Berend Eling

Biodegradable materials of poly(l-lactic acid): 1. Melt-spun and solution-spun fibres

Abstract Poly( l -lactic) PLLA fibres with a high degree of molecular orientation and crystallinity were produced by hot-drawing of the melt-spun and solution-spun fibres. Solution-spun fibres show better tensile properties as compared with those of the melt-spun fibres. This may be caused by a lower number of entanglements trapped in the solution-spun fibres. The highest values of the tensile strength found for PLLA fibres in the present study were 0.5 and 1.0 GPa for the melt-spun and solution-spun fibres, respectively. Tensile strength of PLLA fibres increases with the draw ratio, and above a certain molecular weight, also with molecular weight of the polymer. Tensile strength was found to be strongly dependent on the drawing temperature which may be associated with the occurrence of two crystal modifications.

Thermal degradation of polyurethane and polyurethane/expandable graphite coatings

Abstract This study deals with the thermal degradation of polyurethane (PU) and polyurethane/expandable graphite (PU/EG) coatings. EG represents a new generation of intumescent additives which provides good fire retardancy to various materials and in particular to PU. The thermal analyses have shown that the thermo-oxidative degradation as well as the pyrolysis of PU are not affected by the presence of EG. On the other hand, they have enabled the determination of the temperatures which correspond to different steps of the development of the intumescence : formation, stabilisation and degradation of the intumescent shield. Spectroscopic analysis of the residues resulting from each of these steps has demonstrated that the structure of the char is similar for PU and PU/EG and consists in a carbonaceous polyaromatic species. However, the results have suggested that the char formed from PU/EG may contained trapped free radicals.

Analysis of Fire Gases Released from Polyurethane and Fire-Retarded Polyurethane Coatings

We have investigated the analysis of smoke and gases generated under various thermal decomposition conditions of polyurethane (PU) and fire retarded polyurethane coatings. The use of Fourier Transform Infrared Analysis has allowed the continuous detection of a number of the most important fire gases. We have shown that the addition of ammonium polyphosphate (APP) in PU sharply decreases at the same time the emission of toxic gases such as CO or HCN, the optical density of smoke, the weight loss and the formation of soot. Expandable graphite, when added in PU, enables a decrease in toxic gases in a lower proportion than APP. In addition, we note that oxidation reactions strongly influence the nature of the combustion gases in case of fire.

Thermal degradation of urethane modified polyisocyanurate foams based on aliphatic and aromatic polyester polyol

Combustion of polyurethane foams releases toxic gaseous products. Therefore, decreasing the flammability of polyurethane foams is of practical significance to public health and the environment. The reported study investigated the thermal stability of urethane modified polyisocyanurate foams based on the presence of aromatic, aliphatic polyester polyol and polyether polyol moieties. Thermogravimetric analysis and differential scanning calorimetry demonstrated that the foam containing the lowest isocyanate index (220) and the lowest molecular mass of polyether polyol (200) was the most flammable (35% of char residue). Furthermore, the foams which contained a high molecular mass of polyether polyol (2000) and high isocyanate index (460) experienced fire performance (45% of char residue) similar to those foams containing aliphatic and aromatic polyester polyol (41 and 44% of char residue respectively).

Laser pyrolysis/time-of-flight mass spectrometry studies pertinent to the behaviour of flame-retarded polymers in real fire situations

Abstract The Salford Laser Pyrolysis/Time-of-Flight Mass Spectrometry (LP/TOFMS) technique, which models the behaviour in the so-called dark flame region behind the flame front in a polymer fire, has been applied to investigate flame-retarded polymethylmethacrylate (PMMA), rigid polyurethane foam systems and phosphorus retarded rigid polyurethane foams and a model urethane compound. The laser pyrolysis of aluminium oxide trihydrate (ATH) retarded PMMA produces a large amount of water and carbon dioxide in the volatiles. Also, the amount of the monomer evolved is reduced significantly compared to that obtained from pure PMMA. The implication of these results is that in a real fire situation, ATH influences PMMA pyrolysis in such a manner as to bring about a reduction in the evolved “fuel” whilst at the same time adding non-combustible gases (e.g. water) to the flame region. Thus is the PMMA flame retarded. The rigid polyurethane foams studied varied in isocyanate index and the molecular weight of the polyols applied. The flame retardance of these materials has been shown to increase with increasing isocyanate index and weight fraction of isocyanate. Laser pyrolysis experiments of these samples showed that the major volatiles evolved were dominated by monomer and oligomers of the polypropylene glycol used to produce the foam, plus lower molecular weight species of which carbon dioxide appeared to be a significant part. An increase in isocyanate index results in a reduction in the extent of monomer/oligomer evolution and an increase in the low molecular weight species. With reference to the behaviour of the foams in a real fire situation, it could be imagined that the monomer/oligomer components and their breakdown products would act as fuel in the flame region while the low molecular weight species dominated by carbon dioxide would be relatively non-flammable. An increase of isocyanate index is equivalent to making less fuel and more of the “inert gases” available to the burning zone and hence improving the fire resistance of the rigid polyurethane foams. The flame retardant mechanism of phosphorus, introduced as low percentages of dimethyl methylphosphonate, is also attributed to a reduction in fuel evolution via pyrolysis of rigid polyurethane foams.

On the reaction of pendent vinyl groups during chloromethylation of styrene-divinylbenzene copolymers

Abstract In this paper it is shown that during chloromethylation of styrene-divinylbenzene resins of high cross-link density, a side-reaction takes place with unreacted vinyl groups present in the resin. Addition of chloromethyl methyl ether to the vinyl groups results in aliphatic chlorides which differ strongly from aromatic chloromethyl groups in reactivity towards further modification (with, e.g., dimethylamine). This observation explains why IR spectroscopy indicates complete conversion of benzylchloride residues, whereas chlorine is still found by elemental analysis.

Quasiperiodicity and the nanoscopic morphology of some polyurethanes

When straining polyurethane elastomers (PUEs), it is often observed that the long-period peak of the small-angle X-ray scattering (SAXS) does not shift normally. An explanation is indicated for some PUEs in the real-space chord distribution. It exhibits a sequence of constant long-period bands. The band positions form a Fibonacci sequence. This relates to the underlying chemical synthesis by polyaddition of hard and soft modules, indicating a nearly quasiperiodic setup in sequences of stringed hard domains. These sequences appear to be the probes provided by SAXS for the study of morphology evolution in such PUEs. Should a regular-as-possible arrangement of physical crosslinks optimize a property of the material, then in the synthesis the mole fraction nH of hard modules should be chosen to be nH = τ/(1 + τ) ≃ 0.62, where τ is the golden ratio.

Prediction of the rheological properties of reactive polymer systems

A polymerization reaction may lead to either a thermoplastic or thermoset system depending upon the chemical structure of the monomers, and is usually accompanied by a marked increase in viscosity, which is directly related to the extent of reaction. As the molecular weight increases and branch chain structure develops, so a characteristic frequency dependence is observed in the rheology of the system. This paper describes the development of theoretical models which are capable of describing the behaviour of a system in which a condensation polymerization reaction is taking place. Polymerization of difunctional monomers leads to linear polymers, whereas higher functional monomers will ultimately form a three-dimensional network structure. Validation of the models used is achieved by comparing the prediction with experimental data for well defined stable polymer systems. Two sets of materials are studied: firstly, a series of narrow molecular weight linear polystyrenes and secondly, a series of polyisoprene star branched materials. The results of the simulations of the growth of a linear and a branched polymer system are presented, and the implications in relation to the form of the equations used are discussed.

Amine-Free Catalyst Systems for Automotive Instrument Panels

This paper describes the test methods used for assessing the heat stability, the influence of PVC quality and the negative effect of polyurethane foams containing tertiary amine Catalyst. Shortcommings of ICIs new amine-free catalyst. Finally its reactivity and processing behaviour will be illustrated