Succipack
  PROPERTIES OF PBS

Continued from Succinic acid and PBS production

You can also download the final report (PDF document, 30 pages in total).

Barrier properties

Different materials have been studied, in order to establish the possibility to modulate permeation properties through the formulation and through the polymer modification by copolymerization.

An improvement of barrier properties was observed by the use of SiOx coating and the use of green water based coatings but there was no improvement by the use of CxHy plasma treatment by the 3D coating of PBS injected cups. For mineral coatings, best results were obtained with PBSA copolymer surfaces.

The improvement of permeability was finally studied by the modulation of packaging type and thickness. Permeation charts were built to select, from targeted water or oxygen permeability, the best PBS based packaging.
In a nutshell, a very large range of permeability can be accessed thanks to the types of formulation and sample thickness.

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Breathing properties

The permeability analysis permitted to measure the CO2 transfer and its selectivity compared to oxygen. Selectivity is generally higher than the common reported values in literature for classical packaging materials.

Tests with packed fresh-cut lettuce have been practiced in order to compare the commercial packaging film and 3 kinds of PBS based films: PBS (20 µm), PBS (30 µm) and a PBSA/PBS film. The results show that both films allow to obtain the same level of Listeria spp, but with PBS based films a lower level of microorganisms is obtained.

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Mechanical properties

As already underlined, there is a limited choice in commercially available PBS grades. This means that pure materials cover a small range in mechanical properties, while PBS may be used for various packaging applications with different flexibility (from flexible for film applications to rigid for trays applications).
PBS mechanical properties can be adapted to various books of specifications for packaging applications.

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Thermal properties

The review of the thermal characteristics of all PBS polymers produced in SUCCIPACK highlighted that the melting points (Tm) ranged from 109 to 115 °C, with the lowest values documented in the case of bio-based PBS grades (bPBS).

For all PBS grades studied in the project, SSP served as a post-crystallization method. As a result, sharpening of the melting endotherm and increase of the melting point were documented during PBS SSP/SST, reaching an upper limit of ca. 124°C and accompanied in most cases by crystallinity increase.
In a nutshell, SSP represents a useful tool with great potential in the industry towards improving PBS thermal properties.

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Food contact properties

The requirements of European regulations in the field of food safety according to 1935/2004/EC are the following:

  • Basic components of the material are to be included in the positive list;
  • Substances with restrictions must be controlled (specific migration in intended conditions of use must be lower than specific migration limits) either by experimental tests, or with migration modelling;
  • The overall migration must be less than 10mg /dm2 packaging;
  • The contact between the packaging and the food must not cause changes in product organoleptic characteristics;
  • Non intended added substances must be identified and further evaluation is needed for eventual critical substances.

The safety assessment of PBS-based materials is developed in the final report for each requirement.

CTCPA wrote guidelines about the safety assessment of PBS-based. These guidelines have been set up in order to disseminate them to industries and public authorities implied in food packaging safety.

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Susceptibility to hydrolysis

As PBS is an aliphatic polyester, its sensitivity to hydrolyze during both processing (degradation) or storage (ageing) was studied.
Concerning ageing during storage, a simple kinetic model was tested in the project, by measuring the degradation kinetics in different conditions of water content, initial acidic index, and degradation temperature. To reduce the degradation rate of PBS materials, it was also necessary to minimize the initial acidic index, the water content all along the supply chain, and time /temperature effects. The model was validated for PBS homopolymer. Guidelines for PBS material flexible processing have been written by ACTIA to provide processing conditions of PBS packaging materials.

Recommendations

Consequently it is suggested to evaluate the migration of both the unaged (as suggested by the EU regulation) and the aged material:

  • Classical evaluation of the packaging material after processing;
  • Second migration test after artificial aging of the packaging. This artificial aging should cover the worst case period of storage condition of the packaging before food contact and half time of the shelf life food contact conditions.

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Aroma scalping properties

Showing a medium Hildebrand solubility parameter, PBS can theoretically interact with a lot of organic compounds. As a consequence, PBS is predicted to show a potential of high aroma scalping. Moreover due to a low glass transition, the transfer dynamics are supposed to be fast, with a potential effect of quick losses of food organoleptic properties.

For the aroma scalping, the results obtained by the microgravimetric measurements show that the PBS-based films have comparable barrier properties as LDPE films for polar aroma compounds and significantly better barrier properties for compounds of low polarity.

For transfer dynamics, overall evaluation of measured results shows different characteristics especially for the group of PBS based materials and PE based foil as a reference material.

However, despite the observed differences, the behaviour of PBS and LDPE films with respect to the model aroma compounds was generally very close. PBS can then be classed at the level of LDPE for its aroma sorption and transfer properties.

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This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement No.289196
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