Dried sheet

Sheet Drying. At a water content of ca 1.2—1.9 parts of water per part of fiber, additional water removal by mechanical means is not feasible and evaporative drying must be employed. This is at best an efficient but cosdy process and often is the production botdeneck of papermaking. The dryer section most commonly consists of a series of steam-heated cylinders. Alternate sides of the wet paper are exposed to the hot surface as the sheet passes from cylinder to cylinder. In most cases, except for heavy board, the sheet is held closely against the surface of the dryers by fabrics of carefuUy controUed permeabiHty to steam and air. Heat is transferred from the hot cylinder to the wet sheet, and water evaporates. The water vapor is removed by way of elaborate air systems. Most dryer sections are covered with hoods for coUection and handling of the air, and heat recovery is practiced in cold climates. The final moisture content of the dry sheet usually is 4—10 wt %. 

Curl Control. Many grades of paper tend to cud, especially as humidity varies, because of the stresses produced duting the dryiag process. This is especially troublesome when only one side of the paper receives a surface treatment. Judicious appHcation of water to the opposite side of the dry sheet followed by redryiag may correct the curling. Water may be appHed by surface appHcation at the size press, water box, or calender stack or it may be sprayed on. Small amounts of water can be appHed to the paper surface as a foam with exceUent results. 

Laminates. Laminate manufacture involves the impregnation of a web with a Hquid phenoHc resin in a dip-coating operation. Solvent type, resin concentration, and viscosity determine the degree of fiber penetration. The treated web is dried in an oven and the resin cures, sometimes to the B-stage (semicured). Final resin content is between 30 and 70%. The dry sheet is cut and stacked, ready for lamination. In the curing step, multilayers of laminate are stacked or laid up in a press and cured at 150—175°C for several hours. The resins are generally low molecular weight resoles, which have been neutralized with the salt removed. Common carrier solvents for the varnish include acetone, alcohol, and toluene. Alkylated phenols such as cresols improve flexibiUty and moisture resistance in the fused products. 

Two subgrades of SMR 5 are SMR 5RSS and SMR 5ADS, which are prepared by direct baling of ribbed smoked sheet and air-dried sheet (ADS), respectively. 

TSR 5. Within the Malaysian scheme SMR 5 is restricted to mbber derived from sheet material prepared by conventional processes, ie, ribbed smoked sheet (RSS), air-dried sheet (ADS), and unsmoked sheet (USS) and presented in small bale form. Other countries may source different raw materials, eg, Indonesia produces SIR 5 from thin latex coagulum (14). SMR 5 prepared by pressing dry-sheet material into standard bales must be identified by the type of sheet material, eg, SMR 5RSS, on the test certificate as well as on the wrapping. 

Gas impingement from slots, orifices, and nozzles at 10—100 m/s velocities is used for drying sheets, films, coatings (qv), and thin slabs, and as a secondary heat source on dmm dryers and paper (qv) machine cans. The general relationship for convection heat transfer is (13,14) ... 

Air impingement is commonly employed for drying sheets, film, thin slabs, and coatings. Another application in which it is used is as a secondary heat source on drum and can diyers (see Fig. 12-46). 

This is a material produced from the impregnation of glass fibre-mat (fibreglass, which is in the form of dry sheet, is commonly known as chopped stranded mat (CSM)) or rovings, with a liquid and unsaturated polyester resin, which thickens chemically to a dry sheet form. The total mix is sandwiched between polyethylene films and then roller-pressed to impregnate and consolidate it. 

Chemicals which are used to modify bulk sheet properties usually have to be added to the wet fibre suspension so that they become well distributed throughout the -direction of the sheet. Chemicals which are added as a surface treatment to the dry sheet are usually only able to influence surface properties. 

Equilibrate a second chromatographic chamber with Solvent 2 as described above. The dried sheet is turned to 90° and developed for the second dimension until the solvent front reaches about 5 mm below the top. 

Phosphorescence is observed when the dry sheet is dipped in a container with liquid nitrogen and illuminated by a UV lamp. Purine derivatives phosphoresce light blue pyrimidines are not visible. 

Infrared drying sheets of textiles, paper and films, surface finishes of paints and enamels, and surface drying of bulky nonporous articles. 

Mixt of NC 46.5, NG (or DEGDN) 33.5, PETN (or RDX) 16, St w-insol soap 4% is blended under w and centrifuged to lower the w-content to ca 30%. The soap consists of Caoleate 88, Mg stearate 10 St A1 stearate 2%. The blend is then treated as in Example 1A, but not to complete removal of w. Then, in the middle of rolling operation, some powdered oxidizer (such as Amm or K perchlorate) is incorporated and the material is continued to be rolled to completion of dehydration and gelatinization. The amt of oxidizer is 5 to 45% of dried sheet Example 3 ... 

Natural Rubbers (NR). The chemical name for NR is polyisoprene, which is a homopolymer of isoprene. It has the cis-1,4 configuration. In addition, the polymer contains small amounts of non-rubber substances, notably fatty acids, proteins, and resinous materials that function as mild accelerators and activators for vulcanization. Raw materials for the production of NR must be derived from trees of the Hevea Brasiliensis species. NR is available in a variety of types and grades, including smoked sheets, air-dried sheets, and pale crepes. 

After drying, crack-free tapes could be easily removed from the substrate the green tapes exhibit smooth surfaces, good flexibility and adequate strength (Fig. 6.16). The thickness of the dried sheet was measured to be about 150 pm. The tapes were sintered in a gas pressure furnace at 1800°C for 60 min under 22 bar nitrogen gas pressure. 

The weight expressed in g/m2 of the absolutely dry sheet is correlated with the mesh and solidity, loose papers being lighter and often less resistant to stretch. Normally paper contains some moisture in accordance with the humidity of the atmosphere, about 7 % of dry weight in normal room air and up to 20 c/v in vapor-saturated atmosphere. 

In practice several problems have had to be overcome before this apparently attractive method of sizing could be implemented efficiently. Since the ketene or the anhydride have to react with hydroxyl groups, they will also react readily with water i.e. the molecules are hydrolysed to give non-reacting carboxylic acids (Figure 2). Some means must therefore be found to permit addition of the sizes to the wet-end of a paper machine, and then to ensure that they are retained within the wet paper web in such a way that an adequate size film is deposited on fibres in the dried sheet. This is made more awkward by the essentially hydrophobic nature of the molecules. The means adopted is to prepare emulsions of the sizes, often using cationic starch as a stabiliser and retention aid. 

Air-dried sheets are torn into small pieces to provide a total weight of 3-4g. Screened slush sheets are mixed and 3-4g (dry weight) are made into a pad on a Buchner funnel, taking care to avoid any loss of fibers. The pad is air-dried... 

The patient s skin should be briefly exposed to be able to assess for burn size and depth (see estimation rules). Because burns result in skin loss, the body loses some of its ability to regulate body heat. It is vitally important to keep the patient warm using any means available, such as rescue blankets or dry sheets at the scene and warm blankets at the hospital. Since burned tissue can swell significantly, all constricting clothing... 

Transfer DNA to a nylon membrane as shown in Fig. 7. In a dish of 10X SSC, place a piece of 3MM paper over a platform so that the ends of the paper dip into the buffer and act as wicks. Place the gel on the platform and roll out any bubbles with a pipet. Add a sheet of nylon membrane (prewetted in dH20) and then two sheets of prewetted 3MM paper. Roll out any bubbles between the gel, membrane, and 3MM paper with a pipet. Next add two dry sheets of 3MM paper and a stack of paper towels or blot pads. Add a 500 g weight to the top. Gels are usually transferred overnight, but 4 h is probably sufficient. 

The mass flow rates of the dry sheet and the liquid water in can be calculated from the overall sheet flow rate and the incoming moisture content ... 

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