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All issues / Volume 2 (2008) / Issue 6 (June)

Polymer systems for solid pharmaceuticals
Gy. Marosi
Vol. 2., No.6., Pages 391-391, 2008
DOI: 10.3144/expresspolymlett.2008.46
Macromolecular components of pharmaceuticals represent a segment of small quantity but high value within the polymer market. The knowledge built in these systems act as driving force for other polymer fields. Their conventional role, the coating and bonding, has been extended recently due to new challenges.
On the influence of nucleation on the toughness of iPP/EPR blends with different rubber molecular architectures
C. Grein, M. Gahleitner
Vol. 2., No.6., Pages 392-397, 2008
DOI: 10.3144/expresspolymlett.2008.47
The influence of α-and β-nucleating agents on the fracture performance of two different 32 wt% rubber modified isotactic Polypropylene (iPP) reactor blends is discussed as a function of the phase morphology of the investigated systems. Nucleation for systems with a large inter-particle distance was found to have only a limited impact on the temperature at which the ductile-brittle transition occurs, negative for α-nucleated blends, almost negligible for β-nucleated resins. For blends exhibiting a small inter-particular distance between their ethylene-propylene rubber (EPR) phase, toughness was promoted slightly by α-nucleation and to a large extent by β-nucleation as compared to a non-nucleated reference. These findings raise the importance of mechanistic synergies between the rubbery phase and the matrix to maximize the fracture resistance of blends.
Adhesion property of epoxidized natural rubber (ENR)-based adhesives containing calcium carbonate
B. T. Poh, P. G. Lee, S. C. Chuah
Vol. 2., No.6., Pages 398-403, 2008
DOI: 10.3144/expresspolymlett.2008.48
The adhesion property (i.e. viscosity, loop tack and peel strength) of epoxidized natural rubber (ENR 25 and ENR 50 grade)-based pressure-sensitive adhesive was studied in the presence of calcium carbonate. The range of calcium carbonate loaded was from 10 to 50 parts per hundred parts of rubber (phr). Coumarone-indene resin was used as the tackifier and its concentration was fixed at 80 phr. Toluene was chosen as the solvent throughout the investigation. The substrates (PET film/paper) were coated with the adhesive using a SHEEN hand coater at a coating thickness of 60 µm. Viscosity of the adhesive was measured by a HAAKE Rotary Viscometer whereas loop tack and peel strength were determined by a Llyod Adhesion Tester operating at 30 cm/min. Results show that viscosity of ENR-based adhesives increases gradually with increase in calcium carbonate loading due to the concentration effect of the filler. However, for loop tack and peel strength, it passes through a maximum at 30 phr calcium carbonate, an observation which is attributed to the optimum wettability of adhesive on the substrate at this adhesive composition. ENR 25-based adhesive consistently exhibits higher adhesion property than ENR 50 for all calcium carbonate loadings studied.
Deformation mechanism under essential work of fracture process in polycyclo-olefin materials
T. Kuno, Y. Yamagishi, T. Kawamura, K. Nitta
Vol. 2., No.6., Pages 404-412, 2008
DOI: 10.3144/expresspolymlett.2008.49
The fracture toughness of a glassy polycyclo-olefin (PCO) was investigated by the essential work of fracture (EWF) method using a double-edge notched specimens. It was shown that the PCO follows the EWF concept in the temperature range between room temperature and glass transition temperature Tg where the ligament yielding appear at a maximum point on the stress-displacement curves and subsequently the necking and tearing processes take place in the post yielding region. The essential work of fracture required for the ligament yielding drops as the temperature approaches Tg. The non-essential work of fracture attributed to tearing process after yielding is consumed to expand the plastic region and causes molecular chains to orient to the stretching direction.
The effects of acetylation on properties of flax fibre and its polypropylene composites
A. K. Bledzki, A. A. Mamun, M. Lucka-Gabor, V. S. Gutowski
Vol. 2., No.6., Pages 413-422, 2008
DOI: 10.3144/expresspolymlett.2008.50
Flax fibre was modified with acetylation. The influence of the acetylation on the structure and properties of flax fibre were investigated as well as modified flax fibre reinforced polypropylene composites were also prepared. The catalyst was used to accelerate acetylation reaction rate. Flax fibre was characterised after modification. Surface morphology, moisture absorption property, components content, degree of polymerisation, crystallinity of cellulose and thermal stability of flax fibres were studied. Due to acetylation, the flax fibre surface morphology and moisture resistance properties improved remarkably. Flax fibre (modified and unmodified) reinforced polypropylene composites were fabricated with 30 wt% fibre loading. The mechanical properties were investigated for those composites. Tensile and flexural strengths of composites were found to increase with increasing degree of acetylation up to 18% and then decreased. Charpy impact strengths of composites were found to decrease with increasing degree of acetylation. Owing to addition of coupling agent (maleated polypropylene -MAH), the tensile and flexural strength properties were found to increase in between 20 to 35% depending on degree of acetylation.
Sisal cellulose acetates obtained from heterogeneous reactions
M. Peres de Paula, T. M. Lacerda, E. Frollini
Vol. 2., No.6., Pages 423-428, 2008
DOI: 10.3144/expresspolymlett.2008.51
In the present work, cellulose obtained from sisal, which is a source of rapid growth, was used. Cellulose acetates were produced in heterogeneous medium, using acetic anhydride as esterifying agent and iodine as catalyst, to check if the procedure described in the literature for commercial cellulose also is adequate to sisal cellulose. The results indicated that iodine is an excellent catalyst to obtain sisal cellulose acetates, but the reaction is so fast as described in the literature when, instead of sisal, lower average molar weight cellulose (microcrystalline) is used. The crystallinity index (Ic) of sisal cellulose acetates diminished compared to sisal cellulose, but there was no direct correlation between their degree of substitution (DS) and Ic. Probably acetyl groups were introduced more homogeneously along the short chains of microcrystalline cellulose, when compared to sisal cellulose, and then for microcrystalline cellulose acetates the Ic decreases as DS increases. Using the linear correlation that was found between degree of substitution (DS) and time reaction is possible to control the DS of sisal cellulose acetates, considering a large interval of degrees of substitution (0.3–2.8).
Oxygen barrier property of polypropylene-polyether treated clay nanocomposite
M. Pannirselvam, A. Genovese, M. C. Jollands, S. N. Bhattacharya, R. A. Shanks
Vol. 2., No.6., Pages 429-439, 2008
DOI: 10.3144/expresspolymlett.2008.52
Polypropylene (PP) nanocomposites were obtained by solution blending of polyether treated montmorillonite and PP, with a coupling agent of maleic anhydride grafted polypropylene (PP-g-MA). The composition of the inorganic clay was varied in 1, 2 and 5 phr (parts of clay per hundred of PP by mass) while films of the composites were obtained via compression molding. Wide-angle X-ray scattering (WAXS) showed nanocomposites in which silicate layers were exfoliated and intercalated with respect to the different clay ratios. The morphology and gas permeability of hybrids prepared with organoclay were compared. Morphological studies using transmission electron microscopy showed most clay layers were dispersed uniformly in the PP matrix. Some tactoids of agglomerated nanoparticles were detected, as clay content increased. The oxygen permeability for all the hybrids for clay loadings were reduced by 30% of the corresponding values for pure PP.
Synthesis of a series of soluble main-chain chiral nonracemic poly(alkyl-aryl ketone)
P. Wei, D. Wang, Z. Wu, X. Bi
Vol. 2., No.6., Pages 440-448, 2008
DOI: 10.3144/expresspolymlett.2008.53
A series of main-chain chiral polyketones have been synthesized through condensation polymerization of a dihalide and a diketone with optically pure binaphthyl moiety as linkage in the polymer backbone. The solubility of the polymers can be easily enhanced by substituents at the alpha position next to the carbonyl groups. Reducing the steric hindrance of the substituents in the monomers increases the reactivity of the polymerization. The chiral polymers exhibit large optical rotations. Circular Dichroism (CD) spectra of the polymers are similar to those of the corresponding monomers. The novel synthetic strategy may have great impact on future development of palladium catalyzed condensation polymerizations. The highly soluble chiral polymers synthesized allow for preparation of materials in the form of thin films and have potentials applications in various areas such as chiral separation and recognition.
Synthesis and characterization of hybrid cured poly(ether-urethane)acrylate/titania microcomposites formed from tetraalkoxytitanate precursor
A. L. Tolstov, V. F. Matyushov, D. O. Klymchuk
Vol. 2., No.6., Pages 449-459, 2008
DOI: 10.3144/expresspolymlett.2008.54
Hybrid poly(ether-urethane)acrylate (PEUA)/titania (TiO2) microcomposites were prepared using a novel method that includes a swelling of different photo-crosslinked PEUA networks in concentrated tetraisopropoxytitanate (Ti(OiC3H7)4 or TIPT) precursor solution in organic media followed by the hydrolysis of covalently bonded polyalkoxytitanate ([–OTi(OC3H7)2–]n) chains and their aggregation to amorphous micro- and nano-scale sized TiO2 particles. A formation of polymer/titania hybrids was confirmed by complex investigations of the hybrids using infrared (IR) spectroscopy, small angle X-ray scattering (SAXS) analysis, scanning electron microscopy (SEM) and gravimetry. The dependence of titania phase formation behavior versus functionality of the poly(ether-urethane)acrylate network was discussed. The presence of reactive groups in the organic network promotes the formation of surface-bonded ball-shaped type TiO2 inclusions as well as provides transparency to the hybrid film samples. The results obtained in this work can be applied for the development of polymer/TiO2 composite materials for multipurpose optical application and advanced sealants.
Published by:

Budapest University of Technology and Economics,
Faculty of Mechanical Engineering, Department of Polymer Engineering