CHAIN REGULARITY OF ISOTACTIC POLYPROPYLENE DETERMINED BY DIFFERENT THERMAL FRACTIONATION METHODS

Abstract The chain regularity of isotactic polypropylene (iPP) homo- and random copolymers was characterized by different thermal fractionation methods in this study. Different stepwise temperature programs were applied in a calorimeter (DSC), in order to develop a method which is significantly faster than SIST and provides reliable information about the chain regularity of iPP. Our studies prove that self-seeding accelerates the crystallization process during annealing in SSA-DSC experiments (successive self-nucleation and annealing). Consequently, the time of isothermal steps can be shortened significantly in the SSA-DSC method. On the other hand we found that step time should not be too short if the goal of the measurement is the determination of average chain regularity. Our results clearly indicate that both the experimental conditions and the evaluation technique influence the obtained results. A standard experimental procedure is proposed for reliably determining the average chain regularity of iPP. The length of the SSA-DSC temperature program developed in this study is much shorter compared to that of the conventional SIST (stepwise isothermal segregation technique) measurements used recently for such experiments. The proposed SSA-DSC program makes the reliable characterization of a large number of samples on an acceptable timescale possible

The role of solubility and critical temperatures for the efficiency of sorbitol clarifiers in polypropylene

The optical properties of polypropylene (PP) were modified by nine different sorbitol type clarifiers available commercially or synthesized in the study. The solubility of the clarifiers in PP was estimated by thermodynamic model calculations. The results showed that the solubility of these additives in PP is small, a few 1000 ppm at most. Solubility is determined by the chemical structure of the sorbitol and the heat of fusion of the latter changes solubility by at least one order of magnitude. Solubility can be estimated reasonably by the Flory-Huggins lattice theory. The morphology of most sorbitols transforms at a temperature much below their melting point upon heating. This transformation, which is accompanied by crystal perfection, seems to influence melting and solubility. A fibrillar structure forms upon the cooling of molten sorbitols, but the diameter of the fibrils is much larger than those forming in the polymer melt. The nucleating effect of the clarifier depends on solubility, but also on processing conditions. Nucleus density is related to the amount of dissolved clarifier. A close correlation was found between the Flory-Huggins interaction parameter of sorbitols and the minimum achievable haze, which can be explained with the effect of solubility and nucleus density

Improvement of the impact strength of ethylene-propylene random copolymers by nucleation

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

Fracture resistance of hybrid PP/elastomer/wood composites

PP was modified with elastomer and wood to prepare materials with large stiffness and impact resistance. Three wood fibers with different particle characteristics were used, and elastomer as well as wood content changed in a wide range. Interfacial adhesion was modified through the use of maelated polypropylene (MAPP) coupling agent. The structure of ternary PP/elastomer/wood composites was manipulated by the use of functionalized polymers and processing conditions. Considerable embedding of the wood into the elastomer was achieved in some cases depending on the variables. Wood increases impact resistance slightly, elastomer drastically in two-component composites and blends, but fracture toughness remains small in three-component hybrid systems irrespectively of structure. Depending on particle size and interfacial adhesion fiber fracture and debonding occur in wood reinforced composites, mainly plastic deformation takes place in blends. This latter process is suppressed by cavitation promoted further by the presence of wood fibers which increase local stresses. The usual concept of three-component materials does not work in wood composites, micromechanical deformations must be controlled to diminish or completely eliminate cavitation and to increase the plastic deformation of the matrix polymer

Effect of the molecular structure of the polymer and nucleation on the optical properties of polypropylene homo- and copolymers.

Two soluble nucleating agents were used to modify the optical properties of nine PP homo- and random copolymers. The ethylene content of the polymers changed between 0 and 5.3 wt%. Chain regularity was characterized by the stepwise isothermal segregation technique (SIST), while optical properties by the measurement of the haze of injection molded samples. Crystallization and melting characteristics were determined by differential scanning calorimetry (DSC). The analysis of the results proved that lamella thickness and change in crystallinity influence haze only slightly. A model was introduced which describes quantitatively the dependence of nucleation efficiency and haze on the concentration of the nucleating agent. The model assumes that the same factors influence the peak temperature of crystallization and optical properties. The analysis of the results proved that the assumption is valid under the same crystallization conditions. The parameters of the model depend on the molecular architecture of the polymer. Chain regularity determines supermolecular structure and thus the dependence of optical properties on nucleation

Scientific research complex for the study of human operator in extreme conditions

In paper is presented a research complex which will recreate as closely as possible the diversity of the real working environment with appropriate incentives and will register the necessary examination of physical, physiological signals and parameters. Apparatus complex will simulate close to real work situations, will include tests necessary to assess the psychological status of the research subject. Further ahead in the complex algorithm will monitor the overall conduct of the experiment will record and process information from all physiological channels: electro miograma, electrocardiogram, blood pressure, pulse wave, respiration rate, galvanic skin response. The operator will receive visual and auditory information from the computer complex and will communicate with him through a special keyboard, standard optical mouse, track ball, stick and pedal controls. It is proposed methodology for conducting comprehensive studies of operator in extreme conditions. The developed complex will contribute to enhancing the skills of operators of mission-critical systems - pilots, pilots, operators of unmanned aerial vehicles, astronauts, heads of air traffic, nuclear operators and drivers of public transport