M.I. Beltrán

Catalyst addition in polyethylene pyrolysis: Thermogravimetric study

Abstract The effect of catalyst addition on the thermal decomposition of low-density polyethylene has been studied. The pyrolysis has been studied in a thermobalance, using polyethylene mixed with different catalysts, such as MCM41, USY and ZSM-5. The study comprises the analysis of various effects, including the amount of catalyst added and the type of catalyst. It has been observed that almost all the catalytic effect is obtained for a given amount of added catalyst, and a further increase in the catalyst added does not produce a further reduction in the decomposition temperature. A kinetic model has been applied which allows a very good correlation of all the runs performed using the same catalyst. The model involves two different ways for the decomposition, one catalysed and the other non-catalysed. The order of the non-catalysed reaction has been allowed to vary, yielding reaction orders close to zero (i.e. very similar to that found in several thermogravimetric studies of polyethylene decomposition). On the other hand, the catalysed reaction has a rate constant with a saturating dependence with the concentration of the catalyst.

Infrared spectral changes in PVC and plasticized PVC during gelation and fusion

Abstract The behaviour of PVC and PVC plastisols has been studied during their thermal treatment using an in situ FTIR technique. The plasticizer introduces certain modifications in the spectrum of the resin which are more marked in the case of the more compatible plasticizers. The A 1427 A 1435 and A 637 A 616 ratios of the intensities of the crystalline and amorphous bands of the resins, decrease in the plastisols when increasing the compatibility of the plasticizer. On the other hand, when the plastisol undergoes the gelation process, a great decrease of these ratios is observed, showing that the increase in temperature produces a decrease in the amount of the crystalline phase in the resin with respect to the amorphous phase. This behaviour has also been observed when the resin is heated without plasticizer, and is a reversible process. The CO band corresponding to the plasticizer shows a different behaviour to the resin bands. When the temperature increases, a shift to lower wavenumbers is observed. This displacement is irreversible (the band does not recover its original location after cooling) and the process occurs in a relative narrow temperature interval. This temperature range, where the carbonyl band suffers these changes, is in good agreement with the gelation temperature as measured by other techniques.

Effect of the plasticizer concentration and heating rate on the thermal decomposition behaviour of PVC plastisols. Kinetic analysis

The effect of the plasticizer concentration and heating rate has been studied in the decomposition of plasticized PVC. Very interesting aspects related to the different interactions established among the plasticizer and the PVC have been observed. Several kinetic models have been tested to explain the observed behaviour. A great inter-relation has been obtained among the corresponding parameters when separately correlating the data (simultaneously at the four heating rates studied) at each plasticizer concentration. A kinetic model has been developed which is capable of representing simultaneously, with a single set of parameters, the weight loss curves in all the conditions studied.

PVC-plasticizer interactions during the thermal decomposition of PVC plastisols. Influence of the type of plastizicer and resin

The effect of the type of plasticizer and resin on the thermal decomposition of PVC plastisols has been studied by thermogravimetric analysis. Eight plasticizers of different solvent power and ten commercial resins were employed. The shape of the thermograms of the plastisols is strongly influenced by the behaviour of their components. When the plasticizer is in the plastisol, its evolution suffers a delay as compared to when the plasticizer is alone. This behaviour is a consequence of the interactions resulting between the plasticizer and the resin prior to the decomposition process. In the same way, the resin decomposes at lower temperatures when it is in the plastisol. Both effects, the delay in the evolution of the plasticizer and the advance in the decomposition of the resin, are more marked for the more compatible plasticizers. For the more compatible plasticizers, a splitting of the peak corresponding to the resin into two differentiated peaks can be observed in the derivative curve. The first peak has been ascribed to a part of the PVC more susceptible to the plasticizer (i.e. plasticized PVC), while the second probably proceeds from a part of the PVC which suffers less interaction with the plasticizer.

Thermal and mechanical properties of silane‐crosslinked poly(vinylchloride)

A comparative study has been made of the crosslinking of plasticized PVC by grafting of γ-aminopropyltriethoxysilane (ASi) and sodium γ-mercaptopropyltrimethoxysilane (NaMSi) during processing. The influence of type of reagent and concentration, and the rheological behavior were investigated to obtain a crosslinked material with improved mechanical properties and good thermal stability. Depending on the reagent concentration, different gel contents, ranging from 0–100%, were obtained with both reagents. For all crosslinked systems the mechanical properties above Tg were improved. In the case of ASi-crosslinked PVC, the thermal stability deteriorated significantly but, for NaMSi-crosslinked PVC, thermal stability remains close to that of raw PVC, and the separation of the grafting and crosslinking processes is more viable in this case.

Comparative study of the main characteristics and composition of the mainstream smoke of ten cigarette brands sold in Spain.

In this study 10 commercial top selling cigarette brands in Spain have been machine smoked and the mainstream smoke has been analyzed. Multifunctional analysis has been satisfactorily employed to correlate the effect of the main design features of the cigarettes including amount of tobacco, filter size or paper weight with the amount of smoked tobacco and with the ratio CO(2)/CO. The composition of the vapor phase and that of the particulate matter have been analyzed. The particulate matter retained in the filter of the cigarettes has also been analyzed showing a distinct behavior of the compounds condensed in the cigarette filters and in the traps, related to their retention time. A general trend for the relative yield of some compounds in the different brands have been identified and confirmed by multifunctional analysis. Nevertheless, there are some noticeable compounds that behave differently in the different brands.

Thermal decomposition behaviour of crosslinked plasticized PVC

Abstract Thermal stability and thermal decomposition behaviour of plasticized PVC poly (vinyl chloride) and crosslinked plasticized PVC films has been studied. Two effective crosslinking agents have been used: the sodium salt of γ-mercaptopropyltrimethoxysilane (MSi) and γ-aminopropyltriethoxysilane (ASi). Clear differences have been observed in the thermogravimetric behaviour of the different samples. MSi crosslinked films show a certain delay in the decomposition process as compared to plasticized PVC as well as three clear decomposition processes, probably involving the plasticizer and different fractions produced in the crosslinking reactions. In the case of the films prepared with ASi a single decomposition stage is observed at temperatures much lower than those obtained in the other PVC films studied, showing the strong influence of this compound in the thermal behaviour of plasticized PVC. ©

Study of the flow properties and the ageing process in PVC plastisols from commercial PVC resins

The influence of the particle size distribution and the molecular weight distribution in the flow properties and ageing process of commercial PVC plastisols have been studied. An accelerated method to study the interactions between the resin and the plasticizer during the ageing process of the plastisols has been suggested.

PVC plastisols decomposition by FT-IR spectroscopy

A specially designed cell, as described in previous papers, has been used to study the dynamic in situ decomposition of PVC plastisols by FT-IR. The FT-IR spectra provides a new point of view into the intricate problem of the effect of the plasticizers (compatibility and concentration) in the PVC decomposition. A qualitative description of the changes observed in the plastisols spectra is presented. Firstly, the bands due to the plasticizer disappear at temperatures in good accordance with those observed for the plasticizer evaporation in the thermogravimetric decomposition of the PVC plastisol. The plasticizer evaporation leads to a spectrum very similar to that obtained when the PVC is alone at the same temperature. After plasticizer evaporation changes observed in plastisols decomposition are similar to those previously reported with respect to resins decomposition.

The effect of adding processed PVC on the rheology of PVC plastisols

In this paper the possibility of recycling the PVC resulting from the rotational moulding of plastisols is studied. Parts of processed PVC were ground with liquid nitrogen into four fractions of different sizes which were added to a plastisol at different concentrations. A study of the influence of the amount and size of the recycled PVC in the viscosity of the plastisol and in the gelation and fusion processes was carried out. Furthermore, samples were taken at different temperatures and observed by SEM (scanning electron microscopy). Results obtained for plastisols with the recycled PVC show a marked increase in the viscosity and moduli reached during gelation with time, which are more marked as the amount of recycled PVC increase and the particle size decrease. However, plastisols including recycled PVC show and adequate processability if they are used immediately after their preparation.