Anhydride chain ends functionalization of poly(ethylene terephthalate)

This paper aims at the end-capping of poly(ethylene terephthalate) (PET) chain-ends in order to introduce anhydride moieties on this polymer. An acid chloride reactive carrier of anhydride was chosen because it selectively reacts by alkoxy-dehalogenation with the hydroxyl chain ends of PET. This type of functionalization has already been described and claimed (1-3) on various polymers. However, in the present paper, a solid-liquid synthesis is reported for the first time: The reaction was performed on solid PET powder swollen in a solvent of the trimellitic anhydride chloride. This new reaction method prevents the polymer from degrading. This point is supported by parallel studies of similar reactions performed in the melt and in solution

Supported dynamic mechanical thermal analysis: an easy, powerful and very sensitive technique to assess thermal properties of polymer, coating and even nanocoating

A dynamic mechanical. thermal analysis (DMTA) performed on stacked coated supports or on samples sandwiched between rigid supports (carbon or glass fibers, metal or glass plates, ...)is described. The choice of a dual cantilever deformation favors the shear strain of the less stiff material between the more rigid supports. A theoretical model demonstrates that the less stiff material response is mainly recorded and moreover amplified. An exceptional sensitivity to the soft material is therefore observed. This method does not require any special sample (only stacking of coated supports or sample sandwiching) whilst it enables to characterize in situ polymer coating, even nanocoating. This characterization is of prime interest in technological coating developments such as paints, fiber sizings, glues, ... This possible measurement of thermal transitions peculiar to nanocoatings also opens more fundamental studies as the probing of interface influence on thermal transitions. (C) 2001 Elsevier Science Ltd. All rights reserved

Polyolefins-biofibre composites: A new way for an industrial production

Low density polyethylene (LDPE) composites based on cellulose fibres have been processed by high shear extrusion with water injection to help dispersion of fibres and release nanofibres from cellulose. Influence of extrusion parameters as shear, residence time, storage conditions of the matrix, and effect of water injection on the morphological properties of the composites have been studied using microscopy. Optimization of the extrusion parameters is necessary to reach a dispersion of the fibres. Increasing shearing forces and residence time allows limiting the presence of large aggregates of cellulose fibres. Use of powdered LDPE, even for short residence time and low shear, is efficient to produce well-dispersed composites. Injection of water during the extrusion also improves the quality of the dispersion. However, no nanofibres are observed. The main effect is a spectacular decrease of the discoloration (yellowing) due to cellulose degradation. Mechanical properties of the composites have been investigated. Young modulus increases with cellulose content and reinforcing effect is more important above 10% by weight. For well-dispersed composites, the extrusion parameters have no significant influence on the stiffness of the composites. However, due to the weakness of the interface, the ductility of composites is reduced compared with LDPE

A comprehensive study of the synergistic flame retardant mechanisms of halloysite in intumescent polypropylene

This work aims to evaluate the efficiency of halloysite as synergistic agent in an intumescent PP system based on a coated ammonium polyphosphate (IFR). The first part of the study analyses the thermal stability and fire performance of PP when using the intumescent formulation alone or in combination with the aluminosilicate nanotubes (HNTs). Cone calorimetry reveals that partial substitution of IFR by HNTs (3 wt.%) imparts substantial improvement in flame retardancy with reduced heat release rate and longer burning times. Additionally, a shift from V-1 to V-0 classification is achieved at the UL-94 test with only 1.5 wt.% HNTs. The second part provides a better understanding of the physical and chemical mechanisms of action of HNTs in the intumescent systems. The chemical evolution of the condensed phase during combustion is described by solid state NMR, and in particular using 2D NMR. Results indicate that halloysite speeds up the development of the intumescent shield, but also enhances its mechanical properties by physical reinforcement (i.e. aluminosilicate “skeleton-frame” for the phosphocarbonaceous structure) and/or by chemical interactions with IFR yielding to aluminophosphates. These new chemical species allow thermal stabilization of the char at high temperatures and provide good macro- and micro-structural properties. Both effects increase the mechanical strength of the protective layer during burning ensuring excellent heat and mass transfer limitations between gas and condensed phases

Kinetics of the thermal and thermo-oxidative degradation of polypropylene/halloysite nanocomposites

In this work, halloysite nanotubes (HNTs) are used to prepare a polypropylene (PP)/HNTs nanocomposite via a melt blending process. The thermal stability of PP/clay nanocomposite compared to virgin PP is investigated in both inert nitrogen and air atmospheres using thermogravimetric analysis. The modelfree isoconversional method according to Friedman is used to estimate activation energies as a function of the conversion degree. The thermal behavior of PP and PP/HNTs 8 wt% nanocomposite is then modeled and simulated. A very good agreement, especially under nitrogen, is obtained between simulated curves and experimental ones, both in dynamic and isothermal conditions. Activation energies of the PP/HNTs nanocomposite increase compared to pure PP, whatever the degradation conditions. These results correlate well with the higher thermal stability of PP observed in presence of halloysite nanotubes, as well as the reduced flammability of PP/HNTs nanocomposites reported in a previous study