Saturated steam autoclaves process

Crimp. The tow is usually relaxed at this point. Relaxation is essential because it gready reduces the tendency for fibrillation and increases the dimensional stabiUty of the fiber. Relaxation also increases fiber elongation and improves dye diffusion rates. This relaxation can be done in-line on Superba equipment or in batches in an autoclave. Generally saturated steam is used because the moisture reduces the process temperatures required. Fiber shrinkage during relaxation ranges from 10 to 40% depending on the temperature used, the polymer composition used for the fiber, and the amount of prior orientation and relaxation. The amount of relaxation is also tailored to the intended apphcation of the fiber product. 

Steam (qv) sterilization specifically means sterilization by moist heat. The process cannot be considered adequate without assurance that complete penetration of saturated steam takes place to all parts and surfaces of the load to be sterilized (Fig. 1). Steam sterilization at 100°C and atmospheric pressure is not considered effective. The process is invariably carried out under higher pressure in autoclaves using saturated steam. The temperature can be as low as 115°C, but is usually 121°C or higher. 

When a container in the conditions noted earlier is sterilized in a conventional autoclave that operates with pure saturated steam, during sterilization a considerable overpressure with respect to the pressure inside the autoclave chamber is generated in the container. This is clearly attributable to the fact that the air (or gas) that was present at filling has remained in the container, whereas the air was eliminated from the autoclave chamber at the beginning of the process. Fig. 4 schematically explains the phenomenon in ideal conditions, i.e., considering air a perfect gas. 

In order to reduce the volume stream and to optimize the efficiency of the following processing units the plastics have to be compacted mechanically before heat/pressure treatment starts. Bales of compacted wet plastics reach bulk densities of about 450 kg/ m3, they are put into moulds which will be transported into autoclaves. During the autoclave process plastics are heated and plastified under saturated steam conditions. Autoclave process is within a wide range independent from changing compositions of the plastics. The process temperature (about 170°C) does not provoke decomposition of plastics, used for household packaging materials. Hydrothermal autoclave conditions lead to further compaction and a stable product (bulk density up to 700 kg/m3) of the mixed different kinds of plastics. Fig. 1 shows a compacted plastic block after finishing the autoclave process. 

A second area of concern associated with steam quality is superheating. This is a phenomenon related to the phase equilibria of steam under pressure (Fig. 1). In some circumstances it is possible at a fixed pressure to increase the temperature of steam above its equilibrium temperature. It is then referred to as superheated or supersaturated steam. Superheated steam is not as effectively lethal to microorganisms as saturated steam—the biochemical mechanisms of lethality are similar to those of dry heat. If supersaturated conditions prevail, the lethality of the process will be much lower at any specified temperature than that which would be expected from saturated steam. Supersaturation may arise from autoclave problems or load problems or both. For instance, the steam in the chamber may pick up heat from a jacket running at loo high a temperature or pressure, or condensation of the steam may be impeded by veiy dry cellulosic materials in the toad. 

Classical sterilisation techniques using an autoclave and saturated steam under pressure, hot water or dry heat are practical and reliable. Other reliable sterilisation methods include membrane filtration, ionising radiatirm sterilisation (gamma and electron-beam radiation) and gas sterilisation (ethylene oxide, formaldehyde). Sterilisation equipment (autoclaves, membrane filters, and other sterilisers) is often used in industrial manufacturing, in preparation in pharmacies, and in other healthcare establishments. Standard sterilisation processes are described in the Ph. Eur., in other current Pharmacopoeias, in ISO standards and National guidelines. 

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