Authors:J. Majumdar, F. Cser, M. Jollands, and R. Shanks
Differential scanning calorimetry has been used to study the heat flow during melting and crystallisation of a range of polypropylene
post-consumer waste (PP PCW) grades and blends. The heat flow curves and the heat capacity curves indicated that the PP PCW
grades and blends contained contaminants even after manual sorting and a cleaning process. The enthalpies of the PP PCW grades
were lower than that for the virgin grades, as a result of degradation. Small amounts of polymeric contaminants (up to 10%)
did not affect the enthalpies of PP PCW although other contaminants may have had some effect. The enthalpies of the PCW blends
could in general be predicted by a linear additive rule, which is of importance for recycling a variety of PP PCW products.
Authors:İsa Doğan Atik, B. Özen, and F. Tıhmınlıoğlu
The novel film structure of corn-zein coated on polypropylene (PP) synthetic film for packaging industry was developed to
examine the feasibility of resulting coated films as an alternative water barrier performance for food packaging. The effects
of coating formulation (solvent, corn-zein, plasticizer concentration and plasticizer type) on final properties of films were
observed. Corn-zein is the most important protein of corn and has good film forming property. Composites structures of PP
films coated with corn-zein were obtained through a simple solvent casting method. Polyethylene glycol (PEG) and glycerol
(GLY) were used as plasticizer to increase film flexibility. Statistical analysis based on full factorial design was performed
to observe coating formulation effects. The high water vapour barriers were obtained for films coated with coating formulation
consisting of higher amounts of corn-zein plasticized by GLY. The lower glass transition temperatures (Tg) of films were obtained by plasticization of films and Tg decreased by increasing plasticizer content. The statistical analysis defined the key parameters of coating formulation that
had major effects on the final properties of coated PP films as corn-zein, plasticizer concentration and plasticizer type.
In conclusion, corn-zein coatings could have potential as an alternative to conventional synthetic polymers used in composite
multilayer structures for food packaging applications.
The effect of addition of silica on the parameters of isothermal crystallization of polypropylene has been investigated. It
was found that the covering of the silica surface by a layer of low-density polyethylene leads to a deactivation of the filler
regarding the positive effect on the polypropylene crystallization rate parameters. Cross-linking of the surface polyethylene
layer results in a stronger attachment of the modifying polymer to the filler surface and the deactivation effect of the silica
surface modification is more pronounced.
Oxidation thermal parameters on samples of polypropylene (PP) stabilized with hydroxytyrosol were determined. For comparison
purposes, α-tocopherol and a synthetic phenolic commercial antioxidant (Irganox 1076), were also analyzed. Oxidation induction
time (OIt) and oxidation induction temperature (OIT) were determined by differential scanning calorimetry (DSC). The addition
of hydroxytyrosol 0.1 mass% to PP was enough to obtain efficient stabilization during processing. Certain decrease in stabilizing
properties of natural antioxidants was observed for compression moulded materials at high temperatures. However, these samples
were still efficiently stabilized in comparison to the pure material. Hydroxytyrosol showed good performance as polypropylene
antioxidant and it might be considered as promising alternative to the use of phenolic synthetic compounds.
The thermal characterization of polypropylene (PP) composites containing untreated and treated zeolite with different silane
coupling agents was carried out using thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) to investigate
the effects of natural zeolite and surface modifiers on melting, crystallization and degradation behaviour of PP. 3-aminopropyltriethoxysilane
(AMPTES), methyltriethoxysilane (MTES) and 3-mercaptopropyltrimethoxysilane (MPTMS) were used as surface modifiers at four
different concentrations (0.5–2.0 mass%). Thermal analyses indicated that silane treatment and 2–6 mass% zeolite addition
have no significant effect on the melting and degradation temperatures of the composites. The crystallization temperatures
of the composites were increased due to the nucleating effect of the zeolite. The influence of the modifiers on the interactions
between PP and zeolite was determined by the activities of untreated and treated zeolite. The maximum interactions leading
to good adhesion were observed in the AMPTES treated composites. Also, non-isothermal crystallization kinetics of the composites
was analyzed using Avrami and Kissinger models.
The mechanical strain-induced βα-transition of a β-phase isotactic polypropylene (β-iPP) was studied by modulated differential
scanning calorimetry (MDSC). Samples were taken after tensile fracture of a double notched specimen from its process and plastic
zones, respectively, and the related calorimetric response was compared to that of the bulk material. In contrast to conventional
DSC results, it was found that the βα-transformation was not completed in the process zone. Furthermore, the melting of the
α-iPP showed both non-reversing and reversing characteristics, whereas the melting of the β-phase proved to be a reversing
process. Therefore, it was recommended to consider the conversion grade of the βα-transformation by the relative change in
the melt flux of the reversing β-melting peak.
Annealing experiments have been carried out just below the melting temperature of both polyethylene (LLDPE) and polypropylene
(PP) and their blends. The total melting enthalpy measured after the annealing cycle was greater by 10-15% with respect to
the value having been measured before it. During the annealing period the heat capacity decreases to a lower value within
the first 2-3 min. Heat capacities of PP (either in pure form or in the blends) measured during the heating cycle following
the annealing cycle have the same value as during the cooling section. The heat capacities of the LLDPE in the heating cycle
following the annealing were those of the preceding heating cycle. The total heat flows in the cooling section following the
annealing cycle were greater than those in another cooling cycle at the same temperatures indicating that the crystallisation
takes place during the cooling rather than during the annealing periods.
The presence of LLDPE decreases the crystallisation temperature of PP. The presence of SEBS in the blend results in a greater
crystallisation temperature than that of pure PP. The crystallisation temperature of LLDPE increases with increasing levels
The use of polypropylene materials in industry for food packaging is increasing. The presence of additives in the polymer matrix enables the modification or improvement of the properties and performance of the polymer, but these additives are potential risk for human health. In this context, an efficient analytical method for the quantitative determination of three antioxidants (2,6-di-tert-butyl-4-methylphenol (BHT), dibutylhydroxyphenylpropionic acid stearyl ester (Irganox 1076), and tns-(2.4-di-tert-butyl)-phosphite (Irgafos 168)) and five ultraviolet stabilizers (2-(2′-hydroxy-5′-methylphenyl) (UV-P), (2′-hydroxy-3′-tert-5′-methylphenyl)-5-chloroben zotriazole (UV-326), 2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-chlorobenzotriazole (UV-327), 2-(2H-benzotriazol- 2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol(UV-329), and 2-hydroxy-4(octyloxy) benzophenone (UV-531)) in polypropylene food packaging and food simulants by high-performance liquid chromatography (HPLC) has been developed. Parameters affecting the efficiency in the process such as extraction and chromatographic condition were studied in order to determine operating conditions. The analytical method showed good linearity, presenting correlation coefficients (R ≥ 0.9977) for all additives. The limits of detection and quantification were between 0.03 and 0.30 μg mL−1 and between 0.10 and 1.00 μg mL−1 for eight analytes, respectively. Average spiked recoveries in blank polypropylene packaging and food simulants were in the range of 80.4–99.5% and 75.2–106.7%, with relative standard deviations in the range of 0.9–9.1% and 0.2–9.8%. Dissolving the polypropylene food packaging with toluene and precipitating by methanol was demonstrated more effective than ultrasonic extract with acetonitrile or dichloromethane for extracting the additives. The method was successfully applied to commercial polypropylene packaging determination, Irgafos 168 and UV-P were frequently found in six commercial polypropylene films, and the content ranged from 166.47 ± 5.11 to 845.27 ± 29.31 μg g−1 and 2.10 ± 0.29 to 19.23 ± 1.26 μg g−1, respectively.
Authors:Viktória Vargha, Avashnee Chetty, Zsolt Sulyok, Judith Mihály, Zsófia Keresztes, András Tóth, István Sajó, László Korecz, Rajesh Anandjiwala, and Lydia Boguslavsky
Commodity polyolefins, namely, polyethylene and polypropylene (PP) are widely used in industry because of their low cost, ease of processing, good mechanical properties, and excellent chemical resistance. These