being based on a mixture of proteins β‐lactoglobulin (approximately 57%, Mw of 18 kDa), α‐lactalbumin (approximately 20%, Mw of 14 kDa), bovine serum albumin, and immunoglobulins, among others. Formation of whey protein films involves heat denaturation in aqueous solutions, breaks existing disulfide bonds, and forms new intermolecular disulfide and hydrophobic bonds [151]. Films based on whey protein isolate (WPI) have shown promising mechanical properties as well as moderate water vapor permeability and good oxygen barrier properties [152, 153]. Nevertheless, the properties of WPI films are highly affected by relative humidity (RH) and the type and concentration of plasticizer [154, 155].
1.4 Concluding Remarks
Due to their low cost and high‐performance characteristics, fossil derived polymers have remained as the most preferable materials for packaging applications. However, as mentioned throughout this chapter, serious environmental issues along with the limited natural resources have led to an increase in the development and use of biopolymers as potential strategies to generate novel packaging items. Currently, there are still challenges to overcome, since the material performance of biopolymers in terms of mechanical, thermal, and vapor and gas barrier properties still needs to be further improved to be able to compete with the current petrochemical plastics commonly found in the food packaging industry. Furthermore, ethical issues frequently arise when attempts are made to use biomass for industrial purposes.
According to the European Bioplastics, the global production capacities of bio‐based plastics, biodegradable or not, amounted to 1.7 million tons in 2014. This translates to approximately 680 000 ha of land. Consequently, the surface required to grow sufficient feedstock for current bioplastics production is only about 0.01% of the global agricultural area of a total of 5 billion hectares. In any case, the bioplastics industry is also researching the use of nonfood crops and biomass derived from algae, that is, the “second and third generation feedstock”, respectively, with a view to its further use. Innovative technologies are currently being focused on nonedible by‐products or waste materials as the source for bioplastics. In this regard, the trend for the development of the next generation of bioplastics is currently led by the emergence of conventional polymers made from renewable and nonfood sources. This generation feedstock is based on the production of plastics from cellulosic materials derived from food crop by‐products such as straw, corn stover, or bagasse, which are usually left on the field where they biodegrade at a quantity far higher than necessary to restore the soil carbon pool. At best they are used to produce the energy for the conversion process to feedstock. This leaves significant potential for using biotechnological processes to create a platform to generate chemicals for industrial purposes, the so‐called biorefinery concept, which includes the production of bioplastics. Indeed, the word “sustainable” means to maintain or keep going continuously and the word has been used in connection with forest management for over a century.
Although the renewable source may not be necessarily pursued in packaging applications, it can be still regarded as a remarkable plus, especially in times when oil prices are being increased markedly. However, it is also worthy to note that currently less than 6% of petroleum is addressed to produce polymers in the plastic industry. As a result, the real key property associated with biopolymers from an environmental point of view would be to develop polymers being readily biodegradable. Some plastic parts made of biodegradable polymers can additionally meet the requirements of harmonized standards for compostable materials. Today, a lot of different European and International Standards exist for biodegradable polymer‐based materials (e.g. EN 13432 or ASTM D6400). They are mainly dealing with natural degradation under specific environmental conditions, particularly for packaging waste.
Looking at the end‐of‐life options for biopolymers, different recovery and disposal paths can coexist. In most countries, no separate collection system for biopolymers is established. In USA and Western Europe, highly developed separate collection systems for packaging waste exist and littering of plastic waste present a minor problem. However, waste disposal represents a serious problem for other countries where the recycling rates are still low and waste management is not properly working. Beside residual waste, the mixed plastic fraction from waste sorting can be supplied to waste incineration. During quaternary recycling, the resulting steam can be used in energy production, heating, and solid recovered fuel production. Secondary (mechanical) and, even, tertiary (chemical) recycling of biopolymers, particularly relevant if they are not biodegradable, is also possible. However, these processes would first require appropriate separate collection systems, which are difficult as biopolymers are still present in minor amounts and a wide range of bioplastics and their blends coexist on the market. At this moment, the mechanical recycling of biopolymers is at its beginning and the market penetration is not high enough to make recycling of biopolymers profitable. Furthermore, modern recycling processes, which are state of the art for commercial polymers, will have to be adapted to handle bioplastics properly. For instance, owners of recycling plants should make an effort to ensure that no mixed PLA‐ and PET‐fractions are getting into bottle‐to‐bottle recycling.
Biodegradable packaging is expected to solve the solid waste problem as well as the litter problem. Nevertheless, the current situation indicates that only a few cities are able to collect and compost green waste. Converting a solid material to a gas via biodegradation or composting could not be sustainable if the collecting system is not prepared. In such cases, it is much better to recycle or recover the embodied energy through incineration. Therefore, there is a need to close the resource loop and make the most out of the material rather than simply use it once. Composting, both industrial or home types, is the expected option for biodegradable polymer-based packaging in a near future. This should be considered after material recycling and before thermal utilization. The production of humus‐rich compost from different organic waste is a kind of material use. However, home composting rarely leads to success in terms of complete decomposition in an adequate period of time. Most of the biodegradable polymers are only usable for industrial composting. Nonbiodegradable biopolymers in addition to conventional fossil derived polymers can have a negative impact on the composting process. Additionally, owners of composting plants are not always pleased with the development and introduction of compostable articles either. In recent years, some labeling for compostable packaging materials has been developed, though they do not necessarily give information about the renewable material content.
Overall, although promising steps have been done in the area of biopolymers and new law regulations are pushing toward the use of such materials, more advances need to be carry not only to enhance material performance but also in terms of market possibilities. Current bioplastics should be in a near future more cost‐effective, easier to process, and with enhanced performance so that food packaging users will fully benefit from their use and also, in terms of policy regulations, the use of such materials can be standardized in the food packaging industry.
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