Dimitris N. Bikiaris

Synthesis, characterization, and biodegradability of fatty-acid esters of amylose and starch

A series of starch and amylose esters with different degrees of substitution and side-chain length were prepared and studied. The esters were prepared by acyla- tion of the polysaccharide with the appropriate acid chlorides, such as octanoic, dode- canoic, and octadecanoic. The degrees of substitution were 0.54, 1.8, and 2.7. After preparation, the resulting esters were characterized by elemental analysis, 1 H nuclear magnetic resonance ( 1 H-NMR), Fourier transform infrared (FTIR), differential scan- ning (DSC), thermogravimetric analysis (TGA), contact angle, and water uptake mea- surements. Their mechanical properties and, in particular, the tensile strength and elongation at break depend on the side-chain length and on the degree of substitution. The extent of their biodegradability, after exposure to activated sludge, was assessed by weight loss measurements and scanning electron microscopy (SEM). It was found that these new materials are biodegradable, and the biodegradation rate decreases with increasing degree of esterification.

Study of various catalysts in the synthesis of poly(propylene terephthalate) and mathematical modeling of the esterification reaction

Abstract Pure terephthalic acid (TPA) was esterified with 1,3-propanediol (1,3-PDO) in the presence of various catalysts, in order to find the most effective one for this esterification reaction. The prepared oligomers were polycondensated in a second step under high vacuum and using the same catalyst (Sb(OCOCH3)3, Ti(OC4H9)4, GeO2) as before, or the well known catalyst for poly(ethylene terephthalate) (PET) production technology Sb2O3. The esterification reaction was monitored by measuring the distilled water as a function of time and from these data the modeling of this process was carried out. The received poly(propylene terephthalate) (PPT) samples were characterized by viscometry, carboxyl end-group content and color measurement. From this study, tetrabutoxytitanium was proved to be the most effective catalyst for the esterification reaction. When this catalyst was used in the second step a PPT polymer with the highest molecular weight was received.

Effect of carboxylic end groups on thermooxidative stability of PET and PBT

A series of poly(ethylene terephthalate) and of poly(butylene terephthalate) samples containing different amounts of carboxyl end groups were prepared by chain-extension reaction with diepoxides. The effect of the carboxyl content on thermooxidative degradation was studied, using as criteria the induction period of oxidation and the stabilisation coefficient, both obtained by differential scanning calorimetry during isothermal or dynamic heating of the samples under air and nitrogen atmosphere. It was found that as the carboxyl content decreases the thermooxidative stability increases. However, in some more chain extended (crosslinked) samples the thermooxidative stability degreased. This abnormal behaviour was attributed to the lower degree of crystallinity of these samples.

Mechanical properties and morphological examination of isotactic Polypropylene/SiO 2 nanocomposites containing PP-g- MA as compatibilizer

In the present study i-PP/SiO2 nanocomposites, containing 1, 2.5, 5, 7.5, 10 and 15 wt % SiO2 nanoparticles, were prepared by melt mixing on a twin-screw co-rotating extruder. Tensile and impact strength were found to increase and to be mainly affected by the content of silica nanoparticles. A maximum was observed, corresponding to the samples containing 2.5 wt% SiO2. The addition of PP-g-MA resulted in a further enhancement of mechanical properties due to the particle size reduction of silica agglomerates.

Calorimetric study of Diepoxide Chain-Extended Poly(Ethylene Terephthalate)

A series of chain-extended PET samples were obtained by the use of different amounts of a diepoxide as chain extender, which was prepared for this purpose. These samples exhibited different intrinsic viscosities and degrees of branching or cross-linking. The effects of this differentiation on the thermal properties were studied by differential scanning calorimetry. The thermal parameters studied were the glass transition temperature (Tg), the cold-crystallization temperature (Tcc), the melting temperature (Tm), the enthalpy (ΔHm) and the degree of crystallinity. The data revealed that, the higher the quantity of chain extender or the chain extension time, the higher Tgand Tcc, but the lower Tmand ΔHm, i.e. the more amorphous the chain-extended samples, as also shown by density measurements.