Crystallinity by weight

Another more convenient method of determining the crystallinity is to measure the heat of fusion, AHf, of a sample. This leads us to use the weight fraction of the crystalline phase rather than the volume fraction as above. The crystallinity by weight, 0, can be determined from the heat of fusion, AHf, by ... 

The density of a crystalline polymer will be greater than an amorphous one of the same material and molecnlar weight because the chains are more closely packed together for the crystalline strncture. The degree of crystallinity by weight may be determined from accnrate density measurements, according to... 

Many of flie pnoperties of FTFE are not constant but change systematically with crytalline content, molecular weight, void content, temperature, pressure, or some other independent variable. Where available, fliese inter-relationships are shown even fliough they are usually empirical rather than fundamental. Throughout the table, %C indieates percent crystallinity by weight. 

The lasing medium in the titanium-sapphire laser is crystalline sapphire (AI2O3) with about 0.1 per cent by weight of Ti203. The titanium is present as Ti and it is between energy levels of this ion that lasing occurs. 

It must be kept in mind that mechanical properties are influenced by factors other than the degree of crystallinity (molecular weight, in particular). 

Aluminum chloride hexahydrate is available ia a 28% by weight (32° Be ) aqueous solution shipped ia glass carboys, tank cars, or tmcks. Crystalline hexahydrate is shipped ia glass containers or plastic-lined dmms. In 1980, 5200 metric tons of aluminum chloride hexahydrate on a 100% AlCl basis was produced ia the United States (10). 

Cellulose is the main component of the wood cell wall, typically 40—50% by weight of the dry wood. Pure cellulose is a polymer of glucose residues joined by 1,4-P-glucosidic bonds. The degree of polymerization (DP) is variable and may range from 700 to 10,000 DP or more. Wood cellulose is more resistant to dilute acid hydrolysis than hemiceUulose. X-ray diffraction indicates a partial crystalline stmcture for wood cellulose. The crystalline regions are more difficult to hydrolyze than the amorphous regions because removal of the easily hydrolyzed material has Htde effect on the diffraction pattern. 

The cymidin is now sulphonated, 100 parts by weight of cymidin being slowly added to 69 parts by weight of sulphuric acid (sp. gr. 1 84), contained in a shallow dish, and the solid crystalline mass of cymidin sulphate thus obtai ed is then converted into cymidin sulphonic acid by an identical method to that tised in the so-called baking process for the preparation of stilphanilic acid from aniline sulphate. 

A solution of 10.0 grams of purified S-methyl ether of 2-thio-5-fluorouracil, MP 230° to 237°C, in 150 ml of concentrated aqueous hydrochloric acid (containing approximately 37% by weight HCI) was refluxed under nitrogen for 4 hours. The reaction mixture was then evaporated in vacuo. The crystalline brownish residue was recrystallized from water. The resulting recrystallized product was further purified by sublimation in vacuo at 190° to 200°C (bath temperature)/0.1 mm pressure. There was obtained 5-fluorouracil, in the form of colorless or pinkish-tan crystals, MP 282° to 283°C (with decomposition). 

Increasing the molecular weight of polyester (or polyether) or changing its chemical composition could lower the Tg of the TPU and decrease the crystallinity of the polymer. For example, a TPU composed of poly(S-lactone), MDI, and 1,4-butanediol was found to have the lowest degree of crystallinity and, therefore, the best compatibility with PVC when the hard segment in it is 36% by weight [10]. 

The copolymerisation of ethylene with vinyl acetate (VA) is another method by which the crystallinity of polyethylene can be reduced and a rubbery polymer obtained. The final properties of the copolymer depend on the VA content at a VA level of 50% the copolymer is entirely amorphous, and elastomeric grades generally contain 40-60% VA by weight. The oil resistance of the copolymer is also dependent on the VA content in general, however, this lies between that of SBR and polychloroprene. It is swollen by most organic solvents and not resistant to animal and vegetable oils, but has some resistance to weak acids and alkalis at ambient temperature. 

In this study five cellulose samples of different crystallinities (10, 41, 63, 67, and 742) were treated to 10% by weight with H PO, H3BO3, and AlClo i O. These treated samples and untreated (control) samples were isothermally pyrolyzed under N2 at selected temperatures and the TGA data analyzed by four methods (0—, 1st-, and 2nd-order and Wilkinson s approximation) to obtain rates of mass loss. From these rates, activation energy (Efl), activation entropy (AS+) and enthalpy (AH+) values were obtained. Efl was also determined by the integral conversion method. 

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