Blow molding PP bottles challenge PET bottles

2023-10-17 13:47

Polypropylene (PP) has emerged as a formidable contender in the realm of blow-molded bottles, challenging the dominance of Polyethylene Terephthalate (PET) in various applications. PP offers a compelling case for its adoption due to its cost-effectiveness, lightweight nature, enhanced durability, and improved thermal stability, which allows for hot filling. However, it still grapples with some shortcomings, including gas barrier properties and transparency. This article delves into the reasons behind PP's ascent, its applications, and the steps taken to enhance its performance.


 Blow molding bottle

PET Blow Molding Bottle


Due to the following reasons, polypropylene has become a strong competitor for polyethylene terephthalate (PET) blow molding bottle applications: compared with PET, polypropylene is cheaper, lighter, and has better durability. Thermal filling and lower moisture permeability; a certain clear polypropylene with higher transparency and gloss than PET. On the other hand, the recycling time of polypropylene bottles is longer than that of PET bottles. At the same time, polypropylene has a narrower processing temperature compared with PET; the gas barrier performance of polypropylene is not as good as that of PET, and its flexibility is not as good as that of PET, but Producers of polypropylene resins and manufacturers of additives have taken a big step toward overcoming these shortcomings.


Markets/Applications Although the unit price of polypropylene is lower than that of polyethylene terephthalate, adding fillers, additional processing, or adding barrier layers to improve polypropylene's competitiveness relative to PET may reduce its low price. Advantage. However, compared with PET, PP is a more economical choice as a packaging material in many applications. Due to the dialysis of carbon dioxide by polypropylene, polypropylene cannot yet replace PET as a beverage packaging material; but compared with PET bottles, blow molded polypropylene bottles have made certain progress in packaging water, hot juice, ice tea and sports drinks. Polypropylene bottles are becoming packaging materials for excipients, food ingredients, flavorings and other prepared foods, as well as packaging bottles for detergents and cleaning agents. The ever-expanding food containers are a promising future for the development of polypropylene.


Corresponding performance Compared with polyethylene terephthalate, polypropylene is 10-30% cheaper, and its density is smaller than PET (0.9 g/cc vs. 1.35 g/cc), so the mass ratio of polypropylene bottles Polyethylene terephthalate is lightweight.


 Blow molding bottle


Polypropylene bottles can be hot-filled at 100°C, as is the temperature at which juice and jam products are used. In contrast, ordinary PET bottles cannot be filled above the glass transition temperature of 76°C (however, some recent enhancements have allowed PET to be filled at higher temperatures).


The barrier performance of polypropylene to moisture is about 5 times that of PET, but the penetration rate of PP to oxygen and carbon dioxide is about 30 times that of PET. Therefore, PP bottles need a barrier layer to prevent gases from entering or allowing them to escape easily, and PET bottles do not require this barrier layer. In its pure state, PP is not as transparent as PET, so PP needs to add transparent additives to make its transparency similar to PET;


Compared with PET, PP has low thermal conductivity, so it takes a longer time to heat or cool PP during processing, so the PP bottle production cycle time is 25% longer than PET bottles; nucleating agents can speed up the cooling process Crystallization, shortening cycle time, so shortening cycle time can improve transparency. The processing temperature range of PP is only 3-5°C, while the processing temperature range of PET is 10-15°C. When producing blow molded bottles, the equipment of the PP preform production line is compared with that of the PET preform production line. Not so expensive. Processing PP bottles produced by extrusion blow molding can be used to package tomato sauce and seasonings, cleaning products, mineral water, food and beverages.


 PP bottles

PP Blow Molding Bottle


PP bottles produced by stretch blow molding are mainly used for packaging of water, medicines, dried food and flavorings, household cleaners, isobaric water and sports drinks, children's products, household appliances, liquid soaps and detergents. Transparent agent and nucleating agent PP transparent agent is a type of nucleating agent. The addition of nucleating agents can improve the crystallinity of the polymer during the cooling process, accelerate the cooling of the polymer, accelerate the cycle time of the product, and increase the elastic modulus of the polymer. Clarifiers also act as nucleating agents, allowing the polymer to form into pellets (microscopic crystals that form during cooling) that are smaller than the wavelength of visible light, allowing for the dispersion of smaller amounts compared to standard polymers. light, resulting in increased transparency of the polymer.


Not all nucleating agents can be effective clarifying agents. Clarifying agents are generally organic compounds, such as sorbitol, that are soluble in the thermoplastic melt. Nucleating agents generally consist of talc, carboxylates or phosphates and are often insoluble in the polymer melt. Transparent agents have gone through several generations of development. Sorbitol, introduced in the 1870s, still has a wide range of applications, but also has some limitations, such as lack of transparency in certain circumstances and failure to form flakes at high temperatures. Other sorbitol derivatives are solving such problems but still have some unpleasant taste and odor.


Generally speaking, random copolymer polypropylene has better transparency than isotactic polypropylene at the same amount of transparent agent. But polypropylene homopolymers produced with metallocene catalysts have the same transparency as polypropylene produced with Ziaglar Natte catalysts. Better barrier properties Another way to improve the competitiveness of polypropylene relative to PET blow bottles is to reduce the breathability of polypropylene. By using a double-layer structure of polypropylene in the outer layer and ethylene vinyl alcohol (EVOH) with barrier properties in the inner layer, taking into account cost factors, this bottle can be used in food and beverage packaging bottles like glass and PET containers.


 PP bottles


Another way to improve the barrier properties of polypropylene is to use a special coating, such as epoxy-amine coating, to coat the surface of the bottle and then vulcanize it at high temperature. This material, marketed as Bairocade, is produced by PPG and is said to improve the oxygen barrier properties of plastic bottles, whether they are PET, PP or other polyolefins. Improving the performance of polypropylene Even at room temperature, polypropylene bottles generally exhibit lower impact properties compared to PET in the refrigerator or when frozen. Studies have shown that mixing transparent random copolymer polypropylene containing 15% plastic (polyolefin prepared with ethylene/metallocene catalyst) can significantly improve the impact strength of polypropylene bottles. Researchers have reported that in standard testing, the impact strength of blended clear trackless copolymer polypropylene (height 7.8ft) was greater than the impact strength of unblended polypropylene bottles (4.7ft). Conclusion It seems impossible that polypropylene will replace polyethylene terephthalate as carbonated beverage bottles, but there are many other low-cost, high-quality polypropylene that can replace PET blow molded bottles. Primary applications include food, beverage and other product containers. Many of the initial shortcomings of polypropylene are similar to those of PET - poor transparency, long cycle times, large gas penetration rates and low impact strength. Transparent or nucleating agents have been used, the use of barrier layers and metallocene-based Nucleating agents overcome these shortcomings. Along this line, we will further improve the performance of polypropylene and develop the polypropylene market.


In conclusion, the competition between PP and PET in blow-molded bottles highlights the dynamism and adaptability of the packaging industry. As technologies continue to advance and new solutions emerge, the packaging landscape will continue to evolve, offering more sustainable, cost-effective, and efficient options to meet diverse consumer needs. The rise of PP in this context exemplifies the industry's resilience and capacity for innovation.


 PET bottles