Packaging, and plastics used in packaging, are seen virtually everywhere in modern developed society. Most of the goods bought by the public in developed societies are packaged, as are an increasing number in developing countries as well. (One side effect from all this packaging has been a constant barrage of complaints from activists that products are “overpackaged” and this excess packaging contributes to our big waste load.) Many companies have reacted and continue to react to these complaints by reducing or changing their packaging to make the final package less complex and/or using less packaging material.
Packaging has been around for centuries, and probably was developed for a number of reasons. These include preservation and stability of products over time and the protection of products from damage, dirt, moisture, etc. Early packaging was quite crude (e.g., the casks and cases of salted meat carried on old sailing ships, which often went to sea for extended lengths of time).
All packaging provides some sort of barrier; this is a primary reason for packaging products in the first place. Packaging protects products from infiltration (or, in some cases, exfiltration, the latter the passing of a material or materials out of the container) of contaminants, of flavor, color, odor, etc., as well as preserving the contents. Glass and metal containers have been used for packaging goods for many years and certainly qualify as barrier packages. As we discuss later, thick glass and metal qualify as “functional” barriers that stop just about everything from passing through them.
Plastics, that is polymers ordinarily made from chemical and petrochemical raw materials, are everywhere around us, in a multitude of goods ranging from small children’s toys to automobile bodies and house siding. Packaging examples are also legion, most visible in food and beverage products but also well known for consumer items such as the ubiquitous “clamshell” clear rigid thermoformed packaging for hardware and “jewel box” cassette cases (and CDs and DVDs themselves). Packaging is the single largest end user of plastic resins in the United States. For many years, packaging has consumed more than one-quarter of all the resins used in any year in the United States.
In this study we look at a very important segment of the packaging industry, that of plastic barrier packaging and the plastic resins that supply these barriers (i.e., polymers that are used in packaging to provide a barrier to some unwanted intrusion in or out of the package). Barrier resins block the passage of several important substances, including oxygen, moisture, odors, flavors, and others.
Different experts and observers use different terms to describe the use and function of plastics in barrier packaging, and most of these terms are somewhat arbitrary. They can also be confusing. First and foremost, this study is devoted entirely to synthetic barrier plastics; that is, those primarily derived from petrochemical feedstocks. We briefly describe cellophane, the one natural barrier film still in some use, but do not include it in our market estimates and forecasts since it is not synthetic and for years it has been considered an obsolete product with a declining market.
Among synthetic resins, many analysts attempt to differentiate between barrier resins and structural resins used in packaging. By defining some limits of gas permeability that constitute barrier properties, resins are placed in one or the other category. BCC Research does not rigidly classify barrier packaging resins in this way, for not only is “barrier” an arbitrary term, but different resins can perform both barrier and structural functions in some plastic packaging structures. All resins discussed and analyzed in this report are considered to be barrier resins, even if their use may predominantly be structural in many or most of their packaging structures.
We do consider polyolefins (polyethylenes and polypropylene), polystyrene (PS), and other such strong support resins to primarily be structural; we call them secondary barrier resins. This is to differentiate them from the primary barrier resins such as ethylene-vinyl alcohol copolymer (EVOH) and polyvinylidene chloride (PVdC). The latter are included in barrier structures strictly for their gas barrier properties.
As good example of combination structure and barrier is the common polyethylene terephthalate carbonated soft drink (CSD) or water bottle. In this application, the primary structural resin, PET, has sufficient barrier against the primary pass-through material (in this case the exfiltration of carbon dioxide “fizz” from the contained soda) to be a used in a simple monolayer plastic structure for many CSDs. However, it is really a relatively poor barrier resin and all CSDs lose “fizz” over time, with this degradation accelerated by exposure to heat; most of us have experienced opening a rather old plastic soda bottle and finding the contents flat. Many major soft drink bottlers now often put “use by” dates, or other means of identifying the package’s age, on CSD bottles
To package a more demanding product such as beer, which can rapidly degrade from oxygen infiltration, a better barrier structure is needed and the plastic packaging industry has been working for several years on this challenge; this was one the most interesting developments around the turn of the century, discussed in our previous updates and still of interest. Plastic, primarily PET-based, beer bottles have been a desired product for years, but at this time the “ideal” plastic beer bottle that can truly preserve beer for the desired period of time is not yet a widespread commercial reality, especially in the U.S.
In many other cases, a multilayer structure (MLS), either laminated or coextruded, is needed to provide both strength and barrier. Some of these ML structures, even for seemingly simple products like snack foods, are wonders to behold and now often have seven or more different plastic layers, each layer providing a different structural, barrier, or adhesive function.
The growth of plastic barrier packaging, in the sophisticated sense used in this report, has been significant since the discovery and development of the first synthetic specialty barrier resin, polyvinylidene chloride, Dow Chemical’s old Saran brand) in the 1950s and 1960s. (Dow sold the household Saran Wrap to S.C. Johnson but retains the trademark in the U.S. for the basic resin products.) The commercialization of ethylene vinyl alcohol came a bit later, in the 1970s. As we said, these two resins are the backbone of high-barrier plastic packaging.
It was the development of coextrusion technology that enabled the efficient manufacture of ML plastic structures in a wide range of thicknesses, in a single pass through one machine. Coextrusion is just that, a process that extrudes more than one type of resin simultaneously through an extrusion die to form an MLS with discrete and independent layers bonded to each other. The development of coextrusion really caused barrier packaging growth to take off in the late 1970s and early 1980s. Before then, ML structures were made by laminating two plastic layers together with heat or adhesives, a slower and intrinsically less efficient process. Lamination still is an important MLS method, especially for resin combinations that are difficult to coextrude.
Adding to the interest in this subject, the barrier packaging industry changes constantly. An ideal polymeric barrier does not exist, and probably never will, since each application has different requirements. In some cases, for example in the packaging of meat, polyvinyl chloride (PVC), a film that is not a good oxygen barrier, has been commonly used to package beef in supermarket meat displays for years, since it keeps beef color red and inviting for the short time it is on display. However, for long-term transport or storage of meat, a good oxygen barrier is needed to prevent spoilage. Newer packaging was required for “boxed beef,” packages of commercial beef cuts (sirloins, round steak, etc.) that are produced at the processing plant and then shipped in refrigerated boxes for direct sale at the supermarket. A common system in use today uses two film layers, a good barrier for shipment that is removed at the supermarket to expose a PVC film that allows oxygen to infiltrate and keep the beef red.
Current barrier packaging plastics are good, but problems remain that restrict their use or hinder their growth in many applications. These include:
Our goal is to describe the most common and popular barrier polymers and their applications, their technology, competing barrier materials, and future trends. We estimate and forecast markets for barrier polymers of several kinds and in several different important markets such as food and healthcare packaging.
Complete Report @ http://www.reportsnreports.com/reports/143529-plastics-for-barrier-packaging.html
