymer has shown a considerable dependence on the monomer ratio and pH value in the medium. When the molar ratio of HPA to AMHS unit on polymer chain was fixed at 1.56, 2.25, and 3.01, the LCSTs of copolymers were observed at 36.5, 28.2 and 17.8°C, respectively. For the effect of additive salts, the LCST change of the copolymer was affected by both cations and anions in the following order of Al(NO3)3 > KNO3 > Mg(NO3)2 > NaNO3 and KCl ≈KSCN > KBr > KNO3 > KI. The copolymer seems to be useful as a candidate for the controlled-drug release carrier by pH and temperature external stimuli.
Silane method is a preferred method in crosslinking polyethylene to modify its properties. Here, the silane grafting reactions of low density (LDPE), linear low density (LLDPE) and high density polyethylene (HDPE) were compared, all with a fixed amount of silane (vinyltrimethoxysilane) and peroxide (dicumylperoxide). Processing for silane grafting was carried out in an internal mixer, and FTIR spectra were used for comparing the silane grafting efficiencies. The effect of polymer physical form and pre-mixing the components was also determined. Molecular structure parameters were analyzed to investigate their effect on silane grafting efficiency. In case of LDPE and LLDPE, the probable interfering effect of two types of antioxidants on silane grafting reactions was studied. Ethylene propylene diene monomer (EPDM) was added to LDPE to evaluate its effect on silane grafting efficiency. Amongst different grades of polyethylene, LLDPE had a better efficiency in silane grafting. Branchings, PDI, Mw, and MFI are all determining factors and should be considered in comparing the silane grafting efficiency between different grades of polyethylene. In case of incorporating antioxidant, different results were observed when the polymer under study was different. EPDM as an additive would enhance silane grafting efficiency.
Polypropylene (PP) and PP/organo-montmorillonite (OMMT) compounds containing antistatic agent (3, 6 and 9 wt%) were prepared using co-rotating twin screw extruder followed by injection molding. PP/OMMT composites were prepared by mixing of PP, OMMT and maleated PP (PPgMAH). The mechanical properties of PP blends and PP/OMMT nanocomposites were studied by tensile and impact tests. The effect of antistatic agent (AA) on the surface resistivity of PP and PP/OMMT nanocomposites were studied. The morphological properties of PP blends and PP/OMMT nanocomposites were characterized by using field emission scanning electron microscopy (FESEM). The intercalation of OMMT silicates layer in PP nanocomposites was characterized using X-ray diffraction (XRD). The impact strength of PP blends and PP/OMMT nanocomposites did not vary significantly by the addition of antistatic agent. The tensile modulus and tensile strength of PP/OMMT nanocomposites were slightly decreased with the increasing loading of antistatic agents. From FESEM analysis, the dispersion of antistatic agent in the PP matrix can be revealed. In addition, the surface resistivity of PP/OMMT compound was affected by the loading of antistatic agent. XRD results indicated the formation of intercalated nanocomposites for PP/OMMT/AA.
Peroxide cured hydrogenated acrylonitrile/butadiene rubber (HNBR) compounds with 20 parts per hundred rubber (phr) active fillers, such as carbon black (CB), multiwall carbon nanotube (MWCNT) and silica were produced and their friction and wear properties under unlubricated rolling and sliding conditions were evaluated. The network-related properties of the HNBR compounds were deduced from dynamic-mechanical thermal analysis (DMTA). The coefficient of friction (COF) and the specific wear rate (Ws) were determined in different home-made test rigs. The CB and MWCNT containing HNBR compounds exhibited the best resistance to rolling and sliding wear, respectively, among the HNBR systems studied. The worn surfaces were inspected in scanning electron microscope (SEM) and the wear mechanisms were analyzed and discussed in respect to the types of wear and fillers.