Effect of temperature and nanoparticle type on hydrolytic degradation of poly(lactic acid) nanocomposites

PLA and its nanocomposite films based on modified montmorillonite (CLO30B) or fluorohectorite (SOM MEE) and unmodified sepiolite (SEPS9) were processed at a clay loading of 5 wt% and hydrolytically degraded at 37 and 58 °C in a pH 7.0 phosphate-buffered solution. An effective hydrolytic degradation for neat PLA and nanocomposites was obtained at both temperatures of degradation, with higher extent at 58 °C due to more extensive micro-structural changes and molecular rearrangements, allowing a higher water absorption into the polymer matrix.The addition of CLO30B and SEPS9 delayed the degradation of PLA at 37 °C due to their inducing PLA crystallization effect and/or to their high water uptake reducing the amount of water available for polymer matrix hydrolysis. The presence of SOM MEE also induced polymer crystallization, but it was also found to catalyze hydrolysis of PLA. Concerning hydrolysis at 58 °C, the presence of any nanoparticle did not significantly affect the degradation trend of PLA, achieving similar molecular weight decreases for all the studied materials. This was related to the easy access of water molecules to the bulk material at this temperature, minimizing the effect of polymer crystallinity clay nature and aspect ratio on the polymer degradation.     

Thermal degradation of polymer-fire retardant mixtures: Part III—Degradation products of polypropylene-chlorinated paraffin mixtures

When polypropylene is thermally degraded in mixtures with a highly chlorinated fire retardant chloroparaffin, a smaller amount of the lighter hydrocarbon fraction, which is also modified in composition, is evolved compared with that evolved from pure polypropylene. A corresponding increase in the amount of high boiling chain fragments is obtained from the mixtures. This effect can be explained in terms of the interactions which occur between degrading polymer and additive.     

Study of the mechanism of intumescence in fire retardant polymers: Part V—Mechanism of formation of gaseous products in the thermal degradation of ammonium polyphosphate

On heating, ammonium polyphosphate eliminates ammonia and water in two successive steps. The first (T = 165–280°C) involves a limited weight loss (ca. 3%) and the formation of some branched structures. The transition from one crystalline form of ammonium polyphosphate to another, more stable, form, may prevent further elimination of NH₃ and H₂O which occurs in the second step (T > 280°C). The final product of degradation is characterised by a crosslinked POP structure formed by elimination of H₂O between POH groups freed by the evolution of NH₃.     

Study of the mechanism of intumescence in fire retardant polymers: Part VI—Mechanism of ester formation in ammonium polyphosphate-pentaerythritol mixtures

It is shown that, on heating ammonium polyphosphate-pentaerythritol mixtures, phosphoric ester bonds are formed first by alcoholysis of the polyphosphate chain. Further intramolecular alcoholysis and/or esterification leads to cyclic pentaerythritol phosphate structures inserted in the polyphosphate chains. Evidence is also given of intermolecular dehydration of pentaerythritol in mixtures with a large excess of alcoholic hydroxy groups over phosphorus atoms. The intumescent behaviour of the mixtures is discussed in relation to the final structure of the product of reaction which depends on the composition of the original mixture.     

Crossed characterisation of polymer-layered silicate (PLS) nanocomposite morphology: TEM, X-ray diffraction, rheology and solid-state nuclear magnetic resonance measurements

As the nanocomposite properties dramatically depend on the dispersion state of the filler in the matrix, it is essential to develop technical methods to characterise the nanodispersion both qualitatively and quantitatively. In this study, complete characterisations of the nanodispersion of organomodified clays in polyamide 6, polypropylene and poly(butylene terephtalate) are presented and discussed using different analytical tools. All four characterisation methods have been evaluated experimentally. TEM has been used to qualitatively characterise the dispersion. As TEM picture might be not fully representative of the whole sample, many pictures have to be analysed to mirror the global repartition. XRD is particularly adapted to the study of intercalated morphology of nanocomposite since the distance between two platelets can be calculated but needs TEM to provide more complete conclusions. Melt rheology and solid-state NMR are bulk analyses. During the measurement the sample is representative of the material. Rheology is relatively simple to make measurements and to get semi-quantitative data. In connection with NMR, we can get quantitative measurements on the degree of nanodispersion in the nanocomposite.     

Thermal degradation of polymer-fire retardant mixtures—Part II: Mechanism of interaction in polypropylene-chlorinated paraffin mixtures

The thermal degradation of polypropylene is accelerated when it is heated in mixtures with a fire retardant chlorinated paraffin (Cl 70%) whose dehydrochlorination rate is simultaneously reduced.The mechanism proposed to account for this behaviour involves the attack of the chlorine atoms, which propagate the dehydrochlorination reaction, on the tertiary hydrogen atoms of polypropylene with formation of HCl. The kinetic chain length of the dehydrochlorination is decreased and the rate of evolution of HCl is lowered, while the radicals formed on the polypropylene chain lead to its scission and volatilisation.The effects of these reactions on the fire retardant performance of the mixture are discussed.     

Study of the mechanism of intumescence in fire retardant polymers: Part III—Effect of urea on the ammonium polyphosphate-pentaerythritol system

Urea, which is commonly used as a ‘blowing’ co-additive in intumescent coatings, is shown to depress intumescence when it is added to ammonium polyphosphate-pentaerythritol mixtures incorporated into the bulk of polypropylene. Concurrently, the fire retardant properties of the intumescent additive are depressed in the presence of urea although, in this case, a smaller amount of flammable hydrocarbons is evolved in the thermal degradation of the polymer.     

Thermal degradation of fire retardant chloroparaffin-metal compound mixtures—Part I: Antimony oxide

The main characteristics of the evolution of HCl and SbCl₃ during the thermal degradation of chloroparaffin-Sb₂O₃ mixtures, which are typical fire retardant additives for polymers, have been studied.Sb₂O₃ reacts with HCl evolved from the chloroparaffin without any apparent effect on the dehydrochlorination process itself. Evolution of SbCl₃ occurs at a maximum rate between 300 and 350°C and is somewhat delayed in the earlier stage of reaction, depending on the composition of the mixture.     

Quantitative extraction of uranium(VI) in aqueous solutions with n-alkylamine intercalates of γ-titanium phosphate

The intercalation compounds Ti(C₃H₇NH₂)(HPO₄)₂·H₂O (18.4 Å) (-TiP/n-Pr) and Ti(C₄H₉NH₂)(HPO₄)₂·H₂O (20.5 Å) (-TiP/n-Bu) have been prepared using -titanium phosphate, Ti(HPO₄)₂·2H₂O (11.6 Å), as precursor. The retention of UO ₂ ²⁺ , in aqueous solutions by -TiP is very low being only a superficial adsorption phenomenon. When the intercalated materials are used, the retention is quantitative until 95% of the cation exchange capacity in the -TiP/n-Pr case (c.e.c.=6.30 mequiv./g), and over 80% for the -TiP/n-Bu compound (c.e.c.=6.04 mequiv./g).