Evaluation of polyesters from renewable resources as alternatives to the current fossil-based polymers. Phase transitions of poly(butylene 2,5-furan-dicarboxylate)

Poly(butylene 2,5-furan dicarboxylate) (PBF) is an alipharomatic polyester that can be prepared using monomers derived from renewable resources such as 2,5-furan dicarboxylic acid and 1,4-butanediol. In the present work the thermal behavior of PBF was studied. Multiple melting was observed during heating traces of samples isothermally crystallized from the melt using differential scanning calorimetry (DSC). The wide angle X-ray diffraction (WAXD) patterns did not reveal the presence of a second crystal population, or a crystal transition upon heating. DSC study showed that the phenomena are closely related to recrystallization. Temperature modulated DSC (TMDSC) tests indeed evidenced enhanced recrystallization. The equilibrium melting point was estimated to be 184.5 °C using the linear Hoffman–Weeks extrapolation. The heat of fusion of the pure crystalline polymer was found equal to 129 J/g or (27.35 kJ/mol), a little lower than that of PBT. The Lauritzen–Hoffman secondary nucleation theory was used and the surface energy values and the work of chain folding were found to be comparable to those of PBT, but quite lower than those of poly(ethylene terephthalate) (PET). The non-isothermal crystallization on cooling and the cold-crystallization of quenched samples were also studied. Condensed spherulites were observed on isothermal crystallization under large supercoolings by using polarized optical microscopy (POM), while the spherulites turned to ring-banded morphology at higher temperatures. In every case the nucleation density was high.     

Hydrolytic Depolymerization of PET in a Microwave Reactor

Recycling of PET was examined using hydrolytic depolymerization in an alkaline solution under microwave irradiation. The reaction was carried out in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. The main products were the monomers TPA and EG. The effect of reaction temperature, time, amount of PET and alkaline concentration on the degree of PET depolymerization and TPA recovery was investigated. Microwave irradiation was found to reduce the time needed to achieve a specific degradation of PET significantly, with almost complete depolymerization occurring in 30 min at 180 °C and only 46 W of microwave power. Using a phase transfer catalyst (TOMAB) resulted in the same amount of unreacted PET but at significantly lower depolymerization temperatures.

     

Glass-fiber reinforcement of in situ compatibilized polypropylene/polyethylene blends

Polypropylene and low-density polyethylene (LDPE) were melt-blended at proportions 75/25, 50/50, and 25/75 w/w, respectively. These blends were reinforced with two types of glass fibers added at an amount of 20 wt %: the E-type fibers without any surface treatment and the M-type fibers, which were treated with y-methacryloxy propyltrimethoxy silane coupling agent. Poly(propylene-g-maleic anhydride) with 0.8 mol % maleic anhydride content and poly(ethylene-co-vinyl alcohol) with 7.5 mol % vinyl alcohol content were added at a 50/50 w/w proportion as in situ reactive compatibilizers at an amount of 10 wt %. The thermoplastic composite materials have higher tensile strength as well as impact strength compared to the unreinforced blends. The simultaneous process of the in situ blend compatibilization, along with the incorporation of glass fibers in the thermoplastic matrix, leads to a significant improvement of the mechanical properties as compared to the properties of the composite materials with the uncompatibilized matrix. Scanning electron microscopy and micro-Raman spectroscopy have been used to study the adhesion of the thermoplastic matrix onto the glass fibers. Significantly better adhesion characteristics were observed in the composites containing M-type glass fibers, with LDPE adhering the most on the fibers. This better adhesion was reflected in the improved mechanical properties of the composites.     

LDPE/starch blends compatibilized with PE-g-MA copolymers

In the present study, low-density polyethylene (LDPE) and plasticized starch (PLST) blends, containing different percentages of PLST, were prepared. In these blends, two different polyethylene/maleic anhydride graft (PE-g-MA) copolymers containing 0.4 and 0.8 mol % anhydride groups, respectively, were added as compatibilizers at 10 wt % PLST. The compatibilization reaction was followed by FTIR spectroscopy. The morphology of the blends was studied using scanning electron microscopy (SEM). It was found that as the amount of anhydride groups in the copolymers increases a finer dispersion of PLST in the LDPE matrix is achieved. This is reflected in the mechanical properties of the blends and especially in the tensile strength. The blends compatibilized with the PE-g-MA copolymer containing 0.8 mol % anhydride groups have a higher tensile strength, which in all blends, even in those containing 20 and 30 wt % PLST, is similar to that of pure LDPE. The biodegradation of the blends followed the exposure to activated sludge. It was found that the compatibilized blends have only a slightly lower biodegradation rate compared to the uncompatibilized blends. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1503–1521, 1998     

Structure and properties of blends of poly(ethylene-co-vinyl alcohol) with poly(styrene-co-maleic anhydride)

In the present study, ethylene/vinyl alcohol (EVAL) copolymers with different hydroxyl contents were melt mixed with styrene/maleic anhydride (SMA) copolymers. These two copolymers have functional groups capable of reacting intermolecularly, giving stable products. All EVAL copolymers were prepared from the same ethylene/vinyl acetate (EVA) copolymer by controlled hydrolysis. The blends, prepared at constant temperature and rotation speed in the rheomixer, were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermo-gravimetric analysis, as well as mechanical properties and extraction experiments. All the above measurements lead to the conclusion that a certain part of hydroxyls of EVAL have reacted with anhydride groups of SMA, leading to the formation of branched and cross-linked products. The effect of (1) the molar ratio of hydroxyl/maleic anhydride functional groups, (2) the overall concentration of the functional groups, and (3) the mixing time on the structure and properties of the blends are discussed. Emphasis is given on the influence of these factors on the tensile strength, the elongation at break, and impact strength of the products. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 983–999, 1997     

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 acylation of the polysaccharide with the appropriate acid chlorides, such as octanoic, dodecanoic, and octadecanoic. The degrees of substitution were 0.54, 1.8, and 2.7. After preparation, the resulting esters were characterized by elemental analysis, ¹H nuclear magnetic resonance (¹H‐NMR), Fourier transform infrared (FTIR), differential scanning (DSC), thermogravimetric analysis (TGA), contact angle, and water uptake measurements. 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. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1440–1451, 1999     

Use of silane agents and poly(propylene‐g‐maleic anhydride) copolymer as adhesion promoters in glass fiber/polypropylene composites

Two organofunctional silanes and a copolymer were used to increase the interfacial adhesion in glass fiber polypropylene (PP) reinforced composites. The performance of the coupling agents was investigated by means of mechanical property measurements, scanning electron microscopy (SEM), and dynamic mechanical analysis. The increased adhesion between the glass fibers and PP matrix observed with SEM resulted in an improvement of the mechanical and dynamic mechanical properties of the composites. Coupling achieved with the copolymer poly(propylene‐g‐maleic anhydride) (PP‐g‐MA) proved to be the most successful compared with 3‐aminopropyltrimethoxysilane and 3‐aminopropyltriethoxysilane. The combination of PP‐g‐MA with the silanes resulted in further property improvements because of the ability of the MA groups to react with the amino groups of the silanes. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 701–709, 2001     

Altered Distribution and Expression of Syndecan-1 and -4 as an Additional Hallmark in Psoriasis

Syndecans act as independent co-receptors to exert biological activities and their altered function is associated with many pathophysiological conditions. Here, syndecan-1 and -4 were examined in lesional skin of patients with psoriasis. Immunohistochemical staining confirmed altered syndecan-1 distribution and revealed absence of syndecan-4 expression in the epidermis. Fibronectin (FN)—known to influence inflammation and keratinocyte hyperproliferation via α5β1 integrin in psoriasis—was also decreased. Syndecan-1 and -4 expression was analyzed in freshly isolated lesional psoriatic human keratinocytes (PHK) characterized based on their proliferation and differentiation properties. mRNA levels of syndecan-1 were similar between healthy and PHK, while syndecan-4 was significantly decreased. Cell growth and release of the pro-inflammatory Tumor Necrosis Factor-alpha (TNFα) were selectively and significantly induced in PHKs plated on FN. Results from co-culture of healthy keratinocytes and psoriatic fibroblasts led to the speculation that at least one factor released by fibroblasts down-regulate syndecan-1 expression in PHK plated on FN. To assay if biological treatments for psoriasis target keratinocyte proliferation, gelatin-based patches enriched with inteleukin (IL)-17α or TNFα blockers were prepared and tested using a full-thickness healthy epidermal model (Phenion^®). Immunohistochemistry analysis showed that both blockers impacted the localisation of syndecan-1 within the refined epidermis. These results provide evidence that syndecans expression are modified in psoriasis, suggesting that they may represent markers of interest in this pathology.     

Crystallization and melting behavior of three biodegradable poly(alkylene succinates). A comparative study

Polyesters based on succinic acid and respective aliphatic diols, with 2–4 methylene groups were synthesized by melt polycondensation. Crystallization and melting behaviour of samples having the same molecular weight were studied. The odd–even effect was observed for the melting temperatures of these polymers. Poly(propylene succinate) exhibited the slower crystallization rates and lower degree of crystallinity, among these polyesters. In contrast poly(butylene succinate) showed the faster crystallization rates and higher degree of crystallinity. Multiple melting of the isothermally crystallized samples was attributed to partial melting re-crystallization and re-melting, as was revealed by MTDSC measurements and observations at fast DSC heating scans. The equilibrium melting points were found to be 114, 133.5 and 58 °C for PESu, PBSu and PPSu respectively. Also, the corresponding values for enthalpy of fusion were 180, 210 and 140 J/g. Spherulitic growth rates were analysed and the regime transition of PESu and PBSu was studied.     

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

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.