Packaging industry has experienced rapid growth in tandem with the demand of increasing global population, by safeguard for the enclosed product, extending its shelf life, and introducing unparalleled convenience to consumers. In order to provide stiffness/rigidity and guarantee moisture and gas barrier, the majority of flexible packaging structures incorporate a combination of materials, including Polyethylene (PE), Polypropylene (PP), Polyethylene terephthalate (PET), Polyvinylidene chloride (PVDC), and Polyamide (PA), Ethylene vinyl alcohol (EVOH).
However, different materials present in multilayer structures cannot be handled during recycling process, due to different melting points and thermal stability. These material combinations in flexible packaging are therefore considered as non-recyclable with the current sorting and mechanical recycling infrastructure.
Moreover, all non-recyclable plastic packaging will be banned in the European market from 2030. These challenges have forced the packaging industry to urgently seek mono-material solutions capable of meeting the requirements for both mechanical and barrier properties. In this article, let’s briefly explore the highly relevant mono-material polyethylene solutions in flexible multilayer packaging, including BOPE, MDO-PE, and non-MDO-PE.
Challenges for mono-material PE in flexible packaging
The combination of materials proves highly effective as it allows for the integration of all desired characteristics into a multilayer structure. In contrast, achieving the same level of mechanical properties and barrier function poses a real challenge for mono-material PE. Furthermore, cost and feasibility are additional constraints that put pressure on both resin suppliers and packaging producers:
- Mechanical properties: to meet the requirements of various packaging applications, it must achieve stiffness and strength levels equivalent to those of BOPP/BOPET/PA.
- Barrier property: Polyethylene, in general, is commonly utilized as a moisture barrier, and when heightened resistance against moisture is required, high-density polyethylene (HDPE) becomes a favorable option. However, in terms of providing an oxygen and aroma barrier, PE is not as effective as materials like PA, PET, PVDC, or a metallized layer. Consequently, additional barrier materials, such as EVOH, are often incorporated into the multilayer structure to enhance oxygen barrier properties.
- Cost: An advanced PE resin also requires competitive pricing with consistent quality, in order to be commercially feasible.
- Compatible with current machinery: Processability is one of the main features that must be taken into consideration when developing new products. The ability of the materials to be made into films cannot be jeopardized and they should be able to withstand the packaging machines already employed for multi- and mono-material at facilities worldwide, as replacing and/or modifying them may bring great, unwanted costs.
BOPE solution
Current commercial BOPE grades:(advertised information)
- INNATE™ XUS 59910.08 from Dow (1.7g/10min MI; 0.926 g/cm3 density): The polyethylene film comprises a stable 5×9 orientation made on an industrial scale BOPP line with a broad operation window, giving it outstanding physical properties and a narrow-gauge variation so that your products get improved stiffness, toughness, optical properties and low temperature resistance.
- SCGC™ GREEN POLYMER S197F (0.6 – 0.8 g/10min MI; 0.952 – 0.958 g/cm3 density): enhance the performance of existing BOPE film in market to create sustainable products to the world and a big part of our success is credited to Brückner. New offering of mono-material packaging with low haze and low thermal shrinkage.
- SABIC ® LLDPE BX202 (2.1 g/10min MI; 0.921 g/cm3 density): is a linear low density polyethylene resin typically used for the production of biaxial orientated polyethylene (BOPE) via tenter frame technology. Typical applications are food and non-food packaging. SABIC® BX202 facilitates mono-material PE structures. This grade is also available as certified bio-renewable and circular polymer.
- SINOPEC
- BOPE-1: Melt flow rate 2.5g/10min Density 0.922g/cm3 Film TD tensile strength > 70MPa
- BOPE-2: Melt flow rate 2.0g/10min Density 0.924g/cm3 Film TD tensile strength > 70MPa
MDO-PE Solution
MDO film (machine direction-oriented films) made by MDO technology to improve properties of blown or cast film, whether off-line or in-line with extrusion.
MDO film is formed by stretching the film in machine direction (MD), the path in which the film is extruded. Stretching takes place in several steps. In the first step, the film is heated. By going through a set of rollers, revolving at different speeds, the film is stretched in the desired direction. Lastly, after orientation, the film is cooled and annealed in order to relieve stress and set its properties.
The intrinsic properties of HDPE are already relatively good, and the orientation process further enhances these properties:
- High film stiffness (packaging downgauging is possible).
- High TD (Transverse Direction) tear strength combined with MD (Machine Direction) easy tear.
- High transparency and gloss.
- Improved thermal resistance.
- Excellent printability.
The MDO film orientation process is divided into four phases: heating, stretching, annealing and cooling. Depending on the application, the MDO is based on an 8, 10 or 12 roller concept.
- Heating phase (2 or 4 rollers)
The film is conveyed on heated rollers to obtain the required temperature. - Stretching phase (2 rollers)
The heated film is stretched between two rollers to obtain the required stretching ratio. (reach 8-12 for HDPE) - Annealing phase (2 or 4 rollers)
Annealing rolls reduce the stresses created during the orientation process. - Cooling phase (2 or 4 rollers)
The film cools down and compensates for thermal shrinkage.
Current commercial MDO PE grades: (advertised information)
- SCGC™ HDPE H619F (0.7 g/10min MI; 0.962 g/cm3 density) is a high stiffness high density polyethylene resin for co-extrude blown film and machine direction-oriented film applications. The resin is designed to offer good moisture barrier performance, high temperature resistance and high film stiffness when blend with LDPE and LLDPE.
- Exxon Mobil HDPE 7165L (0.65 g/10min MI; 0.961 g/cm3 density) is a high-density polyethylene resin that can be processed on traditional blown film or cast film lines as well as for making oriented films such as machine direction-oriented polyethylene (MDO-PE). Films made from HD 7165L provide excellent stiffness, thermal, stability and processability for both oriented and non-oriented film applications.
- DOW™ DGDA-6098 NT 7 (0.5 g/10min MI; 0.958 g/cm3 density) high density polyethylene resin is designed for use in a variety of blown film applications where excellent processability, stiffness and clarity are needed
- Borouge FB5600 (0.7 g/10min MI; 0.96 g/cm3 density)
- Exxon Mobil HTA 108 (0.7 g/10min MI; 0.961 g/cm3 density)
- Sabic HDPE F04660 (0.7 g/10min MI; 0.961 g/cm3 density)
Non-MDO PE solution
Given that BOPE has to be processed on existing BOPP lines, necessitating specific operational changes or mechanical modifications, its application in Vietnam is relatively new and requires a considerable amount of time to achieve stability.
A similar situation is observed with MDO-PE, as the majority of current film extrusion lines in Vietnam do not yet incorporate an MDO unit. Instead of employing BOPE and MDO-PE, packaging producers in the region are opting for full PE films using non-MDO solutions. Specifically, they combine high-performance LLDPE, such as C6-C8 LLDPE and mLLDPE, with HDPE, forming a structural layer that exhibits strength and moisture barrier properties. This combination is applied to specific uses, such as pouches for detergent and wet product packaging. For dry food packaging, an additional very thin EVOH layer may be applied.
Examples of high-performance grades:
- Exxon Mobil:
- Dow:
- Innate ST100: C8 LLDPE, độ chảy 0.85 (g/10min), mật độ 0.928 (g/cc)
- Innate ST50: C8 LLDPE, độ chảy (0.85 g/10min), mật độ 0.918 (g/cc)
- Innate TH60: C8 LLDPE, độ chảy (0.85 g/10min), mật độ 0.912 (g/cc)
