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The microstructure-property relationships in multicomponent ethylene1-alkene copolymers with different branching in the microstructures are demonstrated. The metallocene catalyzed linear low density polyethylene (mLLDPE), was miscible with both autoclave grade low density polyethylene (LDPE-A) and/or tubular grade low density polyethylene (LDPE-T). For these multicomponent systems, the rheological response was distinctly differentiating and sensitive to the microstructure of LDPE, at higher shear regimes. The thicker lamellae of LDPE-T and/or LDPE-A might co-crystallize if there is a high density polyethylene-like fraction present in the mLLDPE. Even though the macro parameters like density and melt index (MI) of the investigated multicomponent systems are comparable, the subtle differences in the microstructure manifested by type and distribution of comonomer and/or branching affected the sealing performance. Both high comonomer content and comonomer distribution in the mLLDPE matrix affording a higher fraction of material melting below 120[degrees]C were found to be critical for the heat sealing. The fraction of material melting at lower temperatures, attributed to the tertiary branches present in the hyper-branched microstructure of LDPE-A, participate in the sealing process, and lower the sealing temperature. It was evident that mLLDPE with asymmetric distribution of lamellae is more sensitive to the microstructure of the LDPE used. KEYWORDS autoclave reactor, heat sealing, polyethylene microstructure, recycling, thermo-rheological behavior, tubular reactor, 1 | INTRODUCTION Linear low density polyethylene (LLDPE) is often blended with minor amounts of low density polyethylene (LDPE) for blown film applications for better processability and optical properties. [1] [...]

Microinjection molding is one of the most efficient processes for wide-scale production of thermoplastic polymer microparts. The injection molding process with a cold mold suffers from drawbacks, that is, the premature solidification, caused by the small thickness and large temperature difference between the surface of the mold and the incoming polymer. In this work, an original and versatile system to dynamically control the local temperature of the cavity surfaces in microinjection molding was developed. The system was used to investigate the effects of rapid variations of the temperature of a 200 [micro]m thick cavity on the reachable flow length and study the morphology of microinjection molded parts of polyjlactic acid). For the rapid mold temperature control, electrical resistive thin components are located very near the surface of the impression to change the temperature by some tens of degrees per second. This study also demonstrates that the system is able to influence the final morphology of the part with a semicrystalline thermoplastic material. Changing the annealing time and temperature, the effects on the morphology of the part, in the mold and immediately after the injection, were investigated by microscopy analysis and X-ray diffraction., INTRODUCTION The microinjection molding ([mu]IM) process is a commonly used technology for manufacturing components with dimensions or features in the micrometer scale. Because of the small part thickness, the process [...]

Foam injection molding is a process by which complex, thick parts with a cellular core and a compact solid skin can be manufactured. The addition of a physical blowing agent under high pressure allows the decrease of the viscosity and the glass transition temperature of the gas/ polymer melt. These features of the foam injection molding are very beneficial for biodegradable polymers, in which the processability window is very narrow. In this study, morphology, rheological, and mechanical properties of parts with a complex shape, obtained by foam injection molding, were analyzed. In particular, two commercial grades of poly(lactic acid) having different rheological behavior were adopted to obtain foamed parts by injection molding process with nitrogen as a physical blowing agent. For both resins, the effect of the mold opening on morphology and mechanical properties was assessed., INTRODUCTION Foam injection molding is a very advantageous process to make parts having better dimensional stability with less material and a faster production cycle with respect to the conventional injection [...]

Although Poly(lactic acid) (PLA) possesses many desirable properties, above all biodegradability, its heat deflection temperature is too low for many desirable applications. Similarly, to any other polymers, also for PLA the physical and mechanical properties in the solid state depend on the morphology and crystallinity degree, which in their turn are determined by the thermomechanical history experienced during solidification. A large crystallinity degree is highly desirable to increase the heat resistance of PLA but is rather difficult to reach during injection molding due to the very slow crystallization kinetics of this material. In this work, the crystallization kinetics of an injection molded PLA grade was assessed in function of the thermal history by using calorimetric analysis. The cold crystallization kinetics (starting from the amorphous glassy sample) turned out to be faster than melt crystallization kinetics. Following the indications gained from crystallization kinetics, some samples were injection molded imposing different thermal histories. The effect of molding conditions on crystallinity was determined. This finding was adopted to develop a post-molding stage which allows obtaining crystalline samples in times much shorter (of a factor about two) with respect to samples injection molded in a hot mold kept at temperatures close to the maximum crystallization rate., INTRODUCTION Physical, thermal, and mechanical properties of thermoplastic polymers are strongly dependent on the crystalline structure and morphology. For this reason, crystallization is a major research interest in the field [...]