No abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.

Post-curing is intended to improve strength, elevate glass transition, and reduce residual stress and outgassing in thermosets. Also, experiments indicate post-curing temperatures lead to ether crosslinks and backbone dehydration. These results informed molecular dynamics methods to represent them and compare the resulting thermomechanical effects. Diglycidyl ether of bisphenol A (DGEBA)-diamino diphenyl sulfone (DDS) systems were examined. Independent variables were resin length, stoichiometry, and reaction type (i.e., amine addition, etherification, and dehydration). Etherification affected excess epoxide systems most. These were strengthened and became strain hardening. Systems which were both etherified and dehydrated were most consistent with results of post-curing experiments. Dehydration stiffened and strengthened systems with the longer resin molecules due to their intermediate hydroxyl groups for crosslinking. Changes in the concavity of functions fit to the specific volume versus temperature were used to detect thermal transitions. Etherification generally increased transition temperatures. Dehydration resulted in more transitions.

Greenwood cuttings from greenhouse-produced tamarack seedlings and 3- to 10-year-old tamarack wildlings transplanted from natural stands in north-western Ontario were rooted under mist in peat-vermiculite. Eighty-five percent of cuttings from seedlings rooted; treatment with indolebutyric acid increased number of roots per cutting, but not rooting percent. At 6 weeks after planting, rooting of cuttings from wildlings averaged 66%, and at 12 weeks, 91%. Twelve-week rooting percent of cuttings from individual ortets ranged from 12 to 100, but cuttings from the majority of ortets exhibited 100% rooting. Nearly all rooted cuttings survived overwintering outdoors and initiated normal shoot growth after forcing in mid-winter. The described propagation system is recommended for production of container stock for tamarack plantations. North. J. Appl. For. 3:91-93, Sept. 1986.