Crystallization behavior of poly(lactic acid)/titanium dioxide nanocomposites

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

Morphology and crystallization of polypropylene/microfibrillated cellulose composites

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

Competitive effect of calcium lactate and epoxidized soil bean oil on crystallization kinetics of polypropylene

The effect of calcium lactate (CL) and epoxidized soil bean (ESO) on the crystallization kinetics of polypropylene (PP) was investigated by using polarized optical microscope (POM) and differential scanning calorimetry (DSC). The experiments were performed under both non-isothermal and isothermal conditions. The development of spherulitic microstructure and crystallization kinetics were influenced by both CL and ESO. CL was an efficient nucleating agent for the crystallization of PP. The addition of CL facilitated faster spherulite growth and crystallization rate, while reduced the spherulite size. An opposite performance was discovered with the incorporation of ESO. Nucleation effect of CL on the PP crystallization was less effective with the presence of ESO. Compared with PP/CL, PP/CL/ESO provided a large spherulite size, slow spherulite growth, and a low crystallization rate. This is attributed to the ESO inhibited the nucleation site of CL. However, the degree of crystallinity and the Avrami exponents remained unchanged with the inclusion of both CL and ESO

Morphology and Morphology Formation of Injection Molded PP-based Nanocomposites

The mechanical properties of semi-crystalline polymers depend extremely on their morphology, which is dependent on the crystallization during processing. The aim of this research is to determine the effect of various nanoparticles on morphology formation and tensile mechanical properties of polypropylene under conditions relevant in polymer processing and to contribute ultimately to the understanding of this influence. Based on the thermal analyses of samples during fast cooling, it is found that the presence of nanoparticle enhances the overall crystallization process of PP. The results suggest that an increase of the nucleation density/rate is a dominant process that controls the crystallization process of PP in this work, which can help to reduce the cycle time in the injection process. Moreover, the analysis of melting behaviors obtained after each undercooling reveals that crystal perfection increases significantly with the incorporation of TiO2 nanoparticles, while it is not influenced by the SiO2 nanoparticles. This work also comprises an analysis of the influence of nanoparticles on the microstructure of injection-molded parts. The results clearly show multi-layers along the wall thickness. The spherulite size and the degree of crystallinity continuously decrease from the center to the edge. Generally both the spherulite size and the degree of crystallinity decrease with higher the SiO2 loading. In contrast, an increase in the degree of crystallinity with an increasing TiO2 nanoparticle loading was detected. The tensile properties exhibit a tendency to increase in the tensile strength as the core is reached. The tensile strength decreases with the addition of nanoparticles, while the elongation at break of nanoparticle-filled PP decreases from the skin to the core. With increasing TiO2 loading, the elongation at break decreases

Morphology and Morphology Formation of Injection Molded PP-based Nanocomposites

The mechanical properties of semi-crystalline polymers depend extremely on their morphology, which is dependent on the crystallization during processing. The aim of this research is to determine the effect of various nanoparticles on morphology formation and tensile mechanical properties of polypropylene under conditions relevant in polymer processing and to contribute ultimately to the understanding of this influence. Based on the thermal analyses of samples during fast cooling, it is found that the presence of nanoparticle enhances the overall crystallization process of PP. The results suggest that an increase of the nucleation density/rate is a dominant process that controls the crystallization process of PP in this work, which can help to reduce the cycle time in the injection process. Moreover, the analysis of melting behaviors obtained after each undercooling reveals that crystal perfection increases significantly with the incorporation of TiO2 nanoparticles, while it is not influenced by the SiO2 nanoparticles. This work also comprises an analysis of the influence of nanoparticles on the microstructure of injection-molded parts. The results clearly show multi-layers along the wall thickness. The spherulite size and the degree of crystallinity continuously decrease from the center to the edge. Generally both the spherulite size and the degree of crystallinity decrease with higher the SiO2 loading. In contrast, an increase in the degree of crystallinity with an increasing TiO2 nanoparticle loading was detected. The tensile properties exhibit a tendency to increase in the tensile strength as the core is reached. The tensile strength decreases with the addition of nanoparticles, while the elongation at break of nanoparticle-filled PP decreases from the skin to the core. With increasing TiO2 loading, the elongation at break decreases

Image analytical determination of the spherulite growth in polypropylene composites

Measuring the growth of spherulites in semi-crystalline thermoplastics helps to control and optimize industrial manufacturing processes of these materials. The growth can be observed in cross polarized images, taken at several time steps. The diameters of the spherulites are however measured manually in each step. Here, two approaches for replacing this tedious and time consuming method by automatic image analytic measurements are introduced. The first approach segments spherulites by finding salient 5x5 pixel patches in each time frame. Combining the information from all time frames into a 3D image yields the spherulites by a maximal flow graph cut in 3D. The growth is then measured by homography measurement. The second approach is closer to the manual method. Based on the Hough transform, spherulites are identified by their circular outline. The growth is then measured by comparing the radia of the least moving circles. The pros and cons of these methods are discussed based on synthetic image data as well as by comparison with manually measured growth rates

Process-morphology-property-relationships of titania-filled polypropylene nanocomposites

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