Ivanka G. Popović

The thermogravimetric analysis of some polysiloxanes

Thermogravimetric (TG) and differential thermogravimetric analyses (DTG) of some homo- and copolymers of dimethylsiloxane have been performed. The effect of the presence of hydrido-substituents and/or vinyl end-groups on the thermal and thermo-oxidative stability of the examined polysiloxanes was determined. In all cases it was found that these polysiloxanes are thermally less stable than the parent all-methyl polysiloxane.

The forecasting of municipal waste generation using artificial neural networks and sustainability indicators

The feasibility of modeling municipal waste generation (MWG) for countries at different levels of development using artificial neural networks (ANN) and selected generic indicators of sustainability was investigated. The main goals of this research were to develop ANN-based models for predicting MWG, to overcome the problem of incomplete MWG data, which is notable in developing countries, and to provide a new method for the planning of municipal solid waste management systems as well as for the simulation of various other scenarios. Data from 26 European countries was used in this study as training, test and validation datasets for the developing of ANN models. Since this kind of modeling is particularly important for developing countries where MWG data is missing or incomplete, emphasis was placed on modeling of MWG for Bulgaria and Serbia. Based on a comparison of actual MWG data with predictions given by the model, we show that ANNs can be applied successfully to modeling and forecasting MWG on a national scale. Moreover, the scope for possible application of the model is broad, since it uses generic indicators of sustainability such as gross domestic product, domestic material consumption and resource productivity, and performs well for countries with highly diversified levels of economic development, industrial structure, productivity and output.

The photopolymerisation of methacrylic acid by colloidal semiconductors

SummaryMethacrylic acid was photopolymerised using CdS and composite, CdS/HgS and CdS/TiO2, colloidal semiconductor particles as initiators. The previously proposed photoinitiation mechanism involving the photogenerated positive hole in the valence band of the CdS colloid was confirmed by the electron scavenging action of TiO2. The effect of pH on the course of the polymerisation was investigated and is discussed.

Forecasting of Greenhouse Gas Emissions in Serbia Using Artificial Neural Networks

Serbia is attempting to synchronize its development with the basic assumptions of sustainable development and, consequently, data about environmental impact are necessary. The main goal of this study was to investigate and evaluate the possibility of using the artificial neural network technique for predicting the environmental indicators of sustainable development, in order to overcome the problem of incomplete data and to simulate various development scenarios and their environmental impact. Based on the results obtained, it may be concluded that an artificial neural network can be applied to model the greenhouse gas emissions as one of the environmental parameters of sustainable development.

Thermogravimetric characterisation of poly(methyl methacrylate) photopolymerised by colloidal cadmium sulphide

The thermal stability of poly(methyl methacrylate) (PMMA) photopolymerised using colloidal cadmium sulphide as the photoinitiator was studied by thermogravimetry (TG) and differential TG (DTG).The thermal stability of the CdS initiated PMMA was greater than that of conventional radically polymerised PMMA and approached that of anionically prepared PMMA. The DTG curve of the CdS initiated PMMA was a composite of four peaks, three of which correspond to the three peaks observed in the DTG curve of standard radically prepared PMMA. It is suggested that the additional peak arises from a new mode of depolymerisation initiation, that is, from chain end unsaturation introduced into the polymer chain during polymerisation initiation with the colloidal CdS.

The polymerisation kinetics of lower dialkyl itaconates

SUMMARY: The free radical polymerisation kinetics of diethyl- (DEI), dipropyl- (DnPI), dibutyl- (DnBI), and dihexyl itaconate (DHI) in the bulk were studied in the temperature range from 50 to 70 C. The concentration of the initiator, 2,2 -azoisobutyronitrile (AIBN), was varied between 0.02 and 0.085 mol/dm 3 . The rate of polymerisation (Rp), degree of polymerisation (DP), overall polymerization rate constant (K), the ratio of the propagation and termination rate constants (kp/kt 1/2 ), as well as the chain transfer constant to monomer (CM) were determined. The values of Rp, K, and kp/kt 1/2 of the investigated monomers all increase with increasing size of the alkyl group in the ester substituent, whereas CM decreases when going from the dimethyl to the dihexyl ester. The values of CM are larger than the corresponding values for the alkyl esters of methacrylic acid.

The thermal degradation of some alkali metal salts of poly(itaconic acid)

The Li-, Na- and K salts of poly(itaconic acid) (PIA) were prepared by treating the polyacid with the corresponding aqueous hydroxide.The resulting polysalts were analyzed by elemental analysis, FTIR spectroscopy and thermogravimetry. The results indicate that the polysalts are thermally more stable than the parent PIA, they all degrade in a similar manner and somewhat more complexly than the poly(methacrylic acid) salts.

On the thermolysis of poly(chloroalkyl methacrylates) and poly(chloroalkyl acrylates): Part 1—Poly(2,2,2-trichloroethyl methacrylate)

The thermal degradation of poly(2,2,2-trichloroethyl methacrylate). PTCMA, in the absence and presence of O2 was studied and compared with that of poly(ethyl methacrylate), PEMA. In the absence of O2 the two polymers behaved quite differently. Apart from unzipping, PTCMA became partially insoluble due to intermolecular crosslinking at T 240°C both polymers degraded effectively by depolymerization. O2 prevented crosslinking of PTCMA and retarded unzipping (shift of onset to higher temperature). It was inferred from product analysis that at T < 240°C the thermolysis of PTCMA is initiated by decomposition of pendant groups. Primary bond cleavage at various positions in the side groups, results in the formation of free radicals. In the presence of O2, hydrogen abstraction from CH2 groups in the polymer backbone generates carbon centered radicals which can be converted into oxyl radicals . The latter can give rise to main-chain scission. Apart from the monomer, the main volatile compounds formed in the presence of O2 are: 2,2,2-trichloroethyl pyruvate, CH3COCOOCH2CCl3 and 2-methyl-oxirane carbonic acid 2,2,2-trichloroethyl ester, Mechanisms concerning the initiation of thermolysis of PTCMA are proposed on the basis of the various thermolysis products.

The thermal degradation of poly(di-n-propyl itaconate) and poly(di-iso-propyl itaconate)

The non-oxidative thermal degradation mechanism of poly(di-n-propyl-) (PDnPI) and poly(di-iso-propyl itaconate) (PDiPI) were investigated and compared to the structurally similar polymethacrylates. Analogous to the corresponding polymethacrylates, PDnPI thermally decomposes predominantly by depolymerisation, whereas a considerable amount of side chain scission occurs during the thermal degradation of PDiPI. The thus formed carboxyl groups decarboxylate at elevated temperatures forming a carbonaceous residue.

Cross-linking of highly methoxylated pectin with copper: the specific anion influence

The aim of this work was to investigate the influence of specific anions on the cross-linking process of highly methoxylated pectin using the following copper salts CuSO4; Cu(C2H3O2)2; CuCl2; and Cu(NO3)2 wherein the initial salt concentrations were varied from 0.5 up to 10 g l−1. It was found that the anions affected the sorption capacity wherein the Cu2+ sorption capacity from the sulphate solution was the highest, while it decreased in the presence of CH3COO−, Cl− and NO3− ions, respectively. This difference was mostly pronounced at the higher initial salt concentrations (c0(Cu2+) > 2 g l−1). The obtained beads were characterized by FTIR, AAS, SEM/EDS microanalysis and mechanical compression tests up to 80% of deformation. The sorption data were applied to the Langmuir and Freundlich isotherm models and various calculated parameters confirmed the sulphate anion supportive nature in metal ion binding. The value of the Kf parameter for the cross-linking process of pectin in the presence of acetate, chloride and nitrate was approximately the same (Kf ≈ 0.027 g g−1), while it was higher in the presence of sulphate anions by more than 20% (Kf = 0.0352 g g−1). The predicted 1/n values (1/n 1, 1/n = 1 for the sulphate, nitrate and acetate, and chloride anions, respectively) were the quantitative confirmation of the specific interactions involved in the cross-linking mechanism caused by different anions. The established anion influence was in accordance with the typical ion-specific influence on macromolecules in aqueous systems proposed by Hofmeister.