Iranian Polymer Journal
Year:2007 | Volume:16 | Issue:7|Papers Count:7

Poly(vinyl alcohol) (PVA) is a water soluble polymer with excellent physical and chemical properties. The basic properties of this polymer depend on its molecular weight, degree of hydrolysis and distribution. Since the commercial applications of PVA are many and varied, therefore, a special grade of PVA with considerable properties is required as an emulsifier. A polymerized ester can be used for preparation of PVA types, because vinylalcohol monomer does not exist in the free state. The characteristics of the preparation of poly(vinyl acetate) (PVAc) are very important in the manufacture of PVA. In this work, a partially hydrolyzed grade of PVA having characteristics suitable for application in emulsion polymerization of vinyl acetate (VAc) (Mv: 77200, hydrolysis degree: 89.2%) was prepared by investigation of reaction conditions for solution polymerization of VAc by the aids of α,α' azobisisobutyronitrile (AIBN) initiator in methanol and the subsequent saponification reaction of the resulted PVAc in the presence of NaOH. This was including investigation of the effect of [VAc]/[AIBN] ratio and polymerization time for preparation of PVAc at 60°C in terms of VAc conversion and PVAc molecular weight, then the effect of saponification time of PVAc in terms of the molecular weight and hydrolysis degree of PVA product. In case of some samples, concentration of the monomer relative to that of the initiator plays an important role in VAc conversion value and controlling the PVAc molecular weight. The results from saponification of PVAc samples revealed that, only one of the samples was that its saponification resulted in PVA material desired molecular weight at 1 h. 1H NMR Spectra of PVAc and PVA were used to show a branched molecular structure of PVAc and estimation of the degree of hydrolysis of a PVA sample. The presence of typical characteristics absorption bands in IR spectra of PVAc and PVA samples agrees with proposed structures. To confirm the result earned, the characteristics of PVA obtained were compared with those of the commercially used PVA grades (Mowiols).

Polypropylene/poly (ethylene-co-propylene) in-reactor blends were synthesized by sequential multi-stage polymerization technique using fifth generation of Ziegler-Natta catalyst. Blends of isotactic polypropylene (iPP) (with a minimum isotacticity index (II) of 97.5%) and at least 12% ethylene/propylene copolymer were successfully synthesized. Experimental set-up and polymerization procedure are described in detail. Effect of external electron donor on catalyst behaviour was studied. The results showed that for the catalytic system investigated, using external electron donor causes a decrease in catalyst hydrogen response and productivity at both homo and copolymerization stages and an increase in the ratio between amorphous to crystalline ethylene-propylene copolymer of the blend. Furthermore, increasing the proportion of C2 in the copolymerization stage leads to increase of both polymerization rates and the amount of ethylene/propylene rubber (EPR) in the blend.

Nylon 6 and 66 were toughened with EPDM-g-MA and SEBS-g-MA and steadystate rheological behaviour of rubbers, nylons and their blends and mechanical properties of nylons and their rubber-toughened blends were investigated. The EPDM maleic grafting preparation was performed in the framework of this study where SEBS-g-MA was obtained from a commercial source. The results showed the ultratoughened SEBS-g-MA blends, whereas EPDM blends under the same blending conditions did not show a significant improvement in toughness. In case of EPDM toughened blends an average of some micrometers was observed for the dispersed EPDM particles. Impact and tensile properties of the toughened blend with 20% of SEBS-g- MA rubber showed about 1540% improvement in impact and 240% in elongation-atbreak of the blend as compared with those of neat nylon, whereas these properties only showed 30% reduction in Young's modulus of the blends. Rheological measurements revealed the closeness of the viscosity of SEBS-g-MA and nylon 66, whereas the viscosities of EPDM rubber and nylons were found very far from each other under the blending conditions. Morphological observations using SEM technique revealed a co-continuous and a probable nano-scale-dispersed SEBS-g-MA in nylon matrix.

This study highlights the utilization of linseed oil epoxy (LOE) (a product from a sustainable resource), to obtain blends of LOE with polystyrene (PS) forming tough and flexible free-standing films. The blends were prepared by mechanical mixing of the requisite amounts of the two components in the weight ratios of LOE/PS are 85/15, 65/35, 55/45, 45/55, 35/65, and 15/85 through a solution method by mixing in tetrahydrofuran. Free-standing films of the blend were cast. The miscibility of the two components in a solution phase was investigated by reduced as well as relative viscosities and density measurements while the miscibility in a solid phase was examined by scanning electron microscopy (SEM). At all the concentrations, calculated values of reduced viscosity were found to be higher than the observed values of the reduced viscosity for the blends with 15-85 wt% of PS. Viscosity measurements reveal that miscibility occurs between the composition range of LOE/PS 85/15 to 45/55. At composition LOE/PS 35/65, phase inversion takes place which indicates the onset of immiscibility of the two components in the solution phase. The immiscibility of the two compositions at this composition (LOE/PS 35/65) is also shown by the SEM micrographs which exhibits two distinct phases. The mechanical properties of LOE/PS blend films were found to match with LDPE at composition LOE/PS 65/35. The potential applications for such sustainable resource based blend include packaging films and production biodegradable plastic sheets which can be formed into products such as bio-bags.

In this study, mechanical properties of high density polyethylene (HDPE) and polypropylene (PP)-wood flour composite (WFC) decking boards were evaluated and the effect of maleated polypropylene (MAPP) as a coupling agent was investigated. Decking boards were manufactured using Davis-Standard® WT-94 WoodtruderTM. Flexural, tensile and impact properties of the decking boards were evaluated. Fractured surface of samples were also studied using scanning electron microscope. Results showed that PP-WFC decking boards provided higher tensile and flexural properties than HDPE-WFC decking boards. The use of maleated polypropylene (MAPP) coupling agent significantly increased the tensile strength and tensile modulus of both HDPE-WFC and PP-WFC composite decking boards. In the case of flexural properties, MAPP coupling agent slightly increased the flexural strength of HDPE-WFC but did not affect the flexural modulus of HDPE-WFC, and flexural strength and flexural modulus of PP-WFC decking boards. This study showed that MAPP coupling agent can effectively be used as a coupling agent for HDPE base resin. It is believed that this performance is due to the base resin used in this study since it is a narrow molecular weight hexene copolymer HDPE. Both HDPE-WFC and PP-WFC decking boards, even with no coupling agent, provided flexural properties required by the ASTM standard for polyolefin-based plastic lumber decking boards. In the case Izod impact strength, addition of MAPP coupling agent significantly reduced the notched Izod impact strength of the all decking boards. In addition, morphological study showed that compatibility between the wood flour and the plastic matrix were improved with the use of MAPP coupling agent.

Random copolymers of L-lactide, glycolide and trimethylene carbonate were synthesized by bulk ring-opening copolymerization of monomers in the presence of stannous octoate as catalyst at 120°C for 48 h. Glycolide and L-lactide were prepared from their parent acids and then purified by multiple recrystallizations from ethyl acetate. Six copolymers with various mole% of the monomers were prepared and characterized. 1H NMR and 13C NMR spectra of copolymers that were recorded show the random character of the materials. Each 1H NMR and 13C NMR signal split to several peaks. Thermal behaviours of the copolymers were evaluated by DSC thermograms. Copolymers that contain L-lactide and trimethylene carbonate show an endotherm in DSC, but those containing three monomers do not show any transition in DSC. Mechanical properties of the copolymers were evaluated by measuring stress-strain curves of film specimens prepared by solvent casting.

The linear copolymer of styrene (ST) and carbon monoxide (CO) was prepared in the presence of palladium acetate, cupric p-toluenesulphonate and rare earth acetate RE(OAc)3 (RE= Pr, Nd, Eu, Dy, Ho) multiplex catalyst system. The structure of products was characterized by 13C NMR and FTIR. It is found that the catalytic activity of the system increases with the increasing of atomic number and decreasing of the ionic radius from praseodymium to holmium. The best catalytic effect was obtained when the molar ratio of Pd2+: Ho3+: Cu2+ was 1:4:4, and the catalytic activity was 1194 g/(gPd·h). The effects of the different components including methanol, 2,2-bipyridyl, p-toluenesulphonic acid, and p-benzoquinone on the copolymerization were also studied in detail. To evaluate the influence of different components on the catalyst system, the principal component analysis method was employed. The experiments and data analysis performed have shown that three principal components are significant for evaluation of total variability of the catalytic system.