Conservation of Historic Stone Buildings and Monuments (1982) / Chapter Skim
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The Suitability of Polymer Composites as Protective Materials
The Suitability of Polymer Composites as Protective Materials
Pages 312-321
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From page 312... ...
The realization that many historic structures are slowly deteriorating under centuries of exposure to atmospheric conditions, a deterioration often accelerated by the gaseous and particulate pollutants so common in today's urban environment, has led to the development of many novel techniques of preservation. Among those techniques is the application of synthetic organic monoAnthony T
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From page 313... ...
A few of the characteristics that determine whether the treatment will be helpful or harmful are the solids content of the composite, the adhesion between the resin matrix and the filler, the adhesion between the polymeric composite and the stone substrate, the matching of physical properties between the polymer composite and the stone, and especially the choice of resin matrix. POLYMER COMPOSITES AS PATCHING MATERIALS A low-viscosity polyester or epoxy prepolymer can be filled with crushed and graded stone particles and a pigment to produce an adhesive patching compound.
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From page 314... ...
Cal CO .q .q O O P
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From page 315... ...
315 - si—0 - Si—O ~ SiR—CH—CH2 - si-o 'Cal - - Si_O > Si—R—CH—CH2 Ol + Resin Matrix + R NH2 Proper choice of a coupling agent is essential to the development of maximum physical properties and, perhaps more importantly, to longterm stability in the presence of moisture or soluble gases, such as sulfur dioxide. In the absence of good adhesion between the phases, thermal stresses will lead to debonding of the imbedded.
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From page 316... ...
Q Substrate FIGURE 2 With poor adhesion between phases in a silicate-resin patching material, thermal stresses will lead to debonding of imbedded particles and microcavitation of matenals. Water and gases can then collect at interracial voids and cause accelerated degradation of inorganic phase.
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From page 317... ...
Some polyesters, for example, have relatively Tow resistance to atmospheric humidity, while others are highly resistant. Filled Pore 1 Polymer Coating Stone Substrate Coated Pore FIGURE 4 Bonding strengthened by forcing polymer into pores.
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From page 318... ...
The bisphenol-A-based polyesters are commonly used and are highly resistant to a wide variety of harsh environmental conditions. TABLE 3 Some Gas Permeation Values Through Polymer Films at 30° C P x 10~° (cc (STp)
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From page 319... ...
Other commercially available formulations are simply too numerous to mention. It is possible to formulate epoxies with softening points ranging from 50° C to 200° C, with water;solubilities ranging from less than 0.1 percent to more than 5 percent, with gas-transmission rates varying by orders of magnitude, and with mechanical properties ranging from high ductility and impact resistance to extreme brittleness.
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From page 320... ...
Thus, it may be difficult to make a silicone penetrate the surface pores, which would~ result in shadow impregnation, clogging of pores, and a surface fiLn that could be subject to peeling. Some of the most satisfactory epoxy prepolymers also have very high viscosities, which decrease the depth of penetration.
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From page 321... ...
Bonding Organic Polymers to Glass by Silane Coupling Agents. 1h Fundamental Aspects of Fiber Reinforced Plastic Composites, R.T.
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