This study presents the applicability of different types (exothermic and endothermic) of chemical blowing agents (CBAs) in the case of poly(lactic acid) (PLA). The amount of foaming agent is a fixed 2 wt%. We used a twin-screw extruder and added the individual components in the form of dry mixture through the hopper of the extruder. We characterized the PLA matrix and the chemical blowing agents with different testing methods. In case of the produced foams we carried out morphological and mechanical tests and used scanning electron microscopy to examine cell structure. We showed that PLA can be successfully foamed with the use of chemical blowing agents. The best results were achieved with an exothermic CBA and with PLA type 8052D. The cell population density of PLA foams produced this way was 4.82 × 105 cells/cm3, their expansion was 2.36, their density 0.53 g/cm3 and their void fraction was 57.61%.

This study presents the investigation of different content of thermally expandable microsphere (EMS) type of a physical blowing agent added to polylactic acid (PLA). The effects of the different doses of EMS, processing temperatures, and d-lactide content of the polylactic acid were analyzed for foam properties and structures. We characterized the different PLAs and the physical blowing agent with different testing methods (gel permeation chromatography, rotational rheometry, isothermal thermogravimetric analysis, and thermomechanical analysis). The amounts of the foaming agent were 0.5, 1, 2, 4, 8 wt%, and processing temperatures were 190 °C, 210 °C, and 230 °C. The foam structures were produced by twin-screw extrusion. We used scanning electron microscopy to examine the cell structure of the foams produced, and carried out morphological and mechanical tests as well. The result of extrusion foaming of PLA using different amounts of EMS shows that an exponentially decreasing tendency of density reduction can be achieved, described by the following equation, ρ(x ) = 1.062 · e − x 7.038 + 0.03 (R2 = 0.947) at 190 °C. With increasing processing temperature, density decreases at a lower rate, due to the effect that the microspheres are unable to hold the pentane gas within the polymer shell structure. The d-lactide content of the PLAs does not have a significant effect on the density of the produced foam structures.

No abstract

No abstract

This study presents the comparative study of two different accelerated aging methods of poly(D-,L-lactide acid) (PLA). One is the well-known and widely used accelerated weathering chamber. The other procedure is photodegradation with a homogenized laser beam, which has not been used for the artificial aging of biopolymers so far. The film sample was artificially aged with a xenon test chamber for 200 hours, with an acceleration factor of approximately 7:1. We also performed a comparative artificial aging test using a krypton-fluoride (KrF) excimer laser in a way that the amount of energy transferred by the laser is the same as the energy transferred by the xenon lamp; the acceleration factor of the laser is higher than 42000:1. The resulting two types of photodegraded film products were compared and broadly characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), gel permeation chromatography (GPC) and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR); the goal was to create comparison and possible conformity between the two methods to achieve higher acceleration factor for accelerated aging.

No abstract

No abstract

This paper presents the characterization of poly(lactic acid)-based chemically foamed foam structures. We used extrusion grade, high molecular weight poly(lactic acid) as matrix material and azodicarbonamide as foaming agent. The resulting foams were characterized by foam density, cell population density, scanning electron microscopy, and based on the fracture surface of the foam cross-section, we calculated cell size distribution. The obtained distributions were fitted with the use of log-normal distribution in each case. We presented the effect of chemical blowing agent content (0.5 wt%, 1 wt%, 2 wt%, 4 wt% and 8 wt%) on the PLA-based foam structure and the effect of processing temperature (190 °C, 210 °C and 230 °C) on cell size distribution.