Density stiffness

Poly(ethylene-i (9-vinyl alcohol) is made by saponification of ethylene—vinyl acetate copolymers. The properties of these materials depend on the amount of vinyl alcohol present in the copolymer. High vinyl alcohol content results in more hydrophilic materials possessing higher densities, stiffness, and moduh. They are used commercially as barrier resins for packaging. Important producers include Du Pont and EVALCA (74) (see Barrier polymers). 

From a brief consideration of the properties of the above three polymers it will be realised that there are substantial differences between the crystallisation of simple molecules such as water and copper sulphate and of polymers such as polyethylene. The lack of rigidity, for example, of polyethylene indicates a much lower degree of crystallinity than in the simple molecules. In spite of this the presence of crystalline regions in a polymer has large effects on such properties as density, stiffness and clarity. 

Naturally, fibers and whiskers are of little use unless they are bonded together to take the form of a structural element that can carry loads. The binder material is usually called a matrix (not to be confused with the mathematical concept of a matrix). The purpose of the matrix is manifold support of the fibers or whiskers, protection of the fibers or whiskers, stress transfer between broken fibers or whiskers, etc. Typically, the matrix is of considerably lower density, stiffness, and strength than the fibers or whiskers. However, the combination of fibers or whiskers and a matrix can have very high strength and stiffness, yet still have low density. Matrix materials can be polymers, metals, ceramics, or carbon. The cost of each matrix escalates in that order as does the temperature resistance. 

This procedure causes reduced fusion defects and increases the crystallinity, density, stiffness, hardness, and yield strength. Further, it results in an increased resistance to creep, oxidation and fatigue. 

When a resin or heavy filler is replaced with the microspheres, most physical properties are reduced, based on constant volume (lower density). Stiffness is reduced, due to the resilient characteristics. Strength/weight ratio, fatigue, stress and resilience can offer useful product enhancement, with relatively small additions. 

Property modulus strength Elongation Izod, notched (Density) stiffness strength ... 

Once the fill is placed, testing can be performed to verify the initial assumptions. If necessary compaction needs to be performed in order to obtain the required density/stiffness. A CPT is the most common tool to test the fill mass over its entire thickness, however the derivation of stiffness is indirect and may require calibration (for instance Section 9.1.5.1, Cone Penetration and Standard Penetration testing in carbonate sands and see Appendix C). Additionally, with a seismic CPT, also Gq can be measured. 

Degree of crystallinity of semicrystalline polymers—on density, stiffness, strength, and ductility (Sections 14.11 and 15.8). 

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