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IR spectrum of an epoxy-anhydride coating
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Part 2 of this review of can coatings discusses issues such as the functional requirements for different types of can coatings, formulation, test procedures and HSE-related matters. Internal coatings for food applications in particular must satisfy a number of requirements in relation to impermeability and lack of both migration and reaction betwee...
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Context 1
... approach allows for comparative analyses to be made between the wet coating and the dry coating of the same formulation. 19 An example of an IR spectrum is given in Figure 6, representing a cured epoxy-anhydride coating. ...
Context 2
... an epoxy-based coating, the epoxy functionality is of considerable importance as it governs the subsequent residual reactivity of the coating. Relevant to this epoxy functionality, in Figure 6, the epoxy -CHOCH-band is visible at 900cm -1 . The -CH2-stretching peaks derived from the epoxy compound are shown at around 2900cm -1 . ...
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Citations
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This work reports an effective laser synthesis of CuO nanoparticles, seeded in cellulose acetate butyrate (CAB). The structure and composition of the resulting nanocomposite were confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Uv–visible spectroscopy, Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC), Raman spectroscopy and Fourier transform infrared spectrometry (FTIR). The characterization data showed that incorporating CuO into the CAB polymer matrix resulted in a heterogeneous organic–inorganic nanocomposite framework, such that suppressed crystallinity, decreased thermostability, and favorably reduced bandgap energy were seen in the CAB/CuO nanocomposite relative to the CAB material itself. The fabricated CAB/CuO nanocomposite was then successfully applied in the reduction of 2-nitrophenol (2-NP), a common organic pollutant in wastewater, where even low concentrations are harmful to human health and aquatic life. The reduction of the 2-nitrophenol compound was carefully monitored by UV–visible absorption spectroscopy. This revealed an apparent rate constant of 0.248 s⁻¹ for the reduction process, demonstrating an excellent catalytic performance by the cellulose acetate butyrate film/CuO nanocomposite. In the technique reported, the reduction efficiency is a factor of time, with 100% efficiency achieved in 16 min.
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In this study, the suitability of four metal powders and one alloy powder for use in composite inks was investigated on the basis of the contribution by each metallic powder to the formulation, printability, hardness, rheology, conductivity and thermal properties of the inks. The effects of the binder chemistry, the composition of the inks and the application conditions on the rheological, electrical, thermal properties of the inks were investigated. The results show controlled film deposition could be achieved by using a screen printing technique. The relationship between the viscosities of the inks with an increase in temperature depends on the metal powder used in formulation and on the polymeric binder chosen. Those inks that were based on the poly(vinylpyrrolidine)-co-styrene (PVS-co-S) have shown an increase in viscosity as the flow temperature was increased above 60 oC. The resistance properties of these inks depend on the temperature at which the inks were dried. This can allow for a control on the flow of electrons in the ink prints and a balance between print hardness and electrical properties to be achieved. Of the three substrates that were used in the studies, the inks applied onto the tinplated steel and onto the PET substrate showed signs of ink delamination, after drying. However, no such delamination was encountered from the inks that were applied onto the paperboard substrate.
The coatings of metal cans may release complex mixtures of migrants into the contained foods, including non-intentionally added substances (NIAS), such as reaction products. All migrating substances should be studied to demonstrate their safety. In this work, the characterisation of two epoxy and organosol coatings was performed using several techniques. Firstly, the type of coating was identified using FTIR-ATR. Screening techniques based on purge and trap (P&T) and solid-phase microextraction (SPME) coupled to GC-MS were used to investigate volatiles from coatings. For the identification of semi-volatile compounds, an appropriate extraction was performed before analysis by GC-MS. The most abundant substances were compounds with at least one benzene ring and an aldehyde or alcohol group in their structures. Furthermore, a method to quantify some of the identified volatiles was explored. Secondly, HPLC with fluorescence detection (HPLC-FLD) was used to determine non-volatile compounds such as bisphenol analogues and bisphenol A diglycidyl ethers (BADGEs), with subsequent confirmation by LC-MS/MS. Additionally, migration assays were performed by this technique to determine non-volatile compounds migrating into food simulants. Bisphenol A (BPA) and all BADGE derivatives except BADGE.HCl were detected in the migration extracts. Moreover, BADGE-solvent complexes such as BADGE.H2O.BuEtOH, BADGE.2BuEtOH, etc. were also tentatively identified using the accurate mass provided by time-of-flight mass spectrometry (TOF-MS).
Canned food and beverages have long been recognized as an integral part of food preservation and long-term storage in the global food supply chain. Advantages of metal cans include low cost, durability, long shelf life, tamper resistance, ease of storage, well-established infrastructure, and recycling processes. The internal surfaces of most food and beverage containers are typically coated with organic coatings that provide one or more properties, including serving as barriers between the metal can and its contents. There are several regulations in 21 Code of Federal Regulations (21 CFR), as well as effective food contact notifications (FCNs), that pertain specifically to organic coatings. This chapter will discuss the technology behind can fabrication and processing of can contents, the US regulations pertaining to can coatings, and highlight some of the recent research on can coatings.
Major type of internal can coating used for food and beverages is made from epoxy resins, which contain among their components bisphenol A (BPA) or bisphenol A diglycidyl ether (BADGE). These components can be released and contaminate the food or beverage. There is no specific European legislation for coatings, but there is legislation on specific substances setting migration limits. Many investigations have paid attention to BPA due to its classification as endocrine disruptor, however, few studies are available concerning to other bisphenol analogues that have been used in the manufacture of these resins.
To evaluate the presence of this family of compounds, ten cans of beverages were taken as study samples. Firstly, the type of coating was verified using an attenuated total reflectance-FTIR spectrometer to check the type of coating presents in most of the samples examined. A screening method was also performed to investigate potential volatiles from polymeric can coatings of beverages using Purge and Trap (P&T) technique coupled to gas chromatography with mass spectrometry detection (GC-MS).
Moreover, a selective analytical method based on high performance liquid chromatography with fluorescence detection (HPLC-FLD) for the simultaneous identification and quantification of thirteen compounds including bisphenol analogues (BPA, BPB, BPC, BPE, BPF, BPG) and BADGEs (BADGE, BADGE.H2O, BADGE.2H2O, BADGE.HCl, BADGE.2HCl, BADGE.H2O.HCl, cyclo-di-BADGE) in the polymeric can coatings and in the beverage samples was applied. In addition, a liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) method was optimized for confirmation purposes.
The method showed an adequate linearity (R² >0.9994) and low detection levels down to 5 µg/L. Cyclo-di-BADGE was detected in all extracts of polymeric coatings. The concentrations ranged from 0.004 to 0.60 mg/dm². No detectable amounts of bisphenol related compounds were found in any of the beverage samples at levels that may pose a risk to human health, suggesting a low intake of bisphenols from beverages.
In this study, the suitability of four chemically different melamino cross-linkers for use in formulating epoxy coatings was investigated on the basis of the composition and of the tendency of cured coatings to hydrolyse to melamine and to formaldehyde when they were retorted in aqueous food simulants. The four cross-linkers were characterised for their composition identity, flow behaviour, thermal stability and for the presence of residual species. The different cross-linkers were used individually to cross-link selected epoxy coatings. The effects of the cross-linker chemistry, the curing conditions and the kinetics of the hydrolysis and subsequent migration processes, leading to melamine and formaldehyde were investigated following thermal treatments that were designed to represent the conditions of food sterilisation. The results show that each cross-linker type is different in its rheological characteristics, its solids content, its thermal behaviour and its physical properties. The chemistry of each cross-linker plays a major role in the manner in which the epoxy coatings undergo hydrolysis to release melamine and formaldehyde. The greatest migration of melamine (from an unpigmented epoxy anhydride coating, cured with the hexamethoxymethyl melamine cross-linker) into the 10% (v/v) aqueous ethanol food stimulant, after retorting at 131 °C, for 1 h was 525 μg/6 dm2. The greatest migration of formaldehyde into the simulant was also from this coating at 11 μg/6 dm2, when retorted at 131 °C for 1 h. The curing conditions affected the extent of the cross-linker hydrolysis. The influence of varying the curing time and the curing temperature was used to control the hydrolysis of the cross-linked, epoxy-based coatings. A decrease in the extent of cross-linker hydrolysis by 50–80% was achieved in all cases as the temperature of the curing was increased, in stages, from 160 °C to 200 °C.
