Approximation of fruit skin patterns using spherical Voronoi diagrams

In nature, there are many tessellation patterns on curved surfaces that look like Voronoi diagrams. Typical examples are the patterns found on fruit skins. Verifying that a given tessellation is a Voronoi diagram will be useful for constructing mathematical models of polygonal patterns. However, the data are usually obtained as a 2D projected image, and hence it is not easy to compare it with a Voronoi diagram on a curved surfaces. We propose a framework for using a photograph of a fruit to measure the difference between the pattern on its skin and a spherical Voronoi diagram. The problem of finding the spherical Voronoi diagram that best fits the fruit skin pattern is reduced to an optimization problem. The validity of this formulation is evaluated using jackfruit and lychee. We also propose generalizations of our problem for further research.     

The effect of polylactic acid (PLA)/poly‐d‐lactide stereocomplex on the thermal and mechanical properties of various PLA/rubber blends

This study investigated the effect of polylactic acid (PLA)/poly‐d ‐lactide (PDLA) stereocomplex (ST) on the improvement of the mechanical and thermal properties of various rubber‐toughened PLAs. In this work, natural rubber (NR), synthetic polyisoprene rubber (IR), silicone rubber (SI), acrylic rubber (ACM), acrylic core–shell rubber (CSR), thermoplastic copolyester (TPE) and thermoplastic polyurethane (TPU) were chosen as the toughening agents. 5 wt% PDLA was melt‐blended with PLA to form ST crystals in the presence of 15 wt% rubber in an internal mixer at 180 °C and 50 rpm. It was found that the melting temperature of ST crystal (T_m,sc) and the impact strength of ST/rubber blends were strongly correlated with the rubber domain size. For the blends of ST with compatible rubbers (ACM, CSR, TPE and TPU), the rubber domain sizes tended to be smaller with higher T_m,sc and higher impact strength than the blends with incompatible rubbers (NR, IR and SI). However, the presence of ST crystals in PLA/incompatible rubber blends, especially the blends with NR and IR, led to a significant increase in the rubber domain size and plunges in tensile toughness and impact strength. On the other hand, the presence of these crystals in PLA/compatible blends did not change the rubber size or the impact strength significantly compared with those without ST crystals except in the case of ST/ACM, which resulted in a large increase in the impact strength. Among all rubber types, CSR provided the highest impact strength for both the PLA and ST systems. © 2019 Society of Chemical Industry     

Development of multilayer films with improved aroma barrier properties for durian packaging application

The symmetrical A/B/A structure of multilayer blown films was fabricated in this study. The immiscible low‐density polyethylene/polylactic acid (LDPE/PLA) blend was set as a core (B) layer and LDPE was used as skin (A) layers. The compositions of PLA in the core layer were varied from 20 to 50 wt%. The thickness of each layer was 10 μm (total film thickness of ~ 30 μm). In a blown film co‐extrusion process, the morphology of the fiber/ribbon‐like structures of LDPE/PLA blend was developed. Such structures had interesting effects on gas permeability and aroma barrier properties of the films. For instance, multilayer LDPE films containing 40 and 50 wt% PLA (P40 and P50) showed the reduction of oxygen permeability (PO₂) approximately 20% and 43%, respectively, compared with the neat LDPE film. A long tortuous path for gas and aroma transportation through film thickness was created from the developed ribbon‐like structures of the PLA minor phase. For durian packaging application, fresh‐cut durian of 300 g was packed in the developed multilayer films, LDPE, and HDPE (Control), stored at 4°C for 7 days. Results demonstrated that the steady‐state condition of 10% to 13% O₂ and 8% to 10% CO₂ was achieved in all packages except in the HDPE. Moreover, the P40 and P50 films exhibited an outstanding aroma barrier property for three major durian volatiles : diethyl sulfide, ethyl propanoate, and 2‐ethyl‐1‐hexanol. Overall results clearly indicated that the multilayer LDPE films containing PLA exhibited a significantly improved aroma barrier performance with optimum gas permeability desirable for modified atmosphere packaging to retain quality of fresh‐cut durian throughout the storage period.