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You are here: Home > Technique > Processes > Scientific report of the LGP2 > Converting Biomaterials Packaging > From converting of new packaging to obtention of new functional properties           Update: July 26, 2011
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(May 2011)
 
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Laboratory of Pulp and Paper Science and Graphic Arts

V - Converting Biomaterials Packaging

V - 4 - From converting of new packaging to obtention of new functional properties

3D packaging needs having process expertise but also understanding impact of environmental conditions in case of paper and paperboard packaging. These two key issues are presented in a PhD work on mechanical performance of paper packaging. New processes are also described in order to prepare packaging with biopolymer and cellulose fibres. These biocomposites are stiffer and environmentally friendly but they can also have specific properties and be used to produce active packaging. Indeed a way to increase vegetable shelf life has been studied during the european project SustainPack. Other important functional properties like food contact or archive conservation have been studied in the group and described in detail.

Introduction

Our society is asking for more and more functional packaging. It is now important to have higher shelf life, better communication and new materials inert for health or resistant to external conditions linked to transport.

Therefore, it is important to have a better understanding of mechanical properties but also to find new raw materials and/or new functionalities. In this paper, some short examples of studies realized in the laboratory will be presented. They concerned the area of packaging processes, material behaviours and novel functional properties.

Packaging converting

Compression mechanical properties

During the PhD of J. Viguié, research concerned mechanical performance of paper packaging with an account for cost and weight reduction expected from the market. The main issue is to understand permanence of mechanical properties of fibrebased structures. Two objectives were targeted: optimise use of renewable ressources by keeping material performances. In order to find optimal solution, it was important to understand relationships between mechanical and end-use properties. Therefore, research works have been focused on compression and buckling phenomena depending on box geometry and monotonic or cyclic conditions of compression. Influence of the deformation speed appears not so important in the studied range. All measurements realized allow building a data base proving the influence of dimension ratio on elongation and compression force at break. This ratio influences also buckling phenomena which have been studied in detail: it is complex and difficult to find a simple model based on conventional assumptions. Some tests of cyclic load & unload allow estimating maximal non-reversible deformations during compression. At microscopic scale, non-reversible deformation comes from failure phenomena which create a loss of cohesion of the fibre network. Some experimental results on box with flute G are compared with paperboard box with the same basis weight. Similar compression resistance has been observed between these two materials. However, buckling effects are different and linked to different phenomena.

So as to study accurately the compression behaviour of the box panels, displacement and strain fields have been assessed during the compression by a 3-D image correlation method. Significant strains have been recorded along the horizontal and the vertical edges during the panel buckling. In these regions, the elastic limit is reached very early whereas it is not the case at the panel center even when the maximal stress is attained [Figure 1].

Résistance mécanique en compression (évolution de la contrainte 
   en N/mm2 en fonction de la déformation)
Figure 1 - Résistance mécanique en compression (évolution de la contrainte
en N/mm2 en fonction de la déformation)

3D processing of biocomposites

Use of plastic material is more and more important in packaging industry. However, these materials have to face important problems like waste management or future petrol shortage. In this context, biobased polymers (called biopolymers) are more and more used alone or in biocomposites, meaning reinforced by renewable resources like natural fibres. These composites have a specific behaviour and we have tried to develop a process to obtain 3D trays. Thermoforming and thermopressing have been compared starting from biocomposite films obtained by hot mixing in a brabender [Figure 2].

SEM analyses of biocomposite with 30% of fibres 
   and a biodegradable polyester as matrix.
Figure 2 - SEM analyses of biocomposite with 30% of fibres
and a biodegradable polyester as matrix.

Biopolymers used were a biodegradable polyester (PEM) and polylactic acic (PLLA). Thermoforming has been difficult to realize due to a lower MFI (Melt Flow Index) linked to the presence of fibres. Thermopressing allows making trays which have been used as demonstrators in Sustainpack project. Compression temperature and drying time have been identified as most important parameters. Compression tests realized have shown higher stiffness of tray by comparing the matrix alone and the biocomposites. This could be an interesting property if we want to stack trays on each other. A scientific paper has been recently proposed and gives all details on a recycling analyses made with a spanish partner to complete these results. The main conclusion is that we managed to obtain new efficient and environmentally friendly 3D biopackaging [Figure 3].

Finished Tray obtained by thermopressing of biocomposites
Figure 3 - Finished Tray obtained by thermopressing of biocomposites

New functional properties

Conservation paper for heritage archives

It turned out to be efficient in preventing chemical and physical degradations of the heritage archives. Choice an appropriate single conditioning is the simplest, the most efficient and the cheapest way to prevent, at a large scale, book collections. Our work in that field concerns research on the development of a new conservation paper for active protection against pollution.

The project of research, led in association with the Research Center on the Preservation of the Graphic Documents (CRCDG) and the Laboratory of the Sciences of the Chemical Engineering (LSGC), suggests developing a paper of preservation allowing to protect proarchives from polluting gases in the storage environment and acid gases arising from the degradation of documents. We elaborated a material able of trapping volatil organic compounds modelled by the acetic acid, the sulphur dioxide and azote dioxide. The adsorbant various fillers were the oxide of magnesium MgO, fibers and grains of activated charcoal, the carbonate of calcium CaCO3 and zeolithes. The physical characteristics of papers made with those fillers were optimized by refining, pressing and calendering. This reference corpus was completed by some commercial papers. Fibers and grains of activated charcoal were found better for acetic acid sorption, but they are more expensive.

The chosen approach for the measurement of the capacities of sorption of acetic acid gives a good illustration of the studied system complexity. The paper is a fibrous, porous and hydrophilic material. The measurements show that the capacities of sorption of the papers are very dependent on environmental conditions. In dry atmosphere, they depend mainly on the nature of incorporated fillers, while in wet atmosphere they are almost similar for all kind of papers. As the acetic acid presents a strong affinity with water, it is likely that the moistening of fibers plays a dominating role in the mechanisms of acetic acid absorption. So, in storage conditions where the humidity is close to 50 % RH, the fillers of the paper would play only a minor role in the absorption capacities of the acetic acid [Figure 4].

A gas mixture of nitrogen and acetic acid (concentration C entrée = 
   5,2.10-4 mol/L) crosses a column filled with tested paper fragments
Figure 4 - A gas mixture of nitrogen and acetic acid (concentration C entrée = 5,2.10-4 mol/L)
crosses a column filled with tested paper fragments. Flow at the outlet is bubbled through water
and acetic acid concentration Cs in this aqueous solution is determined by pH measurement.
(PS without any fillers, PCA Activated carbon, PZ Zeolite 13X, PCaCO3, PMgO)

Emballages actifs et intelligents

Nowadays, our society is looking for more intelligent materials. To avoid confusion, it is important to say that intelligent papers and packaging are totally different. Even if there is no standard for paper, intelligent packaging is following clear definition since an European directive from 2004. Indeed intelligent packaging is already standardized [DeJong, 2005; DeKruijf, 2002] thanks to an european project called Actipack (Fair project CT98-4170) which details new directive (1935/2004/EC).

So, one can state that:

Within a collaboration with the university of Aveiro (SustainPack Project), the impact of surface treatment on fibres used in biocomposites was analyzed. The test consisted in checking tomatoes packaging shelf life. An important improvement has been observed with grafted fibres comparing to virgin fibres biocomposites [Figure 5]. Similar study has been made on papers coated with ascorbic acid and preliminary results look promising.

Impact of fonctional fibres used in biocomposite on shelf life 
   of tomatoes packed in a plastic bag after 12 days at 25°C
Figure 5 - Impact of fonctional fibres used in biocomposite on shelf life
of tomatoes packed in a plastic bag after 12 days at 25°C

Food contact

A study was done on aluminium migration in food, at the time of their storage, or their cooking, in aluminium based materials to evaluate the released aluminium amount, and to compare it with the permissible maximum amount to preserve pubic health in order to appreciate if this use of domesticates aluminium could present a potential toxic risk in public health. We confirmed the release of aluminium put in contact with chelating molecules present in food and tested in simple medium; and we showed that this solubilization could be very important and was a function of the nature of the chelating molecule, its concentration, its chemical form and especially of the temperature. The studied salts forms (salts of K+, Na+ and Li+ of the citric acid, the oxalic acid and the lactic acid) enabled us understanding how the modification of a molecule could change the release of aluminium either by modification of the pH, or by modification of the reactivity. We also evaluated the impact of the food matrix on the quantity of aluminium leaching starting from kitchen utensils used for the storage or cooking. Various foods were selected according to their composition in chelating molecules of aluminium. The release of aluminium is a function of food, localization, temperature, time and the type sampling of container. By confronting our results with the various data of the literature and by integrating them in the context of the daily contributions and the safety limits we tried to model the impact of aluminium, according to the released quantities, in our nutrition. This work enabled us to identify possible practices at the risk, to propose a kinetic model and a pretreatment method for reducing the leachability of aluminium.

Conclusions

Packagings are everywhere in our society. They arouse the interest of numerous researchers to understand the influence of the environment, the problems of the new raw materials, and to work out with new expected features. Some examples of this article demonstrate the remaining challenges. They also bring answers, in particular at the level of the mechanical resistances of packaging and use of biocomposites. The new brought features seem very promising in the field of the improvement of the food shelf life.

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