Silane modification of layered silicates and the mechanism of network formation from exfoliated layers

The edges of a synthetic layered silicate, Laponite XLG, was successfully modified with various amounts of ethoxytrimethylsilane, a monofunctional silane compound. The occurrence of the reaction was confirmed with various techniques. Thermogravimetric measurements and Fourier-transform infrared spectroscopy (FTIR) carried out on both the treated filler and the reaction medium yielded a saturation like correlation as a function of the amount of the silane used for treatment. The analysis of the bonded amount of silane by FTIR spectroscopy showed that a side reaction takes place during modification. Although the expected dimerization did not occur, the silane hydrolyzed, thus systematically changing the amount of bonded silane determined from the FTIR absorption of oxygen containing groups. Only vibrations related to the absorption of the SiCH3 group can be used for quantitative analysis. X-ray diffraction (XRD) measurements proved that the silane is bonded onto the surface of the silicate and it does not enter the interlamellar space. Approximately 50 mg silane is bonded to 1 g silicate corresponding to almost complete reaction of the surface OH groups. The results of the measurements were supported by model calculations and extremely good agreement was found between the calculated and the measured values. Surface modification did not hinder the formation of a house-of-card structure showing that the generally accepted mechanism of network formation needs revision. An explanation was offered based on the release of hydroxyl ions from the MgOH moiety of the silicate. The modification of the edges of layered silicates may facilitate exfoliation or help functionalization, but does not prevent network formation and cannot be used for the control of rheological properties

Hidrogélek kölcsönhatása biológiai szempontból jelentős vegyületekkel = Interaction of hydrogels with biologically relevant species in aqueous phase

Az orvosbiológiai és elválasztástechnikai célokra is elterjedten használt reszponzív polimer alapú rendszerekben az anyagfelvételt és -leadást irányító kölcsönhatásokat még mindig nem ismerjük pontosan. Térhálós poli-N-izopropil-akrilamid (PNIPA) hidrogélek fázisátalakulási tulajdonságait különböző biológiailag releváns ionok, aromás molekulák, aminosavak és protein jelenlétében vizsgálva megállapítottuk, hogy hatásuk nemcsak az oldószer ’jóságának’ módosítására vezethető vissza, hanem anyagi minőségüktől függően speciális kölcsönhatás(oka)t alakíthatnak ki a PNIPA oldalláncával. A kölcsönhatásokat befolyásoló tényezők feltérképezésére komplex megközelítést alkalmaztunk (mikrokalorimetria, NMR, szórási módszerek, duzzadási vizsgálatok, mechanikai tulajdonságok, porozitás, stb.). Az irodalomban elsőként publikáltuk a kölcsönható egységek lehetséges konformációit és az atomi távolságokat. Hidrofób módosításokkal kísérletet tettünk a PNIPA gél több tulajdonságának (mechanikai, szorpciós) javítására. A hőmérsékletérzékeny NIPA származékok mellett pH- és redox-érzékeny poli(aszparaginsav) (PASP) géleket is vizsgáltunk. Kettős reszponzív tulajdonságuk, magas víztartalmuk és mechanikai stabilitásuk orvosbiológiai alkalmazásokban előnyös lehet. Kriogén körülmények között NIPA és PASP alapú szupermikropórusos géleket állítottunk elő. Ezek gyors kinetikájuknak köszönhetően igen ígéretesek a célzott és programozott hatóanyagleadásban. | The majority of thermosensitive gels used in biotechnological applications are either homopolymers or co-polymers of N-isopropylacrylamide (NIPA). These applications are based on the ability of PNIPA hydrogels to adsorb, retain and separate different target molecules. The still poorly understood nature of the interactions with small molecules is a vital indicator in understanding a wide variety of systems of biomedical interest. Our observations based on high-resolution DSC, SANS and solid-state NMR converge to show that small aromatic molecules (SAMs) interact with PNIPA hydrogels not only by altering the average solvent quality of the diluent, but also by specific association with the side-chain groups in the NIPA subunits. The effect is strongly influenced by the substituent(s) of the aromatic ring. The most probable conformations and the interactions on atomic level were specified the first time. The potential improvement of the sorption and mechanic properties of PNIPA by hydrophobic modifications was studied. pH and redox responsive poli(aspartic acid) (PASP) gels were also investigated. Their stimuli sensitive properties along with their high water content and good mechanical stability make disulfide cross-linked PASP hydrogels good candidates for human biological applications. NIPA and PASP based supermacroporous polymers were synthesized also in cryogenic conditions. Due to the fast kinetics they are promising vectors for targeted and time controlled drug delivery

Szakmai tevékenység az MNTA TTK Polimer Fizikai Kutatócsoportjában és a BME Műanyag és Gumiipari Laboratóriumában

A Muanyag- és Gumiipari Laboratórium aktívan részt vesz a Budapesti Muszaki és Gazdaságtudományi Egyetem vegyészmérnök és biomérnök képzésében, valamint az országban egyedülálló módon elindítottuk az önálló Muanyag- és Száltechnológiai Mesterszak-ot. Az oktatás mellett, kutatócsoportunk a polimerek feldolgozásához és alkalmazási területeihez kapcsolódóan végez szerteágazó kutatómunkát

A colourimetric method for the determination of the degree of chemical cross-linking in aspartic acid-based polymer gels.

A 2,4,6-trinitrobenzenesulphonic acid (TNBS)-based assay is developed to determine the degree of chemical cross-linking in aspartic acid-based polymer gels. The conventional colourimetric method for the quantitative determination of amine groups is difficult to use in polymer networks; thus, an improved method is developed to analyse polymer gels swollen in dimethyl sulfoxide (DMSO). Reaction products of the derivatizing reaction are examined by NMR. The chemical stability of the reagent is increased in DMSO, and the method shows satisfactory linearity and accuracy. The degree of chemical cross-linking in the investigated gels is close to its theoretical maximum, but the conversion of the pendant amine groups to cross-linking points is strongly dependent on the feed composition of the gels

Determination of the specific surface area of layered silicates by methylene blue adsorption: The role of structure, pH and layer charge

The specific surface area of three layered silicates was determined by three independent methods; it was estimated from the average dimensions of individual silicate layers, determined by nitrogen adsorption using the BET model and calculated from the adsorption of methylene blue on their surface in aqueous sol. The BET model gave smaller surface areas than expected, because nitrogen molecules cannot penetrate freely into the interlayer space of the silicates. Geometric calculations and the methylene blue approach yielded very similar values for two different types of Laponite when the pH of the dispersion was adjusted to 6.5 or the edges of the silicate were modified with tetrasodium pyrophosphate dispersing agent. The measurement of surface area in water without the control of pH yielded smaller surface area, because methylene blue decreased the pH of the solution resulting in the competitive adsorption of methylene blue cations and protons at the basal surface. The methylene blue approach resulted in larger surface area than expected for the silicate with large ion exchange capacity, because of the tilted orientation of the adsorbed methylene blue molecules. All these factors must be considered during the use of the methylene blue method for the determination of the specific surface area of smectites

4. szekció: Új eszközök, módszerek és megközelitések a segitő szakmákban

Kulcskérdések a mai magyar szociálpolitikában és a változtatás lehetőségei - Zárókonferencia az ELTE Társadadalomtudományi Kar, a Hilscher Rezső Szociálpolitikai Egyesület, a Gyere Egyesület és a Care Europe szervezésében 102. o. Hegyesi Gábor összefoglalója a szekció munkájáról 108. o. Barcy Magdolna – Kenderfi Miklós – Hegyi-Halmos Nóra workshopj

Enzymatic degradation of PLA/cellulose nanocrystal composites

The enzymatic degradation of poly (lactic acid) (PLA) and its nanocomposites reinforced with cellulose nanocrystals (CNC) was catalyzed with lipase from Candida rugosa and proteinase K from Tritirachium album. The composites were prepared with the Pickering emulsion process and they contained 5, 10 and 15 wt% nanocellulose. Compression molded plates were cut to pieces for the degradation experiments. Preliminary experiments showed that the lipase does not catalyze the degradation of PLA, but the proteinase K is very efficient. The lactic acid forming during the reaction decreases the pH of the degradation medium almost to 4 that leads to the denaturation of the enzyme. Besides pH, the ion concentration of the solution also influences the rate of degradation; smaller ionic strength is more advantageous. The cellulose nanocrystals used for the reinforcement of PLA increase the rate of degradation and the samples disintegrate very rapidly, the polymer degrades in three days. Because the samples lose their integrity, also the amount of lactic acid forming in the process was determined with a colorimetric assay with iron (III) chloride hexahydrate to follow degradation. A model was applied for the quantitative analysis of the kinetics of degradation and denaturation. The rate of both processes doubles in the presence of cellulose nanocrystals. The model and the obtained parameters can be used for the design of experiments and the prediction of the enzymatic degradation of aliphatic polyesters as well as their blends and composites

Preparation and characterization of PVA/GA/Laponite membranes to enhance pervaporation desalination performance

Pervaporation (PV) has shown great promise in water desalination technology. In this work, laponite XLG - Poly (vinyl alcohol) (PVA-Lap) mixed matrix membranes (MMMs) were fabricated to investigate the elaboration of desalination of high-salinity water by pervaporation. The influence of laponite content on the morphology, chemical structure and hydrophilicity of the membranes was investigated. In addition, salt transport properties in the membranes were observed. Moreover, the effect of different laponite content in the PVA matrix on the desalination performance was observed at temperatures from 40°C to 70 °C and feed solutions with up to 10 wt% NaCl. The prepared MMMs showed higher hydrophilicity and roughness of the surface and higher mechanical stability. The higher water flux of 58.6 kg/m2.h with a salt rejection over 99.9 % was achieved using 2 wt% laponite XLG MMMs desalinating 3 wt% aqueous NaCl solution at 70 °C. The salt permeability in the membrane was lower by two orders of magnitude than that of water. The water/salt selectivity increased, while the water permeability decreased, with increasing of laponite content in the membrane

Poly(lactic acid)/lignin blends prepared with the Pickering emulsion template method

In this work, the Pickering emulsion template method was used to introduce lignin nanoparticles into poly(lactic acid) (PLA) with improved dispersion. The effect of lignin as the stabilizer of Pickering emulsions was studied in this paper, including the thermal, rheological and mechanical properties of the blends. The PLA/lignin films had reduced light transmission in the UV light region, and Young’s modulus of PLA/lignin blends increased, while their tensile strength and elongation-at-break decreased as compared to neat PLA film. The introduction of lignin improved crystallinity of PLA from 7.5% to over 15%, and increased its decomposition temperature by about 10 °C. The lignin in the blends prepared using the Pickering emulsion template approach had much larger load bearing capacity than the dispersed lignin particles in the usual melt blended material. All the results indicated that the Pickering emulsion template method improves the dispersion of lignin (over 5.0 wt%) in PLA and improves UV protection, crystallinity, decomposition temperature and Young’s modulus of PLA

Poli(metil-metakrilát) rögzítése ionosan rétegszilikátok felületén nanokompozit töltőanyagként való alkalmazásra

A szmektit nanokompozitok kutatása során eddig nem sikerült áttörést elérni, mert a szilikátok szétválasztása egyedi lemezekre kizárólag vízben valósítható meg, ahol az egyes lemezek között elektromos taszítás alakul ki. A kompozitokat azonban nem vizes közegben, hanem monomerben duzzasztva vagy ömledék állapotban állítják elő, ahol taszító kölcsönhatások nem lépnek fel. Emellett az ömledékben fellépő nagy nyíróerők sem képesek a lemezek szétválasztására a gyenge polimer-szilikát kölcsönhatás miatt. Olyan felületkezelési módszer dolgoztunk ki, mellyel a nagy polimerizációs fokú polimer ionosan rögzíthető a szilikát felületén