Biodegradable packaging plastics

Fig. 7. Twin-track testing protocol for biodegradable packaging plastics...

Polyesters and polyamides are the most prevalent of this type of polymer. Poly(ethylene terephthalate) is used in bottle manufacture and along with other packaging plastics is not biodegradable. Potts(54) established very early that only low melting and low molecular weight aliphatic polyesters were biodegradable. 

Polymer blends, particularly olefins with biodegradable polymers, are gaining popularity as an approach to degradable packaging plastics. The materials are at best only partially biodegraded, but will lose form and bulk as the plastic disintegrates. This may be sufficient in landfill as volume diminishes, leaving room... 

A second approach to biodegradable packaging is to blend polyethylene with a second synthetic polymer with polar repeating units that are capable of degradation, such as ester linkages (chapter 12). Poly(caprolactone) represents such a class of polymer, which has a long history of compatibility ( with a variety of polymers and degradability (5) recently, improved miscibility and Glm properties have been reported when poly(caprolactone) is blended with commodity plastics... 

The world biodegradable plastics industry has agreed a set of standards and certification procedures for biodegradable packaging materials, which will continue to encourage growth and possibly deter imitation. 

PLA is known both as poly(lactic acid) and as polylactide. It is currently the most used packaging plastic that is both biodegradable and biobased. PLA is a member of the polyester family, and is chemically synthesized from lactic acid that is derived from starch by fermentation. PLA has the following structure ... 

An important use of PS is in foams and beads which are widely used as impact absorbing materials in packaging. Because of its very low bulk density, expanded PS is a very visible component of plastics litter and is often seen floating on the surface of water. For the same reasons it is particularly expensive to collect and reprocess. Biodegradable foamed plastics based on starch are being developed which promise to be an ecologically acceptable alternative to PS (Chapter 5). 

An improvement in terms of flexibility for PLA may widen its application as a biodegradable packaging and film material. The addition of plasticizers has been investigated lately in order to improve the fragility and increase the elongation of break or elasticity of PLA. Previous researchers have shown that addition of plasticizers such as polyethylene glycol (PEG), glucosemonoesters and partial fatty acid esters had successfully overcome the brittleness and widen PLA s application [2, 7, 8]. 

It is now January 1993, and the public is perceiving that the United States is burying itself in solid waste materials. ConAgra, Inc., has approached DuPont with a proposal for a joint venture to produce lactic acid for conversion to biodegradable polylactide plastics to be used in packaging and other markets that might help to alleviate the solid waste problem. 

It is estimated that approximately two-fifths of the total plastics is used in packaging and about 50% of that is used in food industry as a packaging material. Since large volume of the inert materials is disposed of as waste-land fillers, therefore, people all over the world are trying to use the biodegradable packaging materials so as to reduce the volume of waste materials. 

McCarthy-Bates, L., Biodegradables Blossom into Field of Dreams for Packagers, Plastics World, March 1993, pp. 22-27. 

The tendency for PLA plasticized with PEG to lose properties with time at ambient temperature is a major obstacle to its application as a biodegradable packaging material. Without plasticizer, PLA is stiff and brittle. Blending with low molecular weight PEG improves elongation at break and softness. The desired mechanical properties are achieved in quenched PLA/PEG blends with 30 wt% PEG However, the blends are not stable at ambient temperature and the attractive mechanical properties are lost over time. Crystallization and phase separation are possible aging processes. 

Evaluation of the disintegration of packaging materials in practical oriented tests under defined composting conditions Plastics—evaluation of compostability -test scheme and specifications Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium—method by measuring the oxygen demand in a closed respirometer (ISO 14851 1999)... 

This international standard is very similar to EN 13432-2000 and establishes the performance requirements for biodegradation of plastic materials and products (including packaging, hlms, and other products). The compostable plastics are designed to biodegrade in an industrial compost environment. The industrial compost environment is one that maintains a temperature above 40° C and results in thermophilic conditions. The performance specihcation standard requires the use of EN 14995 (ISO 17088) test method to measure the amount of CO2 that is emitted from the degrading plastic sample. EN 13432-2000 performance specification standard requires the product must demonstrate each of the four following characteristics ... 

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