Nylon 1212 Mark - Houwink Parameter Set And Molecular Weight On The Influence Of Crystallization Behavior

By using the stepwise precipitation method, we classified nylon1212by different molecular weight. Here, Ubbelohde Viscometer, Light Scattering and Gel Permeation Chromatography (GPC) are used for the determination of all gradation’s intrinsic viscosity numbers, molecular weights and molecular weights distribution. The values of K and α in the Mark-Houwink equation were calculated. We used DSC and PLM to study the influence of molecular weight for the non-isothermal crystallization kinetics and crystalline pattern The main conclusions are as follows:1. We designed and synthesized five different categories of nylon1212with molecular weight ranged from5×103to20×103g/mol. Then, by gradual precipitation classification for each sample, intrinsic viscosity of each fraction was ascertained. We choose5categories with larger difference intrinsic viscosity, by Static Light Scattering and GPC to determine the Weight Average Molecular Weight and Molecular weight distribution. Normal distribution grading is obtained, and grading recycling rate was more than85%. The molecular weight and design molecular weight are almost the same for the category with the most content of each sample. GPC showed that the weight distribution index (Mw/Mn) is around1.4and weight distribution is narrow, meet the requirements of Mark-Houwink equation for molecular weight distribution index. A linear relation was obtained with lg|η]～lgMw, plotting. The intercept and slope show that in the studied molecular weight range, the K. value for the Mark-Houwink is7.92x10-3mL/g, and α value is0.83, Mark-Houwink formula is:[η]=7.92×10-3M0.83w2. By using the DSC in studying for non isothermal crystallization kinetics of narrow distribution nylon1212, we got:With the increase of molecular weight, the melt viscosity increased, the motion capacity of the molecular chain decreased,the crystallization rate slow down.In the non isothermal crystallization process of nylon1212of different molecular weight, the Ozama index m altered from approximately3to approximately4 Illustrated that the three-dimensional spherulite nucleation and growth for small weight molecular is heterogeneous nucleation, and homogeneous nucleation for large weight molecular.The crystallization activation energy increased with the increase of molecular weight, illustrate that the molecular weight of nylon1212has influence on the non-isothermal crystallization process, the crystallization becomes more difficult3. Nylon of different molecular weight were melted and cast to film, and isothermal crystallized at different temperatures, then observed through polarized light microscopy, results show:when crystallized at165℃, alternately dark and bright rings phenomenon along the radius direction of spherulites, showing the spherulites growth speed is fast, and lamellaes were not perfect, plus dynamic reasons and the exist of structure defects lead to the internal stress concentration, and the spherulites size is relatively large, so the phenomenon of banded spherulites were finally observed.At identical temperature, spherulites size decreased with the increase of molecular weight, which originates from the nucleation density increase corresponding to molecular weight increase. In the common effect of nucleation and growth, spherulite size of nylon1212decreases as the molecular weight increases gradually.With the increase of culture temperature, nylon1212crystal size increases correspondingly. This is due to the barrier of nucleation increases when temperature rises, nucleation density decreases, two-dimensional spherulites’ growth space were enlarged, so nylon1212of all molecular weights present a decrease of spherulite size with an increased degree of super-cooling.