Thermal Degradation Of Nanocomposites Research Articles

Polydimethylsiloxane‐based Polyurethane/cellulose Nanocrystal Nanocomposites: From Structural Properties Toward Cytotoxicity

Polyurethane/crystalline nanocellulose (PU/CNC) nanocomposites were fabricated through in-situ polymerization by using polydimethylsiloxane (PDMS), methylene diphenyl diisocyanate (MDI), and 1,4-butanediol (BDO) as polyol, aromatic diisocyanate, and chain extender, respectively. CNC content affected the microstructure and thermophysical properties of the nanocomposites. Incorporation of CNCs into PU affected the interactions between soft and hard segments. Although CNCs had slight effect on thermal degradation of nanocomposites, they significantly affected thermophysical properties. For example, CNCs decreased the crystallization of hard segment and glass transition temperatures of hard and soft segments were shifted to higher temperatures. PU showed a relatively high toxicity against human fibroblast cells because of presence of aromatic segments in its structure. Although cytocompatibility was improved by addition of CNCs, PU/CNC nanocomposites showed relatively cytotoxic behavior at higher concentrations.

Polymerization of 2-hydroxyethyl methacrylate by hydro/solvothermal technique in presence of nanographene: electrical and thermal degradation characterization

Nanocomposites of poly(2-hydroxyethyl methacrylate) (PHEMA) loaded with 1.7 mass%, 6.5 mass% and 9.0 mass% nanographene were prepared by hydro/solvothermal technique. The main peaks of the nanographene and amorphous polymer structure were revealed by X-ray diffraction (XRD) analysis. Nanocomposites were characterized by SEM, DSC and TGA techniques. The dielectric constant (eʹ), the dielectric loss factor (eʺ), the loss tangent (tanδ) and the conductivity (σac) were measured using a dielectric analyzer in a frequency range from 100 Hz to 2 kHz. Also, current (I)–voltage (V) measurements were carried out. It is well known that nanocomposite formation causes an improvement of many properties for a polymer, providing enhanced properties such as conductivity and thermal stability. This investigation was done to understand whether the presence of nanographene causes changes in the degradation pathway of poly(HEMA) prepared by hydro/solvothermal technique. For this aim, pure poly(HEMA) and nanocomposites were heated from room temperature to 500 °C. The characterization of degradation products for the cold ring fractions (CRFs) and trapped at − 196 °C (in liquid nitrogen) was investigated by means of FT-IR, 1H, 13C-NMR spectroscopic and GC–MS techniques. The FT-IR, NMR and GC–MS data showed that depolymerization corresponding to monomer (2-hydroxyethyl methacrylate) was the most important product trapped at CRF and − 196 °C in the thermal degradation of nanocomposites. As the nanographene loading increased in composite systems, the rate of depolymerization of poly(HEMA) increased compared to pure poly(HEMA). The nanographene particles in the composite systems acted as a mass barrier that retards the escape of the volatile products

Graphene/Thermoplastic Polyurethane Composites

Thermoplastic polyurethane/graphene nanocomposites were successfully prepared by mixing masterbatches with neat polymers using the melt compounding process. Graphene was obtained from graphite by the chemical mean. Graphite was initially converted into graphite oxide which was then converted to graphene oxide. Graphene oxide was then reduced by L-ascorbic acid to obtain graphene. The effects of graphene addition on thermal and morphological properties of nanocomposite were studied by a differential scanning calorimeter, a thermal gravimetric analyzer and a scanning electron microscope. TPU/graphene nanocomposites showed higher melting temperature compared to TPU. On the other hand, heat of fusion of nanocomposites was lowered. TPU and TPU/graphene nanocomposites have two steps of decomposition. The first degradation of TPU occurred at higher temperature compared with nanocomposites but the second degradation showed the opposite results. The percentage of residue after thermal degradation of nanocomposites was lower than that of TPU. For surface morphology, nanocomposite exhibited the rougher surface comparing with TPU and well graphene dispersion in TPU phase was achieved. Nevertheless, there were some agglomeration of graphene.

The effect of silica nanoparticles, thermal stability, and modeling of the curing kinetics of epoxy/silica nanocomposite

A nanocomposite was synthesized using silica nanoparticles (SN) and Epoxy Vinyl Ester Resin (VE671). Nanoparticles were dispersed in the mixture by ultrasonic equipment to prevent the agglomeration. Transmission electron microscopy was used to investigate the dispersion of the SN in the mixture. Non-isothermal differential scanning calorimetry technique was used to study the cure kinetics of VE671 resin with and without adding SN. The activation energy (Ea) was determined using Kissinger and Ozawa equations. The Ea values of curing for VE671/4 wt% SN system showed a decrease with respect to the neat resin. It means that there is a catalytic effect of SN in the cure reaction. The dynamic curing process was modeled to predict the degree of cure and cure rate of resin using the Sun method. In this method, the results showed a good agreement between the model and the experimental data for different heating rates. Thermal degradation of nanocomposite using thermogravimetric analysis technique was studied. The char yields increased with the addition of 4 wt% of SN to the epoxy resin and improved the polymer flame retardancy and thermal resistance at high temperatures.

Effect of different nanoparticles on thermal decomposition of poly(propylene sebacate)/nanocomposites: Evaluation of mechanisms using TGA and TG–FTIR–GC/MS

Abstract In the present study poly(propylene sebacate) (PPSeb) nanocomposites containing 2 wt% of fumed silica nanoparticles (SiO 2 ) or multiwalled carbon nanotubes (MWCNTs), or montmorillonite (MMT) were prepared by in situ polymerization. The thermal degradation of nanocomposites was studied using thermogravimetric analysis (TGA). It was found that the addition of MWCNTs and MMT enhances the thermal stability of the polymer, while SiO 2 nanoparticles do not affect it. From the variation of the activation energy ( E ) with increasing degree of conversion it was found that the decomposition of nanocomposites proceeded with a complex reaction mechanism with the participation of at least two different steps. To evaluate the thermal decomposition mechanisms and mainly the effect of nanoparticles on the thermal decomposition of PPSeb, TGA/FTIR and a combination of TG-gas chromatography–mass spectrometry (TG/GC–MS) were used. From mass ions detection of the formed decomposition compounds it was found that the decomposition of PPSeb and its nanocomposites, takes place mainly through β -hydrogen bond scission and, secondarily, through α -hydrogen bond scission. The main decomposition products were aldehydes, alcohols, allyl, diallyl, and carboxylic acids.

Effect of P/Si polymeric silsesquioxane and the monomer compound on thermal properties of epoxy nanocomposite

The unique polymeric silsesquioxane/4,4′-diglycidyether bisphenol A (DGEBA) epoxy nanocomposites have been prepared by sol–gel method. The structure of nanocomposites was characterized by attenuated total reflectance (ATR) and solid state 29Si NMR. The characteristic intensity of trisubstituted (T) structure was higher than that of tetrasubstituted (Q) structure from solid state 29Si NMR spectra of 3-isocyanatopropyltriethoxysilane (IPTS) modified epoxy. The activation energies of curing reaction of epoxy system and IPTS modified epoxy system are 28–66 kJ/mol and 57–75 kJ/mol, respectively, by Ozawa’s and Kissinger’s methods. The triethyoxysilane side chain of IPTS modified epoxy might interfere the curing reaction of epoxy/amine and increase the activation energy of curing. The thermal degradation of nanocomposites was investigated by Thermogravimetric analysis (TGA). The char yield of nanocomposites was proportional to the 2-(diphenylphosphino)ethyltriethoxysilane (DPPETES) moiety content at high temperature. A higher char content could inhibit thermal decomposition dramatically and enhance the thermal stability. Moreover, the nanocomposites possess high optical transparency.

The thermal degradation of nanocomposites that contain an oligomeric ammonium cation on the clay

The thermal degradation of polystyrene, high-impact polystyrene, ABS terpolymer, poly(methyl methacrylate), polypropylene and polyethylene nanocomposites has been studied using thermogravimetric analysis coupled to Fourier transform infrared spectroscopy, TGA/FT-IR. The nanocomposites that have been studied include immiscible, intercalated and exfoliated systems and the evolved gases do not depend upon the type of nanocomposite and are qualitatively similar to those of the virgin polymer. In the case of the styrenics, the presence of clay promotes the production of oligomer, rather than monomer. It is suggested that this change in evolved products may offer an explanation for why some polymers give large reduction in peak heat release rates while others give much smaller reductions. According to this notion, any polymer that undergoes degradation to produce both oligomer and monomer should give a large reduction in peak heat release rate.