HALS stabilization of LDPE films used in agricultural applications

The mechanism of stabilization of low density polyethylene (LDPE) films used in agricultural applications with hindered amine light stabilizer (HALS) has been studied under the influence of natural weather for 750 d. The structural modifications in the exposed films were monitored by Fourier transform infrared spectroscopy (FTIR), while the examination of the surface behavior was performed by scanning electron microscopy (SEM). Finally, the stability of the material was evaluated by measuring the percent elongation at break. The performance of HALS in the films was analyzed through a comparative study carried out on unstabilized LDPE samples exposed to the same weathering conditions for 170 d. The FTIR results have shown that HALS reduces significantly the rate of formation of ketone groups in the exposed films due to deactivation of the excited ketonic carbonyls. This indicates the role of HALS to prevent the occurrence of Norrish I and II reactions. On the other hand, the development of vinyl groups at 909 cm^–1 during the exposure period of 750 d is attributed to the photolysis of the ester group of the HALS localized at 1 734 cm^–1 in the film and the photooxidation of the polymer. The decrease observed in the ester band suggests the loss of the stabilizer. For the unstabilized LDPE film, the results have revealed a fast increase in both ketonic and vinyl groups attributed mainly to Norrish II reactions. This resulted in chain scission responsible for both the rapid drop in elongation at break and the considerable deterioration of the surface of the exposed film. On the contrary, the presence of HALS in the film resulted in a large retention of the elongation at break. Moreover, SEM analysis reveals the role of HALS to prevent the surface damage by reducing the number and size of microcracks.     

Crystallization of poly(1‐butene)/hydrogenated oligocyclopentadiene blends

The crystallization process of poly(1‐butene) and its blends with hydrogenated oligocyclopentadiene was analyzed in dependence on composition. Both isothermal and nonisothermal crystallization processes were studied, and the isothermal crystallization process was investigated starting from both the glass and the melt states. Results revealed that spherulite growth rate, overall crystallization rate, and morphology are strongly dependent on crystallization conditions and blend composition. Nonisothermal crystallization data were analyzed according to the theories of Ozawa and Ziabicki. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1677–1690, 1999     

Food packaging based on polymer nanomaterials

Since its starting in the 19th century, modern food packaging has made great advances as results of global trends and consumer preferences. These advances are oriented to obtain improved food quality and safety. Moreover, with the move toward globalization, food packaging requires also longer shelf life, along with the monitoring of safety and quality based upon international standards. Nanotechnology can address all these requirements and extend and implement the principal packaging functions - containment, protection and preservation, marketing and communications. Applications of polymer nanotechnology in fact can provide new food packaging materials with improved mechanical, barrier and antimicrobial properties, together with nano-sensors for tracing and monitoring the condition of food during transport and storage.The latest innovations in food packaging, using improved, active and smart nanotechnology will be analyzed. It will be also discuss the limits to the development of the new polymer nanomaterials that have the potential to completely transform the food packaging industry.     

Properties of polyethylene-propylene blends

High density polyethylene-isotactic polypropylene blends have been analysed using mechanical tensile tests at temperatures (T) ranging from25 up to 150° C and at crosshead speeds ranging from 0.01 to500 mm min^?1. The data have been tentatively interpreted in terms of cold and hot drawing mechanisms, depending on the values ofT andv. Such interpretation is quite different from that previously suggested in the literature. Using the results of this analysis it has been possible, by a suitable choice of the operating variablesT andv to yield ultradrawn blend fibres. Their mechanical properties, obtained at room temperature and at a cross-head speed of10 mm min^?1 have been analysed and discussed.     

Morphology and properties of isotactic polypropylene modified with hydrocarbon resin MBG273. I. Binary blends

We investigated a system formed of isotactic polypropylene (iPP) and hydrogenated hydrocarbon resin MBG273 (up to 30 wt % resin) to study the influence of the composition on the morphology, structure, and properties of its blends and derived films. All the blends, after the mixing of the components in the melt and cooling at room temperature, were formed by a crystalline phase of iPP and by one homogeneous phase formed by amorphous iPP and the MBG273 resin. The presence of MBG273 did not influence the crystalline structure of iPP, which remained, for every blend, α‐monoclinic, but it reduced the crystallization temperature and nucleation density of iPP. Differential scanning calorimetry and dynamic mechanical thermal analysis showed an increase in the glass‐transition temperature with the resin content, confirming the formation of one amorphous phase. Tensile property analysis indicated an increase in Young's modulus and a decrease in the elongation at break of films as a function of the resin content in the blends. The water vapor permeability and tensile mechanical properties were related to an increase in the glass transition with the addition of MBG273. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3454–3465, 2004     

Helicobacter pylori: a eubacterium lacking the stringent response

Accumulation of 16S rRNA and production of guanosine polyphosphates (pppGpp and ppGpp) were studied during amino acid starvation in three wild-type strains of Helicobacter pylori. All strains exhibit a relaxed phenotype with respect to accumulation of 16S rRNA. This constitutes the first example of a wild-type eubacterium showing a relaxed phenotype. The guanosine polyphosphate levels do not rise as a result of amino acid starvation, as expected for relaxed organisms. However, in both growing and starved cells, basal levels of the two polyphosphates appeared to be present, demonstrating that the enzymatic machinery for guanosine polyphosphate production is present in this organism. These findings are discussed within the framework of the hypothesis that stringent control is a physiological control mechanism more important for the fitness of prokaryotes growing in the general environment than for those that inhabit protected niches.     

Isotactic poly(1-butene)/hydrogenated oligo(cyclopentadiene) blends: Miscibility,morphology, and thermal and mechanical properties

The article discusses the influence of the oligomeric resin, hydrogenated oligo(cyclopentadiene) (HOCP), on the morphology and properties of its blends with isotactic poly(1-butene) (PB-1). PB-1 and HOCP are found to be partially miscible in the melt state. Solidified PB-1/HOCP blends contain three phases: (1) a crystalline phase formed by PB-1 crystals; (2) an amorphous PB-1-rich phase; and (3) an amorphous HOCP-rich phase. The optical micrographs of the solidified blends show a morphology constituted by microspherulites and domains of the HOCP-rich phase homogeneously distributed in the intraspherulitic region. DSC and DMTA results show two glass transition temperatures (T_g), different from the T_g values of the plain components. The lower T_g is attributed to the PB-1-rich phase, and the higher T_g, to the HOCP-rich phase. The tensile properties were investigated at 25 and 80°C. At 25°C, the PB-1-rich phase is rubbery and the HOCP-rich phase is glassy, so the addition of HOCP to PB-1 arouses a noteworthy hardening of the samples and this brings an increase of the Young's modulus, E′ (although the blend crystallinity lessens), and decreases of stresses at yielding point (σ_y) and at rupture (σ_r). The 90/10 and 80/20 blends show high values of elongation at rupture (ε_r). At 80°C, the blends show decreases of E′ and σ_r values with the HOCP content. These decreases are attributed to the rubbery state of the phases and reduction of the blend's crystallinity. At 80°C, all the blends show a high value of ε_r. This phenomenon is attributed to the fine-size domain dispersion of the phases and to sufficient densities of tie molecules and entanglements. Finally, the partial miscibility behavior proposed in this article is compared with the miscibility hypothesis reported elsewhere. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1369–1381, 1998     

Structure and Morphology Development in Films of mLLDPE/LDPE Blends During Blowing

Summary: In this work the analysis of the structure orientation, morphology, relaxation time and optical properties of blown films of mLLDPE, LDPE and their blends were performed by using WAXD, SALS, AFM, DSC and rheological and haze tests. For mLLDPE film, the crystals do not present “a”‐axis orientation along the machine direction; a distinct spherulite like superstructure is seen. The film surface is very rough. The values of bulk and surface haze are higher than LDPE and blends, whereas the relaxation time is lower. For LDPE film the (110) planes are parallel and at same time twisted with respect to the layer of the film with the “a”‐axis well oriented along the machine direction. No spherulite superstructure is observed and the surface of the film is more regular. High values of relaxation time are observed. The surface haze is the predominant contribution to the total haze. For the blend films no clear and distinct spherulite structures are observed. The orientation degree increases with composition never approaching that of LDPE. The surface is very more regular and smooth than that of the pure polymers. The haze values are below the values of pure materials. It was underlined that bulk and surface morphology and orientation degree of the crystalline planes along the machine direction dictate the optical properties of the films. Moreover both orientation and morphology are defined by the PE molecular and melt rheology characteristics, processing conditions and blend composition.

Total, bulk and surface haze of mLLDPE/LDPE blend films as a function of composition.     

Melt Mixing of Ethylene/Butyl Acrylate/Glycidyl Methacrylate Terpolymers with LDPE and PET

The chemical modification by melt‐mixing of an EBAGMA terpolymer with LDPE and PET was investigated with the aim to use these EBAGMA/LDPE and EBAGMA/PET blends (in equal weight quantities) as compatibilizer master batches to improve the compatibility of the LDPE/PET system. It is shown that when the EBAGMA terpolymer is melt blended with LDPE, almost 40% of the initial amount of EBAGMA is linked to the LDPE backbone. In contrast, in the case of EBAGMA/PET, FT‐IR spectra indicate the total reactivity between the two components through the reaction of the epoxy group of EBAGMA with the PET terminal groups. SEM analysis shows that both master batches present two well‐interconnected phases.