2014, Thanomchat, Sarit, Srikulkit, Kawee, Suksut, Buncha, Schlarb, Alois Karl

Microfibrillated cellulose (MFC) was prepared by controlling the re-precipitation of cellulose prepared in the mixture form of NaOH/Urea solubilized microcrystalline cellulose (MCC) and starch. The cellulose re-precipitation was carried-out in an HCl bath, resulting in a MFC form having relatively lower crystallinity than MCC. The XRD pattern of MFC indicated the partially crystalline structure arising from the imperfect orientation of a cellulose chain obstructed by a starch molecule in the precipitation step. Interestingly, the MFC morphology exhibited a web-like structure with a diameter in the range of 10-20 nm. The water retention value of MFC was extraordinarily high due to its extremely small diameter having high surface area. Further, surface silanization of MFC with organosilane was carried out. Then, the modified MFC was melt-mixed with polypropylene (PP) matrix via a simple melt mixing technique. The morphology and crystallization of the PP/MFC composites were measured. The morphology of organosilane treated MFC exhibited agglomeration of 10 microns in diameter with layered structures arising from the packing of microfibrils. The FTIR spectra showed hydrophobic characteristics of treated MFC observed by the disappearance of original cellulose hydroxyl group and bound water. The crystallinity of treated MFC increased when compared to the untreated MFC, indicating that cellulose chains of unmodified MFC underwent re-orientation occurring in the modification step due to its high crystallinity characteristic. For the PP/MFC-composite containing MFC loading, faster crystallization and higher spherulite growth rate, in case of higher MFC loading, were observed. In addition, the spherulite size decreased with an increase in the crystallization temperature. However, the degree of crystallinity was fairly independent on the MFC-loading. Therefore it can be concluded that the addition of MFC might enable shorter cycle times, resulting in cheaper processing cost in a view point of polymer processing.

2015, Nomai, Jiraporn, Suksut, Buncha, Schlarb, Alois K

In this study, a poly(lactic acid) (PLA) with various titanium dioxide (TiO2) nanoparticles loading were prepared by a manual laboratory mixing method. The effect of TiO2 nanoparticles on the non-isothermal and the isothermal crystallization behavior of PLA was investigated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The presence of TiO2 nanoparticles decreased the spherulite growth rate of PLA, whereas it initiated faster crystallization through the heterogeneous nucleation process as observed by optical microscopy. The results of DSC analyzes confirmed that the TiO2 nanoparticles act as an efficient nucleating agent for PLA crystallization. The cold crystallization temperature and crystallization half-time of PLA decreased, while the degree of crystallinity of PLA increased in relation to increases of TiO2 nanoparticles.

2015, Schlarb, Alois K., Lin, Leyu, Suwitaningsih, Dwi N., Suksut, Buncha

Although the research and development of nanocomposites for almost a decade focused on structural properties, these properties remained until today far below expectations, which were forecast at the beginning of the new millennium. However, even if it is well known that the processing history has a major impact on the structure and properties of final components, this aspect was not subject of intensive research in the past. The talk focuses on the role of the manufacturing sequence on the morphology and properties of polypropylene based nanocomposites. In general it can be stated that the incorporation of nano-sized TiO2-fillers improves the some mechanical properties of the resulting nanocomposites as long as the production enables a good dispersion and distribution of the nanofiller agglomerates. However, with increasing filler loading, the morphology of injection molded parts changes: The size of the spherulites and the degree of crystallinity decreases while the crystallization/solidification proceeds faster. Simultaneously a slight improvement in the mechanical performance up to a certain filler loading can be found. However, improved mechanical properties of the nanocomposites in the final component cannot be exploited if its production in a subsequent welding step is required. The reason for the decrease in the mechanical properties is the decrease in the viscosity by the addition of the fillers, and thereby caused extreme flow processes and subsequent orientation of the fillers as well as the weakening of the filler/matrix-interphase in the welding zone. In summary, it can be observed that nanocomposites increasingly offer great opportunities for applications where single-component materials reach their limits. The key to success is the processing. Therefore it is of crucial importance that the total manufacturing history is understood and controlled. Only then it is possible to sustainably exploit the potential of polymer nanocomposites in the application.