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Five polypropylene (PP) homopolymers were selected and their molecular structure was thoroughly characterized to determine the effect of molecular architecture on their annealing behavior and on the ultimate stiffness achieved by heat treatment. Molecular mass and its distribution were characterized by rheological measurements, while chain regularity was determined by differential scanning calorimetry (DSC) using stepwise isothermal segregation technique (SIST). The samples were annealed in two different ways. Tensile bars were treated in an oven at 165 °C for increasing times to determine changes in stiffness. Various defects (microcracks and voids) developed during the annealing of tensile specimens that did not allow the reliable determination of modulus by direct measurement. On the other hand, the second approach, the annealing of small samples in a DSC cell clearly showed the changes occurring in crystalline structure and also the effect of nucleation and molecular architecture on them. The large molecular weight fraction used to facilitate nucleation hinders crystal perfection, whereas the presence of a heterogeneous nucleating agent increases overall crystallinity, but does not influence recrystallization during annealing. Melting traces were transformed into lamella thickness distributions from which average lamella thickness was derived. Lamella thickness and crystallinity, the independent variables of the model equation used for the calculation of modulus, were extrapolated to infinite annealing time to predict maximum stiffness. The value obtained, 3.5 GPa, is very far from the theoretically predicted 40 GPa of oriented crystals, which cannot be achieved under practical conditions. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3365–3373, 2013

Five ethylene-propylene random copolymers were nucleated with two soluble nucleating agents. Ethylene content changed between 1.7 and 5.3 wt %, while nucleating agent content was adjusted according to the solubility of the additive. It changed from 0 to 5000 ppm for the sorbitol (1,2,3-tridesoxy-4,6:5,7-bis-O-[(4-propylphenyl) methylene]-nonitol) and from 0 to 500 ppm for the trisamide compound (1,3,5-benzene-trisamide) used. Crystalline structure was analyzed in detail by various methods (DSC, XRD, and SEM). Mechanical properties were characterized by tensile and instrumented impact measurements. The results showed that most properties changed moderately upon nucleation, but impact resistance increased considerably. Spherulitic structure was not detected, but instead in the presence of the soluble nucleating agents used a microcrystalline structure formed. The large increase of impact resistance could not be related directly to changes in crystalline morphology. On the other hand, local rearrangement of morphology was detected by XRD and SEM analysis including an increase of lamella thickness, crystal orientation, and the formation of shish-kebab structures in the core of the injection molded specimens. A small increase in the γ-phase content of PP was also observed. These changes increased crack propagation energy considerably leading to the large improvement observed in impact resistance. Although the phenomenon could be related to ethylene content, differences in molecular weight also helped to explain the changes observed. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43823.

Oligomeric polycaprolactone (oPCL) was used for the modification of cellulose acetate by reactive processing in an internal mixer at 180°C, 50 rpm, 60 min reaction time, and 45 wt % caprolactone (CL) content. The product of the reaction was characterized by several analytical techniques and its mechanical properties were determined by dynamic mechanical thermal analysis and tensile testing. The synthesized oPCL contained small and large molecular weight components. The small molecular weight fraction plasticized cellulose acetate externally and helped fusion. Although composition and structure did not differ considerably from each other when CL monomer or polycaprolactone oligomer was used for modification, the grafting of a few long chains had considerable effect on some properties of the product. The large molecular weight chains attached to CA increased the viscosity of the melt considerably and resulted in larger deformability. oPCL homopolymer is not miscible with cellulose acetate and migrates to the surface of the polymer. Exuded polycaprolactone oligomers crystallize on the surface but can be removed very easily. More intense conditions may favor the grafting of long chains leading to polymers with advantageous properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Various blend ratios of high-density polyethylene (HDPE) and ultrahigh-molecular-weight polyethylene (UHMWPE) were prepared with the objective of determining their suitability as biomaterials. Although the presence of HDPE in the blends enabled melt processing, the presence of UHMWPE helped to improve the toughness of the resulting blends. The processability of the blends was investigated with the Brabender torque, which was used as an indication of the optimum blend conditions. The blends were characterized with differential scanning calorimetry. The mechanical tests performed on the blends included tensile, flexural, and impact tests. A 50:50 (w/w) blend yielded optimum properties in terms of the processability and mechanical properties. The tensile property of the 50:50 blend was intermediate between those of HDPE and UHMWPE, but the strain at break increased 200% in comparison with that of both neat resins. The energy at break of the 50:50 blend revealed an improvement in the toughness. The fracture mechanism was also investigated with scanning electron microscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 413–425, 2005

Three types of mineral fillers—talc, calcium carbonate (CaCO3), and kaolin (10 - 40 wt % filler load- ings)—were compounded with polypropylene (PP) with a twin-screw extruder. The composites were injection- molded, and the effects of the filler loading on the mechan- ical, flow, and thermal properties for the three different types of filled composites were investigated. The aim was to compare their properties and to deduce prospective filler combinations that would yield hybrid PP composites in following studies. The results showed that in most cases, the strength and stiffness of the talc-filled PP composites was significantly higher than those of the CaCO3- and kaolin- filled PP composites. However, CaCO3, being a nonreactive filler, increased the toughness of PP. The kaolin-filled PP composites also showed some improvement in terms of strength and stiffness, although the increases in these prop- erties were not as significant as those of the talc-filled PP composites. The effects of interfacial interactions between the fillers and PP on the mechanical properties were also evaluated with semiempirical equations. The nucleating ability of all three fillers was studied with differential scan- ning calorimetry, and the strongest nucleating agent of the three was talc, followed by CaCO3 and kaolin. © 2004 Wiley

Ensuing our recent studies on polyethylene stabilization,1,2 further multiple extrusion experiments were carried out with a high-density polyethylene (HDPE) polymer containing various amounts of a sterically hindered phenolic antioxidant. Discoloration, thermoxidative stability, and melt flow index (MFI) retention were measured by standard techniques; the functional group content of the polymer was determined by Fourier transform infrared (FTIR) spectroscopy, and rheological, as well as mechanical properties, were also measured. The results indicated that degradation and stabilization reactions take place according to two different mechanisms in the first and subsequent processing steps, respectively. Color development could be described well by the simple first-order overall reaction kinetics proposed earlier, and color change could be related to the stability of the polymer. The existence of general correlations among the properties proved that all chemical reactions are interrelated. The reactions of the stabilizer lead to color development, while those of the polymer to a modification of its molecular architecture, which determines the rheological and mechanical characteristics of the product. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1596–1605, 1999

Poly(lactic acid) (PLA) composites were prepared using six lignocellulosic fibers with widely varying particle characteristics. The composites were characterized by tensile testing, scanning electron (SEM), and polarization optical microscopy (POM). Micromechanical deformation processes during loading were followed by acoustic emission measurements. Interfacial adhesion was estimated by three independent methods. Contrary to most claims published in the literature, interfacial adhesion between PLA and natural fibers was found to be rather strong, a result confirmed by the quantitative estimation of adhesion strength, acoustic emission measurements, and SEM study. Strong interfacial adhesion results in weak dependence of the extent of reinforcement on the particle characteristics of the reinforcing fibers. Both acoustic emission measurements and microscopy indicated that the dominating micromechanical deformation process is the fracture of the fibers and close correlation was found between the initiation stress of fiber fracture, reinforcement, and the ultimate strength of the composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39902.

The thermal degradation of PVC was measured under dynamic and static conditions. The UV and IR spectra, as well as the molecular weight distribution of the PVC samples, taken after different time intervals were measured. It was established that during the dynamic PVC degradation, performed in a mixing chamber, two stages with different degradation rates can be distinguished both in extinction and torque vs. time curves. While oxygen does not, dissolved HCl does play an important role in the dynamic degradation: HCl steps into reaction with the formed polyenes and has a catalytic action. The chemical degradation, particularly the crosslinking, produces the changes in the rheological behavior of the material. Results were compared with those obtained under static conditions in argon, air, and HCl atmosphere.