Iranian Polymer Journal
Year:2007 | Volume:16 | Issue:2 (80)|Papers Count:7

Some bimodal molecular weight distributed polystyrene samples were produced through blending the products of the free radical polymerization processes of the two parallel reactors. The two types of prepared low molecular weight polystyrenes (Mn = 40000 and Mn = 79000) at 5, 10, 15, and 20 %wt were blended with high molecular weight polystyrene (Mn = 211000), respectively. The physical and mechanical properties of these polymer blends were investigated by measuring the amount and molecular weight effects of the low molecular weight fractions on the final molecular weight distribution (MWD) and melt flow index (MFI) of the polystyrene blended samples. The results showed that the final MWD and MFI were significantly affected by the number average molecular weight and weight ratio of the low molecular weight fractions in the polystyrene blends. Furthermore, dynamic mechanical analysis (DMA) properties were determined experimentally. It was observed from DMA results that glass transition temperature (Tg) shows positive deviation at the low molecular weight fraction of 5 %wt in the polystyrene blends.

Pulping of wheat straw by dimethylformamide was studied in order to investigate the effects of the cooking variables temperature (190, 200, and 210°C), time (120, 150, and 180 min), and organic solvent ratio (30, 50, and 70%) of dimethylformamide (DMF+water) value on the degradation of cellulose and delignification of organosolv pulp. The SCAN viscosity was applied to estimate the extent of cellulose degradation produced by cooking condition and it was compared with Kraft pulp at equal content of residual lignin. Response of pulp properties to the process variables were analyzed using statistical software MINITAB 14. The process variables (cooking temperature and time) were set at low variables at high DMF ratio in order to ensure of the low cellulose degradation. Generally, the cooking temperature had a significant effect while the cooking time and DMF ratio had negligible roles. By the comparison of Kraft and organosolv pulps (higher SCAN viscosity of organosolv pulp than Kraft process under equal residual lignin and scanning electron microscopy images) it can be asserted that DMF basically has an improvement role on reducing the cellulose degradation of obtained from pulp. Consequently, the protective action of organosolv on non-cellulosic polysaccharides of wheat straw against degradation under Kraft pulping conditions is considered as the main reason of the fairly high yield of organosolv pulping.

Free-radical melt grafting of the multi-monomer system of maleic anhydride (MAH)/styrene (St) onto polypropylene (PP) was carried out using a singlescrew extruder in the first step. Then melt mixing method was employed to prepare two types of blends, polypropylene(PP)/hyperbranched poly(amide-ester)(HBP) and maleic anhydride grafted polypropylene [PP-g-(MAH-co-St)]/HBP blends. The processability and compatibility of the two blends were investigated as a function of HBP added. Through processing and rheological studies, the results showed that HBP was an effective processing additive. The melt viscosity of the PP/HBP blends dropped in proportion to the amounts of HBP added, and melt viscosity of the PP-g- (MAH-co-St)/HBP blends decreased by the addition of up to 7 %wt HBP, after which the blend viscosity remained essentially constant. Characterization including scanning electron microscopy (SEM), differential scanning calorimetry (DSC,) and Fourier transform infrared spectroscopy (FTIR) data indicated that the HBP formed immiscible blends with PP. A significant degree of compatibilization occurred in the systems of [PP-g-(MAH-co-St)]/HBP, which is evident by shifts in the thermal transitions of the HBP phase and by morphology refinement observed by scanning electron microscopy.

Acomparative study has been made on the isothermal crystallization kinetics and melting behaviour of a metallocene linear low density polyethylene (m-LLDPE) and a metallocene very low density polyethylene (m-VLDPE). The end-surface free energy of the crystal and the lamella thickness distribution were determined for m-LLDPE and m-VLDPE by using the isothermal crystallization rate constants. The degree of short chain branching of both polyethylenes was then calculated and found to be in agreement with the data obtained previously using other methods. Moreover, no distinction could be made between primary and secondary nucleations of the both polymers using the equation proposed by Turnbull and Fisher. Crystallization at a temperature for different time periods has also showed the existence of molecular segregation for both polymers.

The polymeric ligand (resin) was prepared from 2-hydroxy-4-methoxybenzophenone with 1,3-butane diol in presence of polyphosphoric acid as a catalyst at 160oC for 13 h. The poly [(2-hydroxy-4-methoxybenzophenone) 1,3-butylene] H(HMBP-1,3-BD) forms, 1:2 metal:ligand chelates with La (III), Pr (III), Nd (III), Sm (III), Gd (III), Tb (III), and Dy (III). The polymeric ligand and its polychelates were characterized on the basis of elemental analyses, electronic spectra, magnetic susceptibilities, thermogravimetric analysis, and NMR and IR spectroscopies results. The molecular weight was determined using number average molecular weight (Mn) by the vapour pressure osmometry (VPO) method. All the polychelates are paramagnetic in nature. The resin and their polychelates were tested for antimicrobial activity against E. coli, B. substilis, and S. aureus (bacteria) and S. cerevisiae (yeast). It is found that the synthesized polychelates can be used as antibacterial agents.

The present study reveals some aspects on properties of polypropylene (PP) derived from the supported Ziegler-Natta (ZN) catalyst (MgCl2/TiCl4/DEP) and the supported metallocene (MC) catalyst (SiO2/MAO/Et [Ind] 2ZrCl2). Experimentally, PPs were produced using the supported ZN and MC catalysts as mentioned above by varying the conditions such as the polymerization temperatures, propylene pressure, and the [Al]cocatalyst/[Ti]ZN catalyst or [Zr] MC catalyst ratios. Based on the study, it was found that activities, mmmm (%) or isotactivity, and melting temperatures (Tm) apparently depended on the polymerization temperatures, propylene pressures, and [Al] cocatalyst/ [Ti] or [Zr]catalyst ratios in different ways. The impact of each process variable on the properties of PP obtained was further discussed in more details. In general, it was found that the supported MC catalyst provided more active species compared to the supported ZN catalyst leading to higher activities. In particular, the PP produced from the supported MC catalyst also had high isotacticity, however, lower Tm compared to that produced from the supported ZN catalyst. It is worth noting that by changing those parameters, the properties of PP can be altered based on the nature behaviour of the two catalysts. As a matter of fact, the process variables can be chosen in order to achieve the desired properties of PP under the supported catalytic system.

Response surface methodology was used to investigate the kinetics of slurry homopolymerization of ethylene which was catalyzed by soluble metallocene catalytic system of Cp2ZrCl2/MAO. Polymerization temperature, monomer pressure, and molar ratio of cocatalyst to catalyst were considered as the main parameters which affect catalyst activity and viscosity average molecular weight of the final product. A Box-Behnken design was used to produce models for objective responses based on parameters that have significance probabilities (P-value<0.1). It was developed by using the three parameters at three levels including 50, 60, and 70°C for temperature; 2, 4, and 6 bar for pressure; and 3219, 4828.5, and 6438 for molar ratios of cocatalyst to catalyst. Analysis of variance showed that monomer pressure is the most affecting parameter on catalyst activity (P-value<0.0001). It was found that at high levels of cocatalyst concentration, the further increase of its concentration to higher levels decreases the catalyst activity which can be attributed to excessive complexation of MAO with active centres. Polymerization temperature was found to show the significant effect on viscosity average molecular weights of polymers (P-value = 0.0002). It is believed that higher activation energies of chain transfer and deactivation reactions relative to propagation reaction decrease the molecular weight at elevated temperatures. At higher molar ratio of cocatalyst to catalyst, molecular weight also decreases because of more chain transfer to cocatalyst.