Application problems of barrier packaging plastics

Barrier packaging plastics have application problems

in recent years, the rapid development of packaging industry is due to its ability to protect and stabilize products for a long time, as well as to avoid damage, pollution and moisture. In order to achieve the best protection effect, high barrier materials are the inevitable choice

in a broad sense, barrier packaging has been used for many years. Barrier packaging is designed to protect the products and contents from the infiltration of pollutants, flavors, pigments and peculiar smell. Sometimes, it is also used to prevent the leakage of contents

in other cases, multi-layer structure (lamination or coextrusion) is required to improve strength and barrier performance. Even for seemingly simple products such as fast food, the packaging can be very complex. These multilayer structures often contain 7 or more different plastic layers, and each layer has different structural barrier or bonding effects

synthetic special barrier resin, polyvinylidene chloride (PVDC), came out in the 1950s. After the development in the 1960s, plastic barrier packaging has experienced great development since then. Soon, ethylene/vinyl alcohol (EVOH) was put into commercial application in the 1970s

barrier packaging industry has been changing since then. Because different applications have different requirements, ideal polymer barrier materials do not exist now and may never appear. For example, in some cases, such as PVC film with poor oxygen barrier characteristics, it is often used as meat packaging display in supermarkets, mainly because PVC film can keep meat red and attract customers during display time. However, if meat needs long-term transportation or storage, it must have good oxygen barrier performance to prevent meat deterioration

at present, barrier packaging plastics can really meet the needs. However, problems still exist, which restricts the application and development of barrier packaging plastics in many applications. These problems mainly include:

(I) high cost, which is generally higher than simple single-layer plastic packaging, such as LDPE and LLDPE

(II) when exposed to water, it is particularly easy to pollute and degrade. EVOH is the most suitable material to solve this problem, but hydroxyl not only gives excellent barrier properties, but also makes the material easy to hydrolyze. Therefore, EVOH can only be used as the inner layer of multilayer structure

(III) handling and reuse problems. Most multi-layer packaging contains a variety of plastics (such as HDPE and PET), so it is not easy to mix and reuse

(IV) challenges from alternative materials. Traditional materials such as glass and new materials such as silica glass veneer can provide excellent barrier properties

according to its oxygen and water permeability and permeability, the barrier resin should have the following permeability characteristics of Jason, the first author of the paper:

1. oxygen: a resin whose oxygen permeability (OTR) is less than 2ml/mil thickness/100 square inches within 24 hours under atmospheric pressure. Most oxygen permeability measurements are carried out at a temperature of 73 ℃ and a relative humidity determined according to specific conditions. The oxygen permeability of many traditional resins is 5, while most new resins are equal to or lower than 1. Check the ambient temperature (10 (3) 5 ℃) and humidity (relative humidity no more than 80%) daily. For example, the oxygen permeability of standard metallized PET film does not exceed 0.3; Materials with oxygen permeability less than 0.1 are classified as high barrier materials, including PVDC and EVOH. Other materials strive to find and solve the difficulties and problems existing in the use of users in time, which are listed as medium barrier materials

2. Water vapor (moisture): resin with moisture permeability (WVTR) lower than 0.1. We define and classify the structure of moisture barrier polymers according to the classification of drug blister packaging industry. In other words, films with moisture permeability higher than 0.1 are classified as ultra-low barrier films, films from 0.06 to 0.1 are classified as low barrier films, films from 0.03 to 0.06 are classified as medium barrier films, and films equal to or lower than 0.03 are classified as high barrier films

a variety of resin films with moisture permeability of 1 have been put on the market for many years. Ptcfe is the latest and best moisture proof film at present, and its moisture permeability is lower than 0.3. It is considered to be the only high moisture proof film resin at present. The moisture permeability is generally measured at 100 ℃ and 90% relative humidity