Wannee Chinsirikul

Nd:YAG Laser Perforation of Plastic Films for Enhanced Breathability

This study focused on investigating the Nd:YAG laser perforation process of several common plastic films including biaxially-oriented polypropylene (BOPP), biaxially-oriented polyethylene terephthalate (BOPET) and low density polyethylene (LDPE) films. Films were perforated under various pulse energies of 50, 150 and 250 mJ and with pulse duration of ~10 ns and pulse repetition of 1 Hz. It was found that, BOPP, BOPET and LDPE films could be perforated using our developed Nd:YAG laser perforating system. Perforation width or diameters of all films increased with increasing pulse energies. Observed perforations were different among the three film types. For instance, at the pulse energy of 150 mJ, average microperforation diameters of BOPP, BOPET, and LDPE were 51.9, 57.5, and 31.0 microns, respectively. Overall results clearly demonstrated that a Nd:YAG laser perforation process used in this study was effective in developing breathable packaging films with tailored oxygen permeation property. Commercial BOPP films containing 200-1,400 micro-perforations/m2 (average perforation diameter of  50 µm) showed a significant improvement in oxygen transmission rates (OTR) of 25-700% over that of the regular BOPP. Very high OTR films of 16,000 cc/m2.day could be effectively produced for the micro-perforated BOPP, where OTR values of close to 20,000 cc/m2.day was obtainable in the case of BOPET films.

β-Crystal Development of Isotactic Polypropylene during Sheet Extrusion Process

The objective of this study is to correlate the crystal structure with material and processing parameters, in particular -nucleating agent and degree of supercooling. The selected -nucleating agent used in this study was “Quinacridone pigment, E3B” with concentration varied from 1 to 100 ppm. The degree of supercooling during sheet extrusion process was controlled by chill roll temperatures in a range of 60 to 115oC. Crystal structures in neat PP and PP-E3B samples were characterized using WAXD and DSC techniques. The selected PP-E3B, with optimum concentration of 5 ppm, was fabricated into sheets using chill roll temperatures of 60, 70, 80, 90, 100, 110 and 115oC; these sheets had -crystal content (K-value) of about 0.099, 0.214, 0.341, 0.430, 0.651, 0.754 and 0.892, respectively. The melting characteristics and physical properties of the nucleated iPP were also dependent upon -crystal content. Finally, it could be concluded that the development of -crystal structure was highly influenced by the concentration of nucleating agent and processing conditions during sheet extrusion.

Effect of Montmorillonite Content on Nucleation of Polypropylene

In this article, the effect of montmorillonite (MMT) concentration on the nucleation of polypropylene (PP) was investigated. The PP/MMT nanocomposites containing various content of MMT (0.075-3.0 wt%) were prepared by a melt blending process using an internal mixer, followed by compression molding into sheets. The nucleation effect of MMT was characterized by X-ray diffraction (XRD), wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) techniques. XRD results indicated that the PP nanocomposites loaded with less than 1.5 wt% of MMT formed an exfoliated structure. DSC results showed that the crystallization temperature (Tc) of PP/MMT nanocomposites were higher than that of neat PP. Tc also increased with increasing MMT content, indicating that MMT was effective in nucleating PP crystal. WAXD patterns revealed that the addition of MMT did not affect the crystal structure of PP. Mechanical property tests showed that the tensile and impact strengths of the PP/MMT nanocomposites were better than those of neat PP when the MMT content was lower than 1.5 wt%.

Biaxially Drawn Behavior of α- and β-Polypropylene Films under Simultaneous Stretching

This study investigated the biaxially drawn behavior of polypropylene (PP) containing different crystalline structure in between of either α-monoclinic or β-hexagonal crystal form or a combination of both. The precursor sheet with α-crystalline PP was prepared from neat resin using the sheet extrusion process. The high content of β-crystalline phase (K-value of about 84%) was developed in the polypropylene sheet using a proprietary type and concentration of β-crystal nucleator. Biaxial film stretching was carried out using a laboratory stretching machine at the temperature of 145°C. Stretching speed and stretch ratio were kept relatively constant at 400 %/sec and 5.5 x 5.5, respectively. β-PP sample demonstrated a distinct biaxially drawn behavior as compared to that of the neat-PP sample, in particular, biaxial yield stress of neat PP (α-PP) was 3.55 MPa, where a much lower biaxial yield stress value was apparent for β-PP (~1.69 MPa). Interestingly, the total calculated area under stretching curves of the β-nucleated PP sample was about 34.8 % lower than that of the neat PP sample. These findings indicate the less energy required for stretching process of β-nucleated PP. Moreover, the drawn β-PP films also showed comparable mechanical properties to the α-PP sample as well as a good optical property, evidenced by low haze values of <1% which was close to that for the normal BOPP films.

Antifungal activity of plant-derived compounds and their synergism against major postharvest pathogens of longan fruit in vitro

The aim of this study was to find alternatives to conventional synthetic fungicides to control postharvest decay of longan fruit. The antifungal potential of thymol, carvacrol and trans-cinnamaldehyde was evaluated against four major longan pathogens, Lasiodiplodia spp., Phomopsis spp., Pestalotiopsis spp. and Geotrichum candidum, using vapor phase and direct contact methods. The vapor phase of all active compounds was more effective on fungal growth than direct contact. A volatile vapor of thymol and carvacrol had strong antifungal activity against the tested fungi, exhibiting minimum inhibitory concentration (MIC) in the range of 40 to 80 mg/L air; trans-cinnamaldehyde showed the least efficiency, with MIC ranging from 80 to 160 mg/L air for G. candidum and Phomopsis spp., while it could not inhibit Lasiodiplodia spp. and Pestalotiopsis spp. at 160 mg/L air. The minimum fungicidal concentration (MFC) of thymol and carvacrol varied from 40 to 80 mg/L air, while trans-cinnamaldehyde completely inhibited the mycelial growth of the tested fungi at higher concentrations. Mycelial growth of all tested fungi decreased with increasing active compound concentration, except for trans-cinnamaldehyde. Thymol proved to be the most effective compound against the four tested fungi, with effective concentration 50 (EC50) of 5.68 ± 0.59, 6.86 ± 0.52, 8.27 ± 0.22 and 9.99 ± 1.28 mg/L air for Lasiodiplodia spp., Phomopsis spp., Pestalotiopsis spp. and G. candidum, respectively. Fungal growth curves were adequately fitted (0.958 < R2 < 0.996) by a modified Gompertz model. For all tested fungi, the lag phase (λ) of fungal mycelia exposed to thymol and carvacrol increased, while the maximum colony diameter (A) and maximum growth rate (vm) decreased. A combination of thymol and carvacrol exhibited an antagonistic effect against G. candidum but an indifferent effect against Lasiodiplodia spp., Phomopsis spp. and Pestalotiopsis spp.

Low Haze and Antifog Performance of 2-Layer Poly(Lactic Acid) Based Films

For fresh-cut and ready-to-eat packaging films, antifog additives (AFs) are commonly used to suppress the formation of water droplets on film surface. To date, the type and dosage of antifogging for PLA based film are less studied. Therefore, in this research, films incorporated with antifog additive were fabricated by cast extrusion technique. The migration behavior of commercial polyglycerol ester as selected AF was investigated. The cold fog test results showed that 3.5 and 5 wt% of AF in 20PBAT/80PLA single layer film can provide clear films without droplet of water within 7 days and 3 hours, respectively. For 2-layer films, the presented of AF in seal layer as 95(20PBAT/80PLA)/5 (polyglycerol ester) and core layer of PLA were prepared having different thicknesses of seal layer/core layer of 20/15 and 10/15 μm. The migration rate of AF in thin 2-layer film (10/15 μm) appeared to be higher than that in 20/15 μm film. Films’ surface could become clear without water droplet (rating scale > 8) within 4 days for 10/15 μm and 7 days for 20/15 μm films. Haze of films was analyzed by haze meter. Haze of 10/15 μm film was decreased from 7 to 4.4, while that of 20/15 μm film was also decreased from 10 to 7.9 when AF appeared on its surface. Both films can be a peelable PLA based lidding film product with low haze (< 10 %) and antifog performance (within 1 month). In addition, 10/15 μm film can be an easy peel lidding film since its peel strength was in an easy peel range (6-10 N/15 mm).

Biaxially-Stretched Poly(Lactic) Acid (PLA) and Rubber-Toughened PLA Films: Tensile and Physical Properties

Poly(lactic) acid (PLA) is bioplastic produced from corn starch; its brittleness limits the use of PLA in many applications. Biaxial stretching is one approach adopted by film manufacturers to enhance the properties of plastics such as polypropylene (PP). This study aims to produce biaxially-oriented PLA films which had been toughened with 1-10% core-shell rubber (CSR). Differential scanning caloriemetry (DSC) results indicated that all biaxially-stretched neat PLA and the PLA/CSR films possessed nearly 20% greater crystallinity than the as-cast film.The yield stress of the biaxially-stretched films were higher than that of the unstretched films in both machine (MD) and transverse (TD) directions. After biaxial stretching, the elongation at break of the stretched films was still much higher than that of the unstretched ones. The tear resistance was highest in the film with 5 wt% CSR, it became higher after biaxial stretching. The water vapor permeation (WVP) was also minimum in the film with 5 wt% CSR. The biaxially-stretched films had lower WVP than the unstretched ones due to the enhanced crystallization and chain orientation in the stretched films.

Effects of Phthalocyanine Blue and Ultramarine Blue Pigments on Nucleation of Polypropylene

This study investigated the effect of the organic phthalocyanine blue and inorganic ultramarine blue pigments on nucleation of polypropylene (PP). The PP/pigment pellets containing various concentrations of each pigment (0.0001-0.1 wt %) were prepared by a melt blending process using a single-screw extruder, followed by fabricating into thin sheets using a single-screw plastic sheet extruder. The nucleation effects of both pigments were characterized by wide angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC) techniques. The WAXD patterns revealed that the addition of phthalocyanine blue or ultramarine blue did not affect the crystal structure of PP. The DSC results indicated that both pigments were able to nucleate PP, where the organic phthalocyanine blue pigment was a very efficient nucleating agent, increasing the crystallization temperature of PP by 15oC. The results of tensile and optical tests showed that the tensile strength and clarity of PP were improved with phathalocyanine blue addition.