Surface strength

In papemiaking, chemicals can be added either to the pulp slurry prior to sheet formation, ie, internal or wet-end addition, or to the resulting sheet after complete or partial drying, ie, surface or dry-end addition. The method chosen depends on retention and the desired effect. For example, strength additives usually are added internally if uniform strength throughout the sheet is wanted, but they are applied to the surface if the need is for increased surface strength. If an additive caimot be retained efftciendy from a dilute pulp slurry, then it is better to apply it to the surface of the sheet. 

Starches used to increase the internal strength of paper as measured by tensile, edge cmsh resistance, Mullen burst, and Scott bond strength are added at the wet end, whereas starch used to increase surface strength as measured by pick and resistance to Hnting are added at the size press. 

Lighdy derivatized starch acetates are employed in food because of the clarity of their gels and their stabiHty. AppHcations include frozen fmit pies and gravies, baked goods, instant puddings, and pie fillings. Starch acetates are used in textiles as warp sizes and in paper to improve printabiHty, surface strength, and solvent resistance. 

Surface Sizing. Surface sizing is generally used for modification of other properties of paper or paperboard such as printabiHty, smoothness, porosity, coefficient of friction, opacity, surface strength, anti-linting or coating holdout. Anionic starch is perhaps the most common additive or co-additive used for surface sizing. 

J. M. Szymanski (1973, 1979) successfully applied Scott s method to surface strength tests with plaster casts. A near-surface layer of higher strength in relation to the interior of the cast was found to develop while the casts were drying (Fig. 4.4.5). The concept of laminar abrasion resistance WSic was introduced and defined as the reciprocal of the derivative of a function Am — that is,... 

One of the most popular high-temperature sensors is the platinum thermocouples, which are usually installed inside protective thermowells or protection tubes. When installed horizontally, wells tend to droop, causing binding of the TC element, making replacement difficult. The latest designs incorporate a sheath with a flexible cable that can easily be inserted into even badly drooping wells. Ceramic wells do not suffer from droop but have other limitations such as low surface strength, brittleness, and low erosion resistance. 

In past practice, native (unmodified) starch was added to the papermaking furnish in order to increase internal and surface strength of the product. The presence of starch in the papermaking furnish allows lower levels of pulp refining for... 

Starch is added to the papermaking furnish for a variety of applications paper formation control furnish drainage improvement filler and cellulose fines retention size retention internal paper strength improvement surface strength enhancement and reduction of waste water pollution. 

An alternative method to apply starch to paper, especially to paperboard grades, is to use a water box at the calender. Water boxes are used for wet-finishing of paper-board prior to coating application. Use of starch in the water box will increase surface strength and lessen fiber reswelling after coating application. Dilute dispersions of oxidized starch are used, frequently in conjunction with a lubricant to prevent calender roll picking. 

Apart from the lubricant area fraction, the actual dimensions of the recesses are also important. Deep, narrow pockets are inherently likely to give strong support and retention of the lubricant material, but, as shown previously, deep pockets are wasteful of lubricant, while narrow pockets are susceptible to blocking with wear debris. On the other hand, wide shallow pockets are likely to provide poorer support and retention for the lubricant material. Wide recesses will also lead to a gross lack of uniformity in the surface strength of the bearing surface because the lubricant composite and the metal matrix are likely to have very different moduli. 

A separate section of this book discusses the selection and design of substrate structures which are required to support chemically-resistant masonry. This section will not duplicate what appears therein, except to warn the designer of three things. (1) The designer must verify that the substrate selection and design are adequate to provide the necessary support for the full load anticipated with a safety factor of not less than 1V2, without visible deflection. (2) He must check with the materials manufacturers and installers of all the materials he has selected which will be in direct contact with the substrate to determine what surface strength and surface preparations of the substrate should be provided, and then be certain that these requirements are included in his specifications. (3) He must verify that there is nothing in the materials that will be in contact... 

Common starch esters include the acetates. High d.s. starch acetates have been formed by using acetic anhydride with either sodium acetate or pyridine catalysts at 90-100 °C [158,159,160]. The major use of starch acetates have been in the study of the stmctures of amylose and amylopectin after acid hydrolysis. Acetylation of granular starch in aqueous suspension by acetic anhydride at pH 10-11 is used to produce low d.s. starch acetates that are primarily used for the stabilization of their viscosity and for their water-soluble clarity. The acetylation decreases the hydrophilic character and increases the hydrophobic character of starch. The major uses of starch acetates is in the paper industry for surface sizing to give improved print quality, uniform porosity, surface strength, and resistance to various solvents [161]. 

Here U, is an internal energy of the skeleton, S, -entropy of solid phase, <50 - external stream of heat, SQ >0 - uncompensated heat, JA " -elementary work of the internal surface strength. 

Finished surfaces Strength orientation Random One Random Random One One Orientation of ply Two Depends on wind Two Two Directional... 

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