Volume 35, Issue 8

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.

This article deals with the electrical conductivity of a composite of two polymers, one of which is a conducting polymer, whereas the second is a dielectric. The problem was formulated within the framework of electrical percolation, i.e., the percolation thresholds, which allow for a high electrical conductivity, is under investigation. For this purpose, a numerical model was developed, and its parameters were analyzed and discussed. Based on the determined thresholds, it was possible to evaluate the weight ratios of the conducting-dielectric polymers in a composite. The proposed approach allows for reducing the manufacturing cost of composite material with respect to conducting polymers with simultaneous retaining of high conductance properties of conducting polymers, as well as durability and flexibility of dielectrics.

A new compound was synthesized from 2-hydroxy-1,2,3-propanetricarboxylic acid (citric acid) and diethylene glycol (DEG). Compound, tris(hydroxydietylene)-2-hydroxypropane-1,2,3-tricarboxylate (THT) rated properties in terms of suitability for the rigid polyurethane-polyisocyanurate (PUR-PIR). Rated properties of THT eg., acid number, density, pH, solubility. The resulting product was characterized by hydroxyl number 405.2 mg KOH/g and viscosity 4879.7 mPa·s. Compound used to foams in amounts of from 0.1 equivalents to 0.5 equivalents instead of Rokopol RF551. The results of rigid foams showed that the amount of THT in the foam significantly affects the compressive strength of foams. Its amount does not affect the apparent density of foam, retention and thermal conductivity. The foams are characterized by small values of fragility.

Poly(lactic acid) (PLA)/polypropylene (PP) blends with different weight fractions were prepared by a novel vane extruder. The mechanical properties, morphology, crystallization behavior and thermal stability of the blends were investigated. The tensile strength, flexural strength and elongation at break decreased nonlinearly when the PP content was not more than 50 wt% and then increased with an increase in the PP content. The flexural modulus decreased with increasing PP weight fraction. The PLA/PP 90:10 blend exhibited the optimum impact strength. Scanning electron microscopy measurements revealed that the PLA/PP blends were immiscible. Phase separation occurred significantly at a blend ratio of 50:50. Regarding the PLA/PP 90:10 blend, the mean diameter of the disperse-phase PP particles was the smallest at 1.11 μm. Differential scanning calorimetry measurements showed that low content of PP enhanced the crystallization of PLA. The PLA component in the blends impeded the crystallization of PP when PP was used as the matrix. The thermogravimetric analysis measurement involved a two-step decomposition process of the blends. The thermal resistance of the blends was improved by compounding with PP. As compatibilizers, both the maleic anhydride-grafted PP and the ethylene/ n -butyl acrylate/glycidyl methacrylate terpolymer helped improve the mechanical properties, crystallization property and thermal resistance of the PLA/PP blends.

The morphology of extruded films based on blends of polyvinyl alcohol (PVA) and poly(3-hydroxybutyrate) (PHB) was studied for various compositions. The methods of differential scanning calorimetry (DSC) and X-ray analysis were used. The phase-sensitive characteristics of the composite films, diffusion and water vapor permeability were also investigated. Processes of binding of water and swelling cause the first areas; processes of a relaxation and transition of structure of composites to an equilibrium condition, the second. In addition, the tensile modulus and relative elongation-at-break were measured. Changes in the glass transition temperature (T g ) of the blends and constant melting points of the components show their partial compatibility in intercrystalline regions. At a content of PHB in the composite films equal to 20–30% wt., the mechanical characteristics and water diffusion coefficients are dramatically changed. This fact, along with the analysis of the X-ray diffractograms, indicates a phase inversion in the above narrow concentration interval. The complex pattern of the kinetic curves of water vapor permeability is likely to be related to additional crystallization, which is induced in the composite films in the presence of water.

The objective of this work was to find a possible engineering application for polypropylene (PP) by preparing fibers filled with nanoclay particles. Unfilled and nanoclay filled (0–5 wt%) PP fibers were continuously drawn and examined. The surface morphology and topographic studies of fibers were carried out using a scanning electron microscope (SEM). It was observed that unfilled PP fibers possess poor density distribution with the nonuniform diameter across the fiber length affecting structural integrity. However, PP fibers filled with ≥2 wt% nanoclay had shown improvement in structural integrity. The structure and morphology of fibers were examined by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis, and the result indicated good dispersion of nanolayers of clay in PP matrix with exfoliated nanocomposite structure up to 2 wt% nanoclay and above 2 wt% showing intercalated nanocomposite structure. Improved tensile, thermal and water barrier properties of nanoclay filled PP were also observed.

A novel sheath-core poly(ethylene terephthalate) (PET)/poly(ethylene-co-vinyl alcohol) (EVOH) composite fiber was designed and manufactured to improve the hydrophilicity of the PET fibers. The thermal stability of EVOH was first examined to determine the possible processing temperature. Second, the rheological characteristics of EVOH were measured to obtain the appropriate spinning parameters. Then, PET/EVOH composite fibers with various sheath-core ratios were manufactured and the effect of sheath-core ratio on the stable spinning process was investigated. Scanning electron microscopy (SEM) shows that the PET/EVOH fibers possess a round sheath-core cross-section and a smooth surface, indicating successful spinning. Finally, the mechanical properties and moisture absorption of the PET/ EVOH composite fibers were measured. For PET/EVOH composite fibers, the PET content contributes to the mechanical properties and the EVOH content contributes to the moisture absorption. For the PET/EVOH composite fibers with a sheath-core ratio of 50:50, the moisture regains at room conditions reach to 2.8% and the breaking strength is 2.53 cN/dtex. These good mechanical and moisture properties attract good application prospects.

The aim of this research is to investigate the effects of different thermoplastic starches and starch contents on the physico-mechanical and morphological properties of new polymeric-based composites from low density polyethylene (LDPE) and thermoplastic starches. Different compositions of thermoplastic starches (5–40 wt%) and LDPE were melt blended by extrusion and injection molding. The resultant materials were characterized with respect to the following parameters, i.e., melt flow index (MFI), mechanical properties (tensile, flexural, stiffness and impact strength) and water absorption. Scanning electron microscopy (SEM) was also used in this study for evaluating blend miscibility. MFI values of all blends decreased as the starch content increased, while the sago starch formulation showed a higher MFI value than others. The incorporation of fillers into LDPE matrix resulted in an increased in tensile modulus, flexural strength, flexural modulus and slightly decreased tensile strength and impact strength. However, sago starch filled composites exhibited better mechanical properties as compared to other starches. The SEM results revealed that the miscibility of such blends is dependent on the type of starch used. The water absorption increased with immersion time and the thermoplastic sago starch samples showed the lowest percentage of water absorption compared with other thermoplastic starches.

The aim of this study was to produce epoxy composites highly filled with waste bulk molding compounds (BMC). The used amount of filler ranged from 30 wt% to 60 wt%. The influence of BMC on the epoxy resin curing process was monitored with the differential scanning calorimetry (DSC) method. Fourier transform infrared (FTIR) spectroscopy was used to evaluate the chemical structure of composites. The mechanical and thermal properties were examined by means of dynamic mechanical thermal analysis (DMTA), the Charpy method and the Shore D test. The fracture surface morphology of composites was observed with scanning electron microscopy (SEM). The storage modulus G′ of the epoxy composites with BMC was higher than the reference epoxy sample and significantly dependent on filler content. All investigated materials showed similar values of hardness, but at the same time low values of impact strength. Therefore, obtained composites can be used as low cost coating materials.