ADMINISTRACIÓN LOCAL JUNTA VECINAL DE VILVIESTRE DE MUÑÓ

Other polysaccharides, like chitin, chitosan, xylans and mannans (both hemicelluloses) can also be used for the production of biobased plastics. They are extracted from marine and agricultural products and are currently mostly used as edible films or as coatings (Mikkonen & Tenkanen, 2012; Weber et al., 2002). These group of materials will not be discussed in detail further in this PhD-thesis.

2.4

Proteins

Proteins are another raw material that can be used to produce biobased plastics. There are plant- based proteins, like soy proteins, zein and wheat gluten and animal-based proteins, like casein and whey proteins. Despite the many research conducted on these proteins, their use as packaging materials is very limited. Because of this, this group of materials will not be discussed in detail further in this PhD-thesis.

2.5

Drop-in bioplastics

Recently, drop-in solutions represent the largest market share of the global biobased plastics production. These drop-in materials are (partly) biobased, non-biodegradable polymers which are chemically identical to the corresponding conventional polymer. Therefore, they can be easily used in the existing infrastructure and they can be recycled along their conventional counterparts. The most important drop-ins are bio-PET (e.g. PlantBottle™, used by Coca-Cola

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and Heinz) and bio-PE (e.g. Actimel bottles from Danone). The monomer ethylene is produced from ethanol, which is fermented from biomass such as sugarcane and sugar beet (European Bioplastics, 2012, 2014a; Tullo, 2008). The terephtalic acid (PTA) that is polymerized with the biobased ethylene glycol (EG) to produce PET is currently still petroleum based. A more biobased alternative is the use of biobased furandicarboxylic acid (FDCA) instead of PTA to produce polyethylenefuranoate (PEF) (figure 1.7). PEF, produced by Avantium (Netherlands), has a better gas and water barrier than PET, but is not yet commercially available (Gotro, 2013; Molenveld & Van Den Oever, 2014).

Figure 1.7: Chemical structures of PTA and FDCA for the production of respectively PET and PEF

(Gotro, 2013)

As drop-in biobased plastics have a chemically identical structure as their corresponding conventional counterpart, their barrier and thermo-mechanical properties as well as strategies to improve their barrier properties and heat resistance are known (e.g. heat-set PET bottles). Therefore, this group of materials will not be discussed in detail further in this PhD-thesis.

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3. Limitations/Challenges

The use of biobased plastics as food packaging material is subjected to different limitations, restricting at this moment their use. The most important reason for these current limitations of biobased plastics compared to conventional plastics is that the latter are a very mature industry, while the biobased plastics industry is still in its infancy. Therefore, many opportunities for improvement of these limitations exist. The main problems associated with biobased plastics are: cost, availability, processing and performance (Petersen et al., 1999; Philp, 2013).

A first big obstacle hindering the widespread use of biobased plastics is their higher price in comparison to fossil-based plastics. This is logical, as the petroleum based industry has an optimized production technology and the economy of scale advantage, whereas the biobased plastics industry (biotechnology) is in its earliest technological developments and difficulties are encountered when scaling up to industrial capacities (Barker & Safford, 2009; Iles & Martin, 2013; Philp, 2013).

The use of biomass as a raw material also causes concerns regarding availability (possible poor harvest, periods of no crop growth) and consistent quality of the finished products (crop quality can fluctuate). The concerns regarding the use of land for growing crops for the production of plastics instead of food or feed are being refuted by the European Bioplastics Organization and the Organization for Economic Co-operation and Development (OECD), who state that biobased plastics rely on less than 0,01% of the global agricultural area of 5 billion ha, meaning that the area used to grow crops for bioplastics is nowhere near being in competition to food and feed (European Bioplastics, 2014a; OECD, 2013). Furthermore, many alternative raw materials (e.g. food waste, inedible plant parts, methane) are currently being investigated. Besides a higher price level compared to conventional plastics and the concerns on availability as well as on the use of land to produce biobased plastics, there are major limitations on the functionality (processing and performance). Chemical companies are not familiar with the new biobased plastics materials (e.g. PLA, PHB,…), which can create the need for an increase in the R&D department or the implementation of a new production process, since biobased plastics can provide difficulties during processing on the current equipment. Furthermore, a lack of knowledge on barrier properties, moisture sensitivity and heat resistance of new biobased plastics materials are still drawbacks hindering the successful market introduction of biobased plastics (Barker & Safford, 2009; Iles & Martin, 2013). An overview of the limitations of some biobased plastics can be found in table 1.1.

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a _{Price of coated cellulose films}

Raw Material Advantages Limitations References

PLA - Relative low price (1,3-2,7 $/kg) - High availability

- Good mechanical properties - Good printability

- Transparent/high gloss/clarity - Broad processing window - Hydrophobic

- Brittleness

- Thermal instability/low HDT - Low melt strength

- Slow crystallization

- Poor heat sealability (sealable at lower T) - Moderate water vapor barrier

- Moderate O2 barrier

Auras et al., 2004; Bolck, 2006; Cabedo et al., 2006; Jamshidian et al., 2010; Markarian, 2008; Mensitieri et

al., 2011; Rhim et al., 2009 ; Shen et al., 2009

PHA - Moderate mechanical properties - Good printability

- Transparent

- Variation in properties (>100 PHAs) - Good thermal stability (end product) - Heat sealable

- Good water vapor barrier - Good O2 and CO2 barrier

- High price (4,5-6 $/kg) - Low availability - Brittleness - Stiffness

- Poor impact resistance

- Narrow T-range for processing - Odor (during processing)

Arrieta et al., 2014a; Bolck, 2006; Bordes et al., 2009; Cyras et al., 2009; Koller et al., 2010; Liu et al., 2006; Modi, 2010; Reddy et al., 2003; Shen

et al., 2009, Sorrentino et al., 2007; Yu et al., 2006

Starch - Relative low price (2,7-6 $/kg) - High availability

- Good melt strength - Heat sealable - Good printability

- Good O2 and CO2 barrier

- Softer and more flexible than PE and PP

- Hydrophilic

- Poor water vapor barrier - Translucent (not transparent)

- Mechanical properties dependent on %RH - Vulnerability to degradation

- Difficult processability (low processing T)

Bastioli, 2001 ; Bolck, 2006; Cyras et

al., 2009; Gennadios et al., 1997 ;

Joshi, 2008; Liu et al., 2006 ; Markarian, 2008; Müller et al., 2011 ; Shen et al., 2009 ; Siracusa et al., 2008; Sorrentino et al., 2007; Yu et al., 2006 Cellulose - High availability

- Good printability

- Good mechanical properties - Transparent

- Good O2 and CO2 barrier

- High price (9,3- 9,6 $/kg)a - Hydrophilic

- Poor water vapor barrier - Not heat sealable - Not thermoplastic

Bolck, 2006 ; Cyras et al., 2009; Shen

et al., 2009 ; Weber, 2000

15 Chitin/Chitosan - Widely abundant

- Good film forming properties - Good mechanical properties - Good O2 and CO2 barrier

- Hydrophilic

- Poor water vapor barrier - Not heat sealable

Darmadji & Izumimoto, 1994; Jo et

al., 2001; Massouda et al., 2011;

Suyatma et al., 2004 Xylans/mannans -Good film forming properties

-Good oxygen barrier -Good grease barrier

- Hydrophilic - Brittleness

- Moderate mechanical properties

Mikkonen & Tenkanen, 2012

Zein -Good film forming properties -Good tensile properties -Good moisture barrier - Heat sealable

- Brittleness Cho et al., 2010; Ghanbarzadeh et

al., 2006; Sozer & Kokini, 2009

Soy protein isolate -Good biodegradability - Poor mechanical properties - Poor flexibility

- Poor heat sealability - High sensitivity to moisture

Chen & Zhang, 2006 ; Cho et al., 2010; Rhim et al., 2007

(Wheat) gluten - Low cost - Good O2 barrier

- Good film forming properties - Heat Sealable

- High sensitivity to moisture - Brittleness

Tanada-Palmu & Grosso, 2005; Türe et al., 2012; Zhong & Yuan ; 2013

Whey protein isolate

- Good O2 barrier - Good aroma barrier - Heat sealable

- Moderate moisture barrier Galietta et al., 1998; Hernando- Izquierdo & Krochta, 2009; Kokoszka et al., 2010; Maté & Krochta, 1996; McHugh et al., 1994

Casein - Transparent

- Good mechanical properties - Good O2 barrier

- Poor moisture barrier - Poor heat sealability

Chick & Hernandez, 2002; Chick & Ustunol, 2006

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4. Barrier properties

4.1

Importance in the food industry

According to Germain (1997) the food product characteristics and the intended end-use application define the specific barrier requirements of a packaging system. Since permeants may transfer from both the internal and the external environment through the polymer, they can cause a continuous change in product quality and shelf-life. The three most important permeants of a food packaging material are water vapor, oxygen and carbon dioxide. The water vapor barrier is especially important to prevent physical or chemical deterioration. A well-selected water vapor barrier is needed to avoid dehydration (fresh food products) or water permeation (dry products) (Germain, 1997). The oxygen barrier is important for oxygen sensitive food products and both oxygen and carbon dioxide barriers are important for modified atmosphere packaging (MAP). MAP is a frequently applied packaging technique in the food industry in order to delay deterioration of foods by retarding or inhibiting microbiological and chemical degradation processes (Arvanitoyannis, 2012). It is of utmost importance that the applied gas atmosphere, which is often a mixture of CO2 and N2, is maintained in the headspace of the package during storage. Hence, gas-barrier properties of the used packaging materials should be sufficient to maintain the desired gas composition. Both low oxygen barrier films (fruits & vegetables) and high oxygen barrier films are used for MAP.