Determination of Phase Transitions in Gutta-Percha by Differential Thermal Analysis
Pure gutta-percha was heat-treated in a differential thermal analyzer. The high melting form crystallized on cooling when gutta-percha was heated to 70 C or less. Above 74 C, crystallization into the low melting form predominated. Either polymorph can be selectively crystallized by control of the heat-treatment temperature before cooling.
Transitions in trans‐1,4‐polyisoprene
The melting transitions of both crystalline forms of trans-1,4-polyisoprene, as detected by differential thermal analysis, have been identified by attendant studies with optical microscopy and x-ray diffraction. The lower-melting (LM) form melts initially at a temperature which depends upon the crystallization temperature but which, under our experimental conditions, is between 45 and 53°C. If recrystallization is allowed to occur, the apparent final melting point, which depends upon the recrystallization temperature, is about 58°C. The initial melting point of the higher-melting (HM) form, also crystallization temperature-dependent, is upwards of 57°C. Under the most easily accessible experimental conditions, it may be obscured by the final melting of the LM-form. The apparent final melting point of the HM form is approximately 66°C. Conversion of the LM form into the HM form occurs only by fusion and crystallization. No evidence of a solid-solid transition was found. The rate of conversion is governed principally by the rate of nucleation at the conversion temperature. If fusion of the LM form is incomplete, recrystallization of the LM form takes place instead of conversion to the HM form.
Comparative Policies of Legal Provisions for Plant Closure: Strike a Balance?
The article aims to explore the extent to which and how plant closure laws strike a balance between job security and managerial prerogative and assess the practical effects of legal provisions. To achieve this aim, the forms of underlying doctrines of legal provisions, and substantial and procedural requirements are deliberately examined by cross-national (i.e. UK, Germany, and Japan) comparisons. The findings reveal that the legal provisions of the selected nations do not seek to diminish management rights to close plants down. Instead, they attempt to impose more democratic control over the liberty and mobility of capital by negotiating with and compensating the affected workers.