Processing Stabilisation of PE with a Natural Antioxidant, Curcumin

The potential use of natural antioxidants for polyolefin stabilisation came into the centre of attention because of some doubts about the effects of the reaction products of synthetic phenolic antioxidants on human health. The effect of curcumin on the melt stability of polyethylene was investigated in this paper with and without a phosphonite stabiliser by using multiple extrusions. Irganox 1010 was applied as reference phenolic antioxidant. Curcumin was characterised by FT-IR and UV-VIS spectroscopy, as well as by thermal analysis. Its stabilisation efficiency was determined by measuring the chemical structure, the rheological properties, the residual thermo-oxidative stability, and the colour of the polymer. The results reveal that the melt stabilising efficiency of curcumin is superior to that of the synthetic antioxidant investigated and is further enhanced by the addition of the phosphonite secondary antioxidant. The changes in the characteristics of the polymer indicate that besides the phenolic OH groups also the linear linkage between the two methoxyphenyl rings of curcumin participates in the stabilisation reactions

Preparation of Highly Porous Scaffolds with Controllable Pore Size from Microbial Polyesters

Microbial polyesters saw limited use in the field of tissue engineering, even though the biocompatibility of these polymers makes them ideal candidates for this role. The primary factor that hinders the proliferation of microbial polyesters in this market is that their processing with conventional techniques, such as electrospinning or 3D printing, is challenging. However, the full potential of these biopolymers could still be utilized by applying unconventional manufacturing methods, such as those based on the concept of salt leaching. An implementation of this concept facilitates the production of scaffolds that simultaneously have high porosity and excellent permeability. Moreover, the average pore size can also be varied in the range from 50 to 400 µm, which was reported to be optimal for the cultivation of eucaryotic cell cultures. By adjusting the pore size, the scaffold can be tailored to the eucaryotic cells the tissue consists of. Furthermore, we have developed an entirely new computational method for the approximation of the pore size distribution of the scaffolds. The method relies on 3D data reconstructed by the software of a digital optical microscope and also facilitates the modeling of the average pore size of scaffolds. Thus, besides the control of the pore size, our method enables its prediction as well

Efficiency of curcumin, a natural antioxidant, in the processing stabilization of PE: concentration effects

The stabilising efficiency of curcumin was studied in polyethylene during processing and under oxygen at high temperature. The effect of the natural antioxidant was investigated at concentrations of 0 to 1000 ppm in combination with a phosphonite secondary antioxidant (Sandostab P-EPQ) of 1000 and 2000 ppm, respectively. The polymer was homogenized with the additives then processed by six consecutive extrusions taking samples after each processing step. The samples were characterized by FT-IR spectroscopy, melt flow index, colour, and OIT measurements. Compared to the effect of pure phosphorous antioxidant, the melt stability of PE is increased already at 5 ppm curcumin content. The melt as well as the high temperature oxidative stability (OIT) of the polymer are controlled by both types of antioxidants. Curcumin hinders the oxidation of polyethylene and the formation of long chain branches during processing, which can be attributed to the fact that curcumin is not only a hydrogen donor but its unsaturated linear moiety can also scavenge alkyl and oxygen centred macroradicals. Curcumin discolours polyethylene already at small concentrations but the colour fades with increasing number of extrusions

Polietilén feldolgozási stabilizálása kvercetin természetes antioxidánssal

A kvercetin stabilizáló hatását vizsgálva Phillips típusú polietilénben megállapítottuk, hogy azonos mennyiségben alkalmazva hatékonyabb, mint az iparban gyakran használt I1010 fenolos antioxidáns. Már 5 ppm esetén mérhető a hatása a folyóképességben, azonban az iparilag elfogadott oxidációs indukciós idő eléréséhez legalább 250 ppm mennyiségben kell alkalmazni. Sárga színe miatt elszínezi a polimert is, így olyan termékekben lehetne felhasználni, melyekben a színező hatás nem okoz értékesíthetőségi problémát

Stabilizátorok hatékonyságának és mechanizmusának tanulmányozása poliolefinekben különböző körülmények között = Study of the efficiency and mechanism of stabilizers in polyolefins under various conditions

A kutatás során a poliolefinek káros kémiai reakcióit (degradáció), valamint a stabilizátorok viselkedését és hatékonyságát befolyásoló tényezőket tanulmányoztuk. Összefüggéseket állapítottunk meg a polietilén gyártási körülményei, a polimer por jellemzői és a feldolgozott polimer tulajdonságai között. Primer (fenolos) és szekunder (foszfortartalmú) antioxidánsok hatékonyságát és hatásmechanizmusát tanulmányoztuk a polietilén feldolgozási körülményei között. Megállapítottuk, hogy a polietilén degradációját elsősorban a foszforstabilizátor reakciói akadályozzák meg, és meghatároztuk a két antioxidáns szinergetikus hatásának az okát. Modell kísérletekkel feltártuk a foszfortartalmú antioxidánsok reakciómechanizmusát és az azt befolyásoló kémiai jellemzőket. Lezártuk az antioxidánsok hidrolitikus stabilitásának meghatározására korábban elkezdett kutatást. A szintetikus antioxidánsok reakciótermékeinek az emberi szervezetre gyakorolt hatásával kapcsolatban felmerült kérdések miatt kiterjesztettük a kutatást a természetes antioxidánsokra (vitaminok, flavonoidok). Ezek pozitív hatása az emberi szervezetre ismert, de (az alfa-tokoferol kivételével) korábban nem foglalkoztak a viselkedésükkel poliolefinekben. A kezdeti sikeres eredményeket követően jelenleg is folytatjuk a kutatást. | In the frame of the project the effects influencing the degradative chemical reactions of polyolefins, as well as the behavior and efficiency of stabilizers were studied. Relationships were established among the polymerization conditions of polyethylene, the characteristics of the polymer powder, and the properties of the polymer processed. The efficiency and the reaction mechanism of primary (phenolic) and secondary (phosphorous) antioxidants were studied under the processing conditions of polyethylene. It was concluded that the reactions of the phosphorous antioxidant hinder the degradation of polyethylene in the first place, and the synergetic effect of the two antioxidants was explained. The reaction mechanisms of phosphorous antioxidants and the chemical characteristics influencing them were explored by model experiments. The study of the hydrolytic stability of antioxidants started earlier was concluded. Because of the doubts concerning the effects of the reaction products of synthetic antioxidants on the human health, the research was extended to the investigation of natural antioxidants (vitamins, flavonoids). Their positive effects on human health is well known, but (except for alpha-tocopherol) their behavior has not been investigated in polyolefins. After the first successes the research is continued

Stabilizátorok hatékonyságának és mechanizmusának tanulmányozása poliolefinekben különböző körülmények között = Study of the efficiency and mechanism of stabilizers in polyolefins under various conditions

A kutatás során a poliolefinek káros kémiai reakcióit (degradáció), valamint a stabilizátorok viselkedését és hatékonyságát befolyásoló tényezőket tanulmányoztuk. Összefüggéseket állapítottunk meg a polietilén gyártási körülményei, a polimer por jellemzői és a feldolgozott polimer tulajdonságai között. Primer (fenolos) és szekunder (foszfortartalmú) antioxidánsok hatékonyságát és hatásmechanizmusát tanulmányoztuk a polietilén feldolgozási körülményei között. Megállapítottuk, hogy a polietilén degradációját elsősorban a foszforstabilizátor reakciói akadályozzák meg, és meghatároztuk a két antioxidáns szinergetikus hatásának az okát. Modell kísérletekkel feltártuk a foszfortartalmú antioxidánsok reakciómechanizmusát és az azt befolyásoló kémiai jellemzőket. Lezártuk az antioxidánsok hidrolitikus stabilitásának meghatározására korábban elkezdett kutatást. A szintetikus antioxidánsok reakciótermékeinek az emberi szervezetre gyakorolt hatásával kapcsolatban felmerült kérdések miatt kiterjesztettük a kutatást a természetes antioxidánsokra (vitaminok, flavonoidok). Ezek pozitív hatása az emberi szervezetre ismert, de (az alfa-tokoferol kivételével) korábban nem foglalkoztak a viselkedésükkel poliolefinekben. A kezdeti sikeres eredményeket követően jelenleg is folytatjuk a kutatást. | In the frame of the project the effects influencing the degradative chemical reactions of polyolefins, as well as the behavior and efficiency of stabilizers were studied. Relationships were established among the polymerization conditions of polyethylene, the characteristics of the polymer powder, and the properties of the polymer processed. The efficiency and the reaction mechanism of primary (phenolic) and secondary (phosphorous) antioxidants were studied under the processing conditions of polyethylene. It was concluded that the reactions of the phosphorous antioxidant hinder the degradation of polyethylene in the first place, and the synergetic effect of the two antioxidants was explained. The reaction mechanisms of phosphorous antioxidants and the chemical characteristics influencing them were explored by model experiments. The study of the hydrolytic stability of antioxidants started earlier was concluded. Because of the doubts concerning the effects of the reaction products of synthetic antioxidants on the human health, the research was extended to the investigation of natural antioxidants (vitamins, flavonoids). Their positive effects on human health is well known, but (except for alpha-tocopherol) their behavior has not been investigated in polyolefins. After the first successes the research is continued

Melt stabilization of PE with natural antioxidants: Comparison of rutin and quercetin

The stabilization effect of a flavonoid type natural antioxidant, rutin, was compared to that of quercetin in polyethylene. Additive concentrations changed between 0 and 500 ppm in several steps and also 1000 ppm Sandostab PEPQ phosphorus secondary stabilizer was added to each compound. Stabilization efficiency was determined by changes in vinyl group content, melt flow rate, oxygen induction time, color and the consumption of the secondary antioxidant during multiple extrusions. The results showed that rutin is as efficient melt stabilizer as quercetin used as reference. On the other hand, rutin has a deteriorating effect on the stability of the polymer at small concentrations and partially decomposes during processing. The comparison of bond dissociation enthalpies indicated that the substitution of the hydroxyl group in the ring C of quercetin by saccharide moieties increases their value, but the small increase does not influence the efficiency of the stabilizer. FTIR and DSC measurements indicated the interaction of the natural antioxidant and the phosphonite secondary stabilizer, and the development of interactions was confirmed by molecular modeling. Mainly hydrogen bonds and aromatic, π electron interactions develop between the hydroxyl groups in ring A and the POC group of the phosphonite, as well as between the aromatic rings of PEPQ and the flavonoids, but they do not influence the stabilization efficiency of the antioxidants

Natural antioxidants as melt stabilizers for PE: Comparison of silymarin and quercetin

The stabilization effect of two flavonoid type natural antioxidants, silymarin (Si) and quercetin (Q), was compared in polyethylene (PE). Additive concentrations changed between 0 and 500 ppm in several steps and 1000 ppm Sandostab PEPQ phosphorus containing secondary stabilizer was also added to each compound. Stabilization efficiency was determined by changes in functional group (vinyl, residual PEPQ) content, melt flow rate (MFR), oxygen induction time (OIT), color and the consumption of the secondary antioxidant during multiple extrusions. The results showed that silymarin is a much less efficient stabilizer in polyethylene than quercetin. The consumption of vinyl groups is faster, melt flow rate and residual stability is smaller in its presence. Silymarin contains less active phenolic hydroxyls than quercetin, but comparison on equal molar basis also shows the inferiority of the compound. The difference can be partially explained by the larger bond dissociation enthalpies of the hydrogens in silymarin, but this antioxidant also accelerates the consumption of the phosphorous secondary stabilizer that must contribute to its smaller efficiency as well. DSC measurements indicate the interaction of the two compounds probably leading to the faster consumption of the phosphorous antioxidant and poor stabilization. Unlike quercetin and dihydromyricetin, the flavonoid type natural antioxidants studied earlier, silymarin is not a good candidate as stabilizer for practical applications