Phenol-crotonaldehyde resins. II. Effect of crotonaldehyde purity on resin properties

Acid-catalyzed polycondensation of phenol and crotonaldehyde results in soluble thermoplastic resins over a broad range of compositions. The thermal and curing behavior of the resins are found to vary markedly with the phenol to crotonaldehyde mole ratio and the purity of crotonaldehyde. Infrared analysis of the resins and their fractions separated by column chromatography indicates that all the resins are structurally similar. The number-average molecular weights of the resins fall in the range of 400 to 600. The resins from distilled crotonaldehyde exhibit higher molecular weights than those from crude crotonaldehyde. The thermal properties of the resins are comparable to the Novolak-type phenol-formaldehyde resins. The thermoplastic nature is retained even at higher fraction of crotonaldehyde, unlike for the conventional Novolak resins

Phenol-crotonaldehyde resins. III. Curing behavior with hexamethylenetetramine

Solid thermoplastic resins were prepared by acid-catalyzed condensation of phenol and crotonaldehyde (both crude and distilled). The thermal and curing properties were compared with the conventional phenol-formaldehyde (PF) novolak resins. Phenol-crotonaldehyde (PC) resins were found to be thermoplastic even after curing with the crosslinking agent hexamethylenetetramine up to 160°C. This curing behavior was observed irrespective of the purity of the crotonaldehyde or the phenol-to-crotonaldehyde mole ratio in the resin. Postcuring of these resins at elevated temperatures yielded insoluble and infusible thermoset products. This unique thermal characteristic could lead to interesting processing possibilities for the resins. The technical feasibility of thermoplastic processing of the PC resins followed by postcure heat treatment for transforming the molded part into a thermoset has been demonstrated

Structure, growth and morphology polyphenylene sulphide

The crystaIIinity, particle size and morphology of polyphenylene sulphide synthesized under various conditions have been investigated by X-ray diffraction and scanning electron microscopy. It was found that crystaIIinity decreased from 71 to 66% with increase of reaction time. The growth of particle size as well as total polymer mass followed a time dependence of the form X = X 0 (1 -e -αt). The particle size distribution curve was noted to be sharp centring at 3 μn for short reaction time, high speed of stirring and also for low concentration of reactants. The particle morphology showed very strong dependence on various reaction parameters. Intricate sheaf-like morphology was noted for the particles at long reaction times or low stirring speeds while oblong platelet type two-dimensional morphology was noted when a low concentration of reactants was used

Rheograms for asphalt from single viscosity measurement

Asphalt materials are used in a variety of applications such as road paving, waterproofing, roofing membranes, adhesive binders, rust proofing and water resistant coatings. There are available in a number of grades distinguished in terms of their softening point and flow resistance. The selection of the proper grade of asphalt for a particular application is governed by the desired flow behaviour. A knowledge of the complete flow curve depicting the variation of melt viscosity with shear rate at the relevant temperatures is necessary not only for proper grade selection, but also for specifying processing conditions for aggregate mixing and spraying. The rheological data are also useful in assessing end use performance. The scientific techniques for generating the rheological data involve the use of expensive, sophisticated instruments. Generation of the necessary flow data using these instruments is beyond the financial and technical means of most processors of asphalt materials. The engineering techniques involving the use of inexpensive vacuum viscometers are relatively easy, but provide a single point viscosity measurement at low shear rate. In the present work, a method is proposed for unifying the viscosity versus shear rate a data at various temperatures for a number of asphalt grades. A master curve has been generated that is independent of the grade of asphalt and the temperature of viscosity measurement. The master curve can be used to generate rheograms at desired temperatures for the asphalt grade of interest, knowing its zero-shear viscosity at that temperature

Rheology of nylon 6 containing metal halides

Addition of metal halides to nylons has been shown to be advantageous in a number of ways. The decrease in melting temperature, increase in glass transition temperature and melt viscosity by such additions have allowed more convenient processing of low molecular weight polymers and thermally unstable polymers. Rheological data depicting the variation of melt viscosity with shear rate at temperatures relevant to processing are necessary in optimizing and trouble-shooting plastics processing operations. In the present paper, a method has been proposed to estimate, complete flow curves or rheograms of nylon-metal halide systems with the use of a master curve knowing the melt flow index and glass transition temperature of the system. The validity of the approach has been verified for the nylon 6-lithium chloride system and shown to hold good for any nylon-metal halide combination

Melt rheology of polymer blends from melt flow index

Polymer blends have received a lot of attention in recent years due to the possibility of getting compounds with novel and/or different properties through proper marriage of the properties of the respective mono-components. The flow behaviour of blends when subjected to stresses is complex and is often found not to vary monotonically with composition. Mixing rules and mixture theories have been used for estimating melt viscosity of a blend at zero shear rate. However a knowledge of the entire rheogram is desirable for process optimization, process design and trouble shooting. In the present paper a method proposed earlier to estimate the rheograms of polymer melts through the use of the melt flow index has been extended to polyblends. A method for obtaining the melt flow index of the polymer blends at various compositions from the melt flow index of the individual components and the blend ratio has been suggested based on the altered free volume state model. Curves that are coalesced using the melt flow index of the blend at different blend ratios have been presented for a polypropylene-high density polyethylene blend, a high density polyethylene-polymethyl methacrylate blend, a polystyrene-polymethyl-methacrylate blend, a polystyrene-polyacetal blend and a polymethylmethacrylate-polyacetal blend

Rheograms for engineering thermoplastics from melt flow index

A method proposed earlier has been extended to estimate complete flow curves or rheograms of engineering plastics. Master curves that are independent of the grade and temperature have been generated and presented for acrylics, polyacetal, nylons, polyethylene terephthalate, polycarbonate and polysulfone. The influence of the various molecular parameters on the viscosity behaviour of polymer melts have been explained rationally. More specifically, the effects of chain branching and of chain rigidity on the master curve of a resin type have been elucidated with reference to polyacetal and polysulfone, respectively. The method presented here can be used effectively by processors of engineering plastics

Management of intra-articular fractures of distal end radius in adults

Background: Incidence of intra articular fracture L/3rd radius is significantly on rise due to high velocity accidents in young and adults. Painless wrist function is of vital importance for functioning of upper extremity in almost all activities of daily living and precise function of hand. Intra articular fracture of L/3rd radius has generally gross comminution and so also small articular fragments. Orthopaedic community differ about specific implants to fix this complex injury. The present study was undertaken to know efficacy of different modalities of treatment for different fracture pattern. Comminuted intra articular fracture geometry varies widely, to fix these small fragments to achieve stable anatomical reduction is a challenging task.   Methods: It is a combined i.e. retrospective and prospective study conducted at Hardikar Hospital, Pune, India from 1999 to December 2000. Patients of intra-articular fracture of distal end radius by different modes of treatment are included in the study. 1 patient with unilateral fracture was lost for follow-up. Thus 50 fractures, in 49 patients. were included in study. Clinico-radiological assessment was carried out by Lidstrom's (1959) criteria.Results: Satisfactory early functional end results with plaster treatment is 72.2% whereas with other modality of treatment it rises to 87.5%, indicating superiority of other modalities of treatment as far as early functional end results are concerned.Conclusions: Manipulation and plaster cast method continues to be the treatment of choice in the stable intra articular distal radial fractures. Hence there is a need for a "differentiated therapy for distal radial fractures". The treatment plan for patients must be based not only on fracture pattern identified on plain radiographs but also on factors such as bone quality, bone comminution, energy of injury and associated soft tissue damage. Additional factors to be considered in individual patient are-life style associated medical conditions and compliance

Structure, growth and morphology of polyphenylene sulphide

The crystallinity, particle size and morphology of polyphenylene sulphide synthesized from 1, 4-dibromobenzene and sodium sulphide have been investigated by X-ray diffraction and scanning electron microscopy. It was found that the crystallinity increased from 62 to 68% with an increase in reaction time. A reordering of crystalline structure with increase of reaction time was also noted. The particle size growth was slower as compared to the reaction rate and the distribution was very sharp. The results are compared with those for polyphenylene sulphide obtained from 1, 4-dichlorobenzene and sodium sulphide