The polymerization of cyclic butylene terephthalate oligomers (CBT) were studied in presence (in 5 wt.%) and absence of an organoclay (Cloisite® 30B) by modulated DSC (MDSC). The organoclay containing samples were produced by dry and melt blending, respectively. The first heating, causing the polymerization of the CBT catalyzed by an organotin compound, was followed by cooling prior to the second heating. The MDSC scans covered the temperature interval between 0 and 260°C. The aim of this protocol was to study the crystallization and melting behavior of the resulting polybutylene terephthalate (pCBT) and its organoclay modified nanocomposites. It was found that the thermal behaviors of the polymerizing and polymerized CBT (pCBT) were strongly affected by the sample preparation. The organoclay suppressed the crystallization of the pCBT produced during the first heating. However, results from the second heating suggest that more perfect crystallites were formed in the organoclay modified pCBT variants. The organoclay also affected the conversion and mean molecular mass of the resulting pCBT which were slightly lower than those of the plain pCBT polymerized under identical conditions.
Polyketone was prepared by the copolymerization of carbon monoxide (CO) and styrene (ST) catalyzed by o-phenylenediamine resin-supported palladium acetate. Effects of each catalytic system component such as 2,2’-bipyridine, 1,4-quinone and p-toluene-sulphonate on the copolymerization were investigated. The resin-supported catalyst and the copolymerization product were characterized by infrared spectroscopy (IR), differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM). Results indicated that the resin-supported catalyst has excellent catalytic property. Furthermore, partial catalytic activity was maintained after the catalyst was used for five times.
Polyamide (PA6) nanocomposites containing 4wt% organo-montmorillonite (OMMT) were melt-compounded followed by injection molding. The mechanical properties of the PA6/OMMT nanocomposites were studied through tensile and flexural tests. The rheological behaviour of the nanocomposites was determined by plate/plate rheological measurements. Attempts were made to trace the rheological parameters that reliably reflect the observed changes in the clay dispersion. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used to characterize the exfoliation and dispersion of the OMMT in the PA6 matrix. The thermal properties of PA6/OMMT nanocomposite were characterized by Dynamic Mechanical Thermal Analysis (DMTA). The tensile modulus and strength of the PA6 was increased in the presence of OMMT. The flexural strength of PA6/OMMT was approximately doubled compared to the tensile strength value. The significant enhancement of both tensile and flexural strength was attributed to the delaminated clay formation. XRD and AFM results revealed the formation of PA6 nanocomposites as the OMMT was successfully exfoliated.
A new method based on variable transformation is proposed for the estimation of the constant strain rate tensile test by using a previously introduced concept of viscoelastic response given to the real relaxation stimulus. The time range of the “good” fitting is 2.5 to 3 times larger than the best results achieved using linear viscoelastic approximations. The theoretical background of the method was elucidated as well.
Although high density polyethylene (HDPE) is one of the most widely used industrial polymers, its application compared to its potential has been limited because of its low dimensional stability particularly at high temperature. Dilatometry test is considered as a method for examining thermal dimensional stability (TDS) of the material. In spite of the importance of simulation of TDS of HDPE during dilatometry test it has not been paid attention by other investigators. Thus the main goal of this research is concentrated on simulation of TDS of HDPE. Also it has been tried to validate the simulation results and practical experiments. For this purpose the standard dilatometry test was done on the HDPE specimens. Secant coefficient of linear thermal expansion was computed from the test. Then by considering boundary conditions and material properties, dilatometry test has been simulated at different heating rates and the thermal strain versus temperature was calculated. The results showed that the simulation results and practical experiments were very close together.
Low-molecular-weight PA6 (LMW-PA6)/hydrotalcite intercalated nanocomposites were prepared via insitu polymerization in the presence of organo-hydrotalcite with alanine as an initiator at 150°C.The results indicated that alanine in the interlayer gallery of hydrotalcite doesn't change the interlayer distance of hydrotalcite, while it can initiate the polymerization of ε-caprolactam. There exsists γ crystalloid of LMW-PA6 in LMW-PA6/hydrotalcite intercalated nanocomposites. The molecular weight distribution of LMW-PA6 in the intercalated nanocomposites have two peaks and the added amounts of organo-hydrotalcite hardly influence molecular weight of LMW-PA6.
The epoxy/glass fiber/organo-montmorillonite (OMMT) nanocomposites were prepared by hand lay up method. In the previous work, the flexural and morphological properties of the epoxy/glass fiber/OMMT were studied. In this work, the epoxy nanocomposites were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and water absorption tests. The exfoliation of OMMT in epoxy/glass fiber nanocomposites was detected by XRD. DSC results showed that the glass transition temperature (Tg) of epoxy was increased slightly in the presence of OMMT. Water uptake of epoxy was reduced by the addition of glass fiber and OMMT. The decrease of water absorption in epoxy is attributed to the increasing of tortuosity path for water penetration in the epoxy composites by the hybrid of glass fiber and OMMT.
The effect of basalt fibers, produced by the Junkers technology and used as reinforcement in polymer composites, was modeled on the properties of composites, adapting the statistical fiber mat model of Poisson type. The random distribution was approximated by so-called effective spheres that act as defect sites in composites, reducing their strength. The role of fiber heads in strength reduction and the corresponding failure modes were analyzed theoretically using a model and by experiments performed on specimens containing a single fiber head located at different distances from the crack initiation. The applicability of the model was proven both experimentally and by finite element analysis. Based on all these investigations, the effective cross section reduction, and hence the strength reduction (predicted by the model) caused by the presence of fiber heads was proven.