Semicrystalline Solids

Poly(ethylene oxide) (usually abbreviated to PEO) has been the most intensively studied host polymer for polymer electrolytes and it serves as a prototype for the structural features in most of the more advanced polymer electrolyte hosts. It consists of —O—CHj—CHj— repeat units and occurs as a semicrystalline solid. The relative orientations of groups... 

Polymers can exist as liquids, as elastomers or as solids but can be transferred into the gaseous state only under very special conditions as are realized in, for example, MALDI mass spectrometry. This is because their molecular weight is so high that thermal degradation sets in before they start to evaporate. Only a few polymers are technically applied in the liquid state (silicon oils, specidty rubbers) but most polymers are applied either as elastomers, or as rigid amorphous or semicrystalline solids. 

PE crystal, the penetration length of the mechanical excitation into the lamella was found to be about 5 nm. As a result, if the tie molecule ends in the lamella or continues and ends in an amorphous region, the axial forces it can be exposed to are very small. Such a tie molecule contributes very little to the strength of a semicrystalline solid. 

Nylon-6 [25038-54-4] was first made in 1899 by heating 6-aminohexanoic acid (143), but its commercially feasible synthesis from caprolactam was discovered by Paul Schlack at I. G. Farbenindustrie in 1938. Like nylon-6,6, it is a tough, white translucent, semicrystalline solid, but melts at a lower temperature (7, = 230° C. The physical properties and primary producers of nylon-6 are listed in Tables 9 and 10, respectively. 

The aqueous solution was concentrated in vacuo to a volume of 4 ml. Addition of acetone (40 ml) gave an oily precipitate which after decanting and addition of fresh acetone gave 900.0 mg of a semicrystalline solid which contained 50% of the theoretical amount of 3-aminoadamantyl-l-penicillin. 

Plastics are either truly homogeneous, amorphous solids or heterogeneous, semicrystalline solids. There are no purely crystalline plastics since so-called crystalline materials also contain different amounts of amorphous material semicrystalline is technically more accurate. Various methods of defining and evaluating plastics are used such as their molecular weight distribution (MWD). A narrow MWD enhances the performance of plastic products. MWD effects melt-flow rates. 

The term elastomer is often used interchangeably with the term rubber. Elastomers (or rubbers) are amorphous polymers. Their normal-use temperatures are above their glass transition temperatures, so considerable molecular segmental motion is possible. Hard plastics normally either exist below their glass transition temperatures, or they are semicrystalline solids at room temperature. 

A full mechanical characterization of any material for deformations in the linear regime is given by the stiffness or compliance matrix, respectively. For the interlamellar domain at P = 1 atm and T = 435 K, we extracted exactly these matrices, from which Young s moduli and shear moduli were determined. According to the simulations, the bulk modulus of the interlamellar domain lies between between the experimental values reported for a purely amorphous melt and the semicrystalline solid. 

Polypropylene (PP) is a thermoplastic material that is produced by polymerizing propylene molecules, which are the monomer units, into very long polymer molecules or chains. There are a number of different ways to link the monomers together, but PP as a commercially used material in its most widely used form is made with catalysts that produce crystallizable polymer chains. These give rise to a product that is a semicrystalline solid with good physical, mechanical, and thermal properties. Another form of PP, produced in much lower volumes as a byproduct of semicrystalline PP production and having very poor mechanical and thermal properties, is a soft, tacky material used in adhesives, sealants, and caulk products. The above two products are often referred to as isotactic (crystallizable) PP (i-PP) and atactic (noncrystallizable) PP (a-PP), respectively. 

The following notation is used in this chapter. Polypropylene containing only propylene monomer in the semicrystalline solid form is referred to as homopolymer PP (HPP), and we use this to mean the i-PP form. Polypropylene containing ethylene as a comonomer in the PP chains at levels in about the 1-8% range is referred to as random copolymer (RCP). HPP containing a comixed RCP phase that has an ethylene content of 45-65% is referred to as an impact copolymer (ICP). Each of these product types is described below in more detail. 

Zhu Q, Taylor LS, Harris MT (2010) Evaluation of the microstmcture of semicrystalline solid dispersions. Mol Pharm 7(4) 1291-1300... 

Separate correlations exist for (1) amorphous solid, (2) semicrystalline solid, and (3) molten polymers. For example, a generalized correlation [4] for solid amorphous polymers is given in Fig. 4-2. This requires the Tg for the polymer and the thermal conductivity at Tg (this can be bypassed if one thermal conductivity is known at a given temperature). Hence, Fig. 4-2 requires specific data before it can be used. 

Semicrystalline solid Milk carton adhesives and coatings... 

Unfortunately, any attempt to predict the long-term stability of polyethylene based on an Arrhenius plot of high-temperature oxidative induction times measured above the melting point fails when projected to lower temperatures where polyethylene is a semicrystalline solid (Bair 1973 Chan et al. 1978). The reasons for this nonlinear behavior appear to be associated with complex chemical and physical interactions that behave differently in the solid state than in the melt. 

Blown film extrusion is the most common method to fabricate polyethylene film. The process involves extruding molten polyethylene through a circular die and then inflating the interior of the molten polyethylene as it exits the die to form a bubble. The die thickness is about 20-100 times thicker than the final film thickness, so that the molten polyethylene is stretched during the time that the molten polyethylene exits the die and before the time the molten polyethylene cools to a solid. Important aspects of this process are a uniform film thickness, the time it takes to cool the molten, amorphous polyethylene to a semicrystalline solid and the molecular structure of the polyethylene used to fabricate the film. During this cooling process the volume of the polyethylene shrinks as the solid material has a higher density than the molten polyethylene. 

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