Polyol-Mediated Synthesis of Zinc Oxide Nanorods and Nanocomposites with Poly(methyl methacrylate)

ZnO nanorods (length 30–150 nm) were synthesized in di(ethylene glycol) using Zn(CH3COO)2 as a precursor and para-toluene sulphonic acid, p-TSA, as an end-capping agent. Increasing the concentration of p-TSA above 0.1 M causes the reduction of the ZnO length. Nanocomposites with poly(methyl methacrylate) were prepared using unmodified nanorods. They enhanced the UV absorption of nanocomposites (∼98%) at low ZnO concentrations (0.05–0.1 wt.%), while visible light transparency was high. At concentrations of 1 wt.% and above, nanorods enhanced the thermal stability of nanocomposites. At low concentrations (0.05–0.1 wt.%), they increased the storage modulus of material and shifted Tg towards higher temperatures as shown by dynamic mechanical analysis, DMA, while at higher concentrations (1.0 wt.%) this effect was deteriorated. DMA also showed that spherical ZnO particles have a more pronounced effect on the storage modulus and Tg than nanorods

Istraživanje molekulnih gibanja u poliuretan/polimetakrilatnim interpenetriranim mrežama i smjesama metodom spinske probe

Istražene su djelomice interpenetrirane polimerne mreže (DIPM), te smjese na temelju poliesterskih poliuretana (PU) s karboksilnim skupinama i metakrilatnih kopolimera (PM) s tercijarnim amino skupinama, primjenom elektronske spinske rezonancije, ESR-metode spinske probe. Koncentracije funkcionalnih skupina u pretpolimerima iznose od 0 do 0,45 mmol g-1. Na temelju temperaturno ovisnih složenih ESR spektra odre|eni su heterogenost molekulnih gibanja i fazno razdvajanje u ovisnosti o udjelu funkcionalnih skupina. Probe smještene u domenama s većim slobodnim volumenom odgovaraju brzoj komponenti spektra, dok se sporo gibanje pripisuje probama u prostorima manjega slobodnoga volumena, odnosno staklastim domenama. Iz omjera intenziteta brze i spore komponente utvrđeno je da se povečanjem udjela funkcionalnih skupina smanjuje slobodni volumen u mrežama i smjesama. Smanjenje gibljivosti probe u mrežama u odnosu prema smjesama istoga sastava, posljedica je umreživanja polimernih lanaca. Razlike u molekulnom gibanju probe u ovisnosti o raspoloživome slobodnom volumenu povezuju se s difuzijom malih molekula u polimernoj matrici.The electron spin resonance, ESR-spin probe method was applied to study semi-interpenetrating polymer networks, SIPNs and mixtures on the basis of polyester polyurethanes, PU, with carboxylic groups and methacrylic copolymers, PM, with tertiary amine groups. The concentration of functional groups in prepolymers varied from 0 to 0.45 mmol g-1. From the temperature dependent composite ESR spectra motional heterogeneity and phase separation depending on the functional group concentration were deduced. The spin probes embedded within domains with larger free volume or soft domains correspond to the fast motional component, while the slow motion describes spin probes in the regions of smaller free volume characteristic for the glassy polymers. According to the ratio of fast and slow components, free volume decreases with an increase of functional groups concentration in both polymer mixtures and networks. Restriction of spin probe motion or decreased available free volume in polymer networks in comparison with polymer mixtures of the same composition is a consequence of additional crosslinking in the networks. The differences in spin probe motion due to the available free volume are related to the diffusion of small molecules in polymer matrices

The Influence of Reaction Conditions on the Properties of Graphene Oxide

The present study focuses on correlations between three parameters: (1) graphite particle size, (2) the ratio of graphite to oxidizing agent (KMnO4 ), and (3) the ratio of graphite to acid (H2SO4 and H3PO4 ), with the reaction yield, structure, and properties of graphene oxide (GO). The correlations are a challenge, as these three parameters can hardly be separated from each other due to the variations in the viscosity of the system. The larger the graphite particles, the higher the viscosity of GO. Decreasing the ratio of graphite to KMnO4 from 1:4 to 1:6 generally leads to a higher degree of oxidation and a higher reaction yield. However, the differences are very small. Increasing the graphite-to-acid-volume ratio from 1 g/60 mL to 1 g/80 mL, except for the smallest particles, reduced the degree of oxidation and slightly reduced the reaction yield. However, the reaction yield mainly depends on the extent of purification of GO by water, not on the reaction conditions. The large differences in the thermal decomposition of GO are mainly due to the bulk particle size and less to other parameter

Degradation of PLA/ZnO and PHBV/ZnO composites prepared by melt processing

Composites of polylactide (PLA) or poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and ZnO nanoparticles (nZnO) were prepared by melt processing. During extrusion and moulding nano ZnO formed aggregates with sizes between 0.5 and 5 μm in PLA and between 0.5 and 15 μm in PHBV. Nano ZnO acted as a disruptor of PLA crystallization process and shifted the polymer glass transition temperature to lower temperatures. This was explained by degradation of PLA polymer chains during melt processing. SEC, FTIR and 1H NMR confirmed that PLA degradation was correlated to nZnO concentration. The effect of nZnO on crystallization of PHBV matrix was much less intense which was shown by TGA. On the other hand, PHBV showed significantly lower thermal stability than PLA. ZnO participated as a reactant and an accelerator in the degradation reaction of PLA and at a smaller extent with PHBV. The results of this study revealed that addition of pure nZnO in concentrations higher than 0.1 wt.% is not recommended for the preparation of PLA/nZnO composites by melt processing while in the case of PHBV the nZnO concentration may be higher but it should not exceed 1.0 wt.%. The exposure time of these materials to high temperatures during melt processing should also be minimized

Nanocomposites of LLDPE and Surface-Modified Cellulose Nanocrystals Prepared by Melt Processing

Cellulose nanocrystals (CNCs) were surface modified by esterification in tetrahydrofuran (THF) at 25 °C using different catalysts and anhydrides bearing different alkyl side chain lengths. Unmodified and acetic anhydride (AcAnh)-modified CNCs were studied as potential nanofillers for linear low-density poly(ethylene) (LLDPE). Nanocomposites were prepared by melt processing. Determination of the size and size distribution of CNCs in the nanocomposites by SEM revealed an enhanced compatibility of the AcAnh-modified CNCs with the LLDPE matrix, since the average size of the aggregates of the modified CNCs (0.5–5 μm) was smaller compared to that of the unmodified CNCs (2–20 μm). Tensile test experiments revealed an increase in the nanocomposites’ stiffness and strain at break—by 20% and up to 90%, respectively—at the CNC concentration of 5 wt %, which is close to the critical percolation concentration. Since the CNC nanofiller simultaneously reduced LLDPE crystallinity, the reinforcement effect of CNCs was hampered. Therefore, the molding temperature was increased to 120 °C, and, in this way, the greatest increase of the Young’s modulus was achieved (by ~45%). Despite the enhanced compatibility of the AcAnh-modified CNCs with the LLDPE matrix, no additional effect on the mechanical properties of the nanocomposites was observed in comparison to the unmodified CNC

Nanocomposites with nano-to-sub-micrometer size zinc oxide as an effective UV absorber

Cink (II) oksidne mikročestice (300 nm) i nanočestice (100 nm) su sintetizirane u različitim glikolima i kasnije upotrijebljene za pripravu ZnO/poli(metil-metakrilatnih) nanokompozita. Vrlo niske koncentracije dodanog cink-oksida potpuno apsorbiraju UV svjetlo u području od 290 do 380 nm. Osim odlične apsorpcije u UV području, nano cink-oksid bitno poboljšava stabilnost nanokompozita na sunčevu svjetlost kao i na toplinsku postojanost, dok je submikrometarski ZnO manje učinkovit UV apsorber i toplinski stabilizator od nanometarskog ZnO.Zinc (II) oxide micrometer (300 nm) and nano particles (100 nm) were synthesized in different glycols and were used for the preparation of ZnO/poly(methyl methacrylate) nanocomposites. Very low concentrations of zinc oxide quantitatively absorb UV light in the region between 290 and 380 nm. Besides having extraordinary UV absorption properties, nano zinc oxide also substantially enhances the stability towards sunlight as well as thermal stability of resulting nanocomposites. On the other hand, submicrometer ZnO is less effective UV absorber and thermal stabilizer than nano ZnO