S. S. Pesetskii

Tribological behavior of nanocomposites produced by the dispersion of nanofillers in polymer melts

Literature data and original research in the field of the technology and tribology of nanocomposites produced by the dispersion of nanofillers including organoclay, carbon nanomaterials, and metal-containing compounds in thermoplastics and elastomers melts are analyzed. The features of their structure and tribological behavior are discussed. The combination of traditional and nanodispersed fillers in polymer composites is shown to hold promise, and the fields of the application of nanodispersed nanocomposites are considered.

Itaconic acid grafting on LDPE blended in molten state

Grafting of itaconic acid on low density polyethylene in the molten state has been investigated. Static and dynamic mixers assembled on the Brabender plastograph have been used as a blender of reagents and as a chemical reactor. Shear rates were 50 and 100 s−1. Dicumyl peroxide; 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane; 2,2-di-(tert-butyl-peroxy)-5,5,6-trimethylbicyclo-[2,2,1]-heptane; 2,2-di(3-methyl-1-butyne-3-peroxy)-5,5,6-trimethylbicyclo[2,2,1]heptane; 2,5-dimethyl-2-hydroxy-5-tert-butylperoxy-3-hexyne were used as peroxide initiators of grafting.

Free-radical grafting of itaconic acid onto LDPE by reactive extrusion: I. Effect of initiator solubility

The effect of the peroxide initiator nature on the grafting of itaconic acid (IA) onto low-density polyethylene (LDPE) was investigated in the course of the reactive extrusion. It was shown that at other equal conditions, the solubility of the peroxide initiator in the molten polymer is most important in the IA grafting onto LDPE. The thermal stability of peroxide initiators is also important. At the synthesis conditions of preparing the grafted products by the reactive extrusion, peroxides, which decompose at temperatures far below the IA melting point (also in the feed zone of the extruder), can be used to initiate grafting reactions. It is very probable that radicals formed from peroxide decomposition interact first with LDPE macromolecules, while the formed macroradicals initiate IA grafting reactions. Peroxides, which are easily dissolved in LDPE, are recommended for initiating the efficient grafting reactions. The closer the thermodynamic affinity between the peroxide and the monomer, the less the efficiency of grafting. Higher transportation velocities of the reactive blend in the extruder-reactor intensify LDPE crosslinking, thus lowering the IA grafting efficiency.

Blends of thermoplastic polyurethanes and polyamide 12: Structure, molecular interactions, relaxation, and mechanical properties

Studies were done to understand the effects of polyamide 12 (PA 12) incorporation on microphase separation (microsegregation) in thermoplastic polyurethanes (TPU) based on oligoether (polytetramethylene oxide, molecular weight, 1000) and oligoester (polyethylene butylene glycol adipate, molecular weight, 2000), and relaxation transitions, compatibility, and molecular interaction energy in polymer blends. It was learned that the addition of PA 12 caused partial degradation of the domain structure in the oligoester-containing polyurethane, whereas interaction of hard blocks in the oligoether-containing polyurethane increased. Analyzing compatibility and interphase interactions in blends is possible in the frame of the quantum theory of relaxation processes. Also, interferences of the components on characteristic temperatures of relaxation transitions were studied. Partial compatibility was detected between PA 12 and the soft block of oligoether-based TPU over the whole range of components concentrations tested. For oligoester-based TPU, partial compatibility was observed only at low polyamide concentrations (up to 20 wt %). Effects of a polyurethane phase on PA 12 crystallization in the blends along with the pattern of concentration—mechanical properties dependencies are discussed.

Effect of nanodisperse carbon fillers and isocyanate chain extender on structure and properties of poly(ethylene terephthalate)

The effect of diisocyanate chain extender (CE) on the mechanical, rheological, and relaxation properties, as well as on molecular weight and crystallizability, of starting poly(ethylene terephthalate) (PET) and its composites containing carbon nanomaterials (CNM) such as carbon nanotubes (CNTs) and commercial carbon (CC) has been studied. The composites were compounded in molten PET using twin-screw extruder (screw diameter 35 mm; L/D = 40). To improve the distribution of CNM in the polymeric matrix (before introduction into the melt), they were blended with PET powder and subjected to an ultrasonic treatment in methylene chloride. The salient features of the materials structure were estimated based on DSC and relaxation spectrometry (dynamic mechanical analysis) data. It has been found that CNM additives partly suppress the PET-chain extension reactions which take place during interaction between macromolecular end groups and CE. Besides, both CNT and CC favour crystallizability of the modified PET owing to nucleation of the crystallization process. The influence of CNT appears to be more effective than that of CC. Enhancements in true mechanical strength and deformability of PET/CE/CNM composites, as against PET/CE materials, were found to be most clearly exhibited by the CNT-containing composites.

Chapter 5 – Tribological behavior of polymer nanocomposites produced by dispersion of nanofillers in molten thermoplastics

An analysis has been made of the literature on friction and wear of polymer nanocomposites prepared by compounding nanofillers with molten thermoplastics. A process is described for preparing the nanocomposites with various binders, for example, polar and nonpolar thermoplastics, aliphatic, aromatic, and partially aromatic polymers, as well as amorphous and partially crystalline polymers by reactive extrusion. The most important group of triboengineering nanocomposites includes thermoplastics containing the following fillers, carbon nanomaterials, layered clays, metals, and metal-containing compounds. The introduction of nanofillers into thermoplastics influences the kinetics and mechanism of tribochemical transformations in a friction contact with metals or other materials. Nanofillers significantly affect the physicochemical behavior of macromolecules, as well as the macromolecular transformations, at the conditions of frictional interaction. This can be explained by adsorption (chemisorption) of functional groups found on the particle surface, variations in polymer crystallinity and morphology, constrained molecular (segmental) mobility in macrochains, and catalytic (inhibiting) effects of the additives on the course of contact reactions. As a consequence, alterations occur in the formation of transfer layers and wear debris, along with the parameters of friction. Depending on the polymer, the nature and concentration of the fillers, the latter can either improve or impair the performance parameters of friction pairs.

Polymer Nanocomposites with Thermoplastic Matrices—Processing and Tribology

An analysis has been made of the literature on tribology of polymer nanocomposites prepared by compounding nanofillers with molten thermoplastics. A process is described for preparing nanocomposites with various polymer binders by reactive extrusion. The introduction of nanofillers (carbon nanomaterials, layered clays, metals, and metal-containing compounds) into thermoplastics influences the kinetics and mechanism of tribochemical transformations in a friction contact with metals or other materials. Nanofillers affect significantly the physicochemical behavior of macromolecules, as well as the macromolecular transformations, under the conditions of frictional interaction. This can be explained by adsorption (chemisorption) of functional groups found on the particle surface, variations in polymer crystallinity and morphology, constrained molecular (segmental) mobility in macrochains, and catalytic (inhibiting) effects of the additives on the course of contact reactions. As a consequence, alterations occur in the formation of transfer layers and wear debris, along with the parameters of friction. Depending on the polymer and the nature and concentration of the fillers, the latter can either improve or impair the performance parameters of friction pairs.

Functionalization of polyolefin melts containing carbon nanotubes and the properties of their blends with polyamide 6

Abstract The effect of multiwalled carbon nanotubes (MWNT) on the course of reactive-extrusion-free-radical grafting of trans-ethylene-1, 2-dicarboxylic acid onto linear low-density polyethylene (LLDPE) and ethylene-propylene copolymer (c-PP) containing ≈7 wt.% ethylene units was studied. The extrusion reactor was the material cylinder of the twin-screw extruder TSSK-35/40 (screw diameter 35 mm; length/diameter ratio=40; 10 independent heating zones). It was found that the extent of the influence of MWNT depends on their concentration and on the PO character. It is shown that monomer grafting efficiency can be improved with a MWNT concentration of ≈0.05 wt% in the reactive system. In free-radical grafting of the cross-linkable LLDPE, the MWNT (≥0.1 wt%) were shown to inhibit the concurrent process of macromolecular cross-linking; in the case of c-PP, which predominantly undergoes degradation during functionalization, the concurrent reactions were observed to accelerate catalytically. In the case of polyamide 6/LLDPE blends, the MWNT promote the strengthening of melt flow junctures that formed during the filling of the die-mold cavity.

Thermomechanical spectrometry of friction products formed in friction of compatibilized PA-6/HDPE blend with steel

Friction products (surface layers of the polymer sample, wear products, layers of polymer material transfer to the metal counterface) from the friction on steel of PA-6/HDPE blend, compatibilized HDPE with grafted methylene-butane-dione acid with the composition PA-6/(HDPE/HDPE-gr-MA-25 mass %)-20 mass % *, are studied using thermomechanical spectrometry. A considerable influence of contact load on the molecular- topological structure of these products is revealed. It is established that component redistribution takes place in the friction products, and this redistribution changes their ratio in the blend and their molecular-topological structure; in this case, none of the wear products has the structure of any of the components of the blend for the studied contact load range (1–6 MPa). It is shown that one of the following mechano-chemical processes, depending on the contact load, takes precedence in the polymer material during friction on steel: macromolecule destruction accompanied by decrease in their molecular mass, increase in molecular mass due to formation of linked and presumably copolymer structures, decrease or increase in crystallinity, and change of relaxation properties.