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EFFECT OF MOISTURE ON THE MECHANICAL PROPERTIES OF NYLON

Extracts from this document...

Introduction

EFFECT OF MOISTURE ON THE MECHANICAL PROPERTIES OF NYLON REPORT BY FAIZAN ANWER HOZEFA NAJEEB PROJECT ADVISOR YASSER JAFFER PREFACE Nylon emerged as commercial thermoplastics after the Second World War following their remarkable wartime success in the textile field. The large scale production of Nylon plastics grew mainly from the adoption of conversion methods and equipment already used for other thermoplastics, together with the availability of relative cheep raw material for bulk manufacture of the polymers. In this report an attempt has been made to present, a broad but balance picture of present day Nylon plastics technology. The topics follow the sequence adapted for monographs on plastic materials in this report and cover raw materials, polymerization techniques, and properties with an historical introduction and testing. While the emphasis is largely based on the effect of moisture on Nylon 6. In discussing properties necessitate is emphasized to obtain the reliable design data to exploit the unique combination of properties possessed by Nylon. In compiling this report a large number of references were consulted, and those from which data were selected for inclusion are listed at the end of the report. SUBJECT Moisture as a matter of fact affects the polymer in respect to their properties and other areas as well, as water molecules may enter the structure of polymer (hygroscopic materials) or may only settle on their surface (hydroscopic materials). In case of hygroscopic materials, as Nylon is, it is very significant to remove the water content from its molecules as they form a primary bond within the polymeric material and hence changes the performance and properties which were expected previously from the polymer. This state of affair raises problems in processing and design of component made from polyamides, for not only most important properties considerably are affected by the water absorption but also the dimensional changes may occur that can affect the functioning of components. ...read more.

Middle

This is done by blowing air heated to a temperature of 550*F through the desiccant beds. The elevated temperature drives the moisture out of the beads and into the ambient air. A multiple desiccant bed absorption system is the most efficient method for drying. A common absorption bed setup is double bed system. In double bed system, one bed is online drying material, while the other bed is in regeneration cycle. There are two types of air flow direction to regenerate desiccant bed: counter-current and co-current. When the desiccant bed is in working mode, the beads act like a sponge with water poured on one side of it. The water does not get dispersed evenly through the bed. Beads that make contact with the wet air will become moist first. Once these beads reach the saturation point, other beads in close proximity become saturated. This process continues until all the beads are saturated. In counter-current regeneration the air flows through the desiccant bed in the opposite direction of working airflow. This forces the moisture out of the desiccant bed opposite the direction in which it entered. The advantage of this is that the bed can be regenerated faster. Dehumidifying dryers are sized similar to the hot air drying system. The hopper is sized by the production rate multiplied by the residence time. The dryer is then sized by the corresponding figures from the dryer sizing chart. The dryers are sized on a flow rate of 50ft/min. If the flow is more than 50ft/min the material will be blown around in the hopper. Any flow rates considerably less than 50ft/min may not have enough velocity to dry the plastic material. Table: Drying times & air velocities for carrousel-type dryers at 160*F (71*C) Nylon Water Time Air velocity % (hr) 120 ft /min.(.057m /sec) 240 ft /min.(.113m /sec) Hopper capacity Output Hopper capacity Output 11 or 12 1 2 260 lb (118 kg) ...read more.

Conclusion

- The thickness of test sample is too much to carry out izod impact for this particular tough polymer. * Observations made during processing of test samples. - While processing specially dried material, it was observed that resin needed a high injection pressure to fill in the cavity, although melt temperature was checked time and again and a bit was increased when needed. This could have been due to over drying of material, which had moisture content of less than 0.094% (which automatically makes resin more viscous). The other possible reason could be the screw used in the injection-molding machine was a conventional type screw, which might regret such hard and crystalline material in flow case. - Splash marks were observed on the molding of undried resin, which might have been because of the volatiles (water) trapment in the barrel. Since the water content level for undried resin was a higher one (3%). The other possible reason could be air trapment in barrel while the hopper feeding wasn't proper or the hopper cover was putted off for a longer period. - A slight color change (yellowish) was observed on the few of the moldings, although they were discarded due to slight over heating. The reason was the same less flow ability shown, especially by dried material. * Market survey. - A local market survey was carried out which made an impression that Nylon wasn't easily available in market and if they do, there isn't enough range of grades and diversity exists. Few of the grades available and their prices are quoted as under: TRADE NAME RATES * ZYTAL (DuPont plastics) 3500/- * NOVAMID (Mitsubishi Plastics) 3750/- * TORAY (1017) 3550/- * U.B.E (1013) 3400/- * Ultramid B35 (BASF Plastics) 3675/- CONCLUSION Polyamides are very much moisture attractive and this moisture content affects a great deal in reducing the mechanical properties of material. The moisture content in polyamides dealt appropriately before processing, in order to achieve the desired and naturally possessed properties of Nylon. ...read more.

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