Improvement and application of the properties of t

Performance improvement and application of stretched polypropylene (OPP) bottles

you may have heard before that stretched polypropylene (OPP) bottles will be grandly introduced, and will replace glass, pet and PVC in a large number of condensers of food refrigeration systems and non food containers. However, the predicted breakthrough did not come as scheduled. Of course, PP is cheaper and more heat-resistant than pet, but at the same time, it has low hardness, poor transparency and barrier properties, and is difficult to process. In particular, the processing speed is relatively low, making OPP economically impossible

now, the market's interest in OPP bottles and cans has increased again, and the discussion on the long-awaited breakthrough is endless. Hard OPP containers made by one-step injection stretch blow molding (isbm) and two-step reheat stretch blow molding (SBM) machines are once again claimed to be a good opportunity to reduce the cost of packaging water, fruit juice, hot filled food, dry powder and personal care products. Easy to produce shrinkage, deformation, etc

surendra agarawal, head of food research and development at Kraft, said, "we are looking forward to a step-by-step change in the manufacturing cost of OPP bottles." Compared with glass, OPP bottles are lighter, harder to break and easier to grasp by hand

bottle grade PET has a density of 1.35 g/cc and now sells for 63 ￠/lb, while the density and price of transparent PP copolymer used in stretch bottles are about 0.910 g/cc and 56 ￠/lb respectively. This makes OPP bottles 40% cheaper than PET bottles under the same volume. Agarawal also pointed out that OPP bottles are lighter than PET bottles, and the "actual transparency" is equal to PET bottles

in 2002, about 57billion PET bottles were used in North America, and the high-output rotary reheat stretch blow molding machine can blow 60000 bottles per hour. Opp bottles are currently limited to the narrow application space of infant nutrition and medicine bottles, mainly in Asia and South America. They are mainly made on a one-step injection, drawing and blowing device, which cannot make a difference in the huge U.S. packaging market. Many people in the industry doubt whether the output of PP preforms and OPP bottles can match that of pet

overcome the defects of OPP

until now, the disadvantages in processing speed and physical properties compared with pet have hindered the development of OPP bottles. However, PP supporters believe that these shortcomings are being overcome through advanced equipment, better bottle blank and bottle tool design, and PP resin and additives tailored for bottles

"our research shows that using high-yield equipment and properly designed PP preforms and OPP bottles, it is possible to compete with PET in yield, transparency, hardness, toughness and sensory properties." Said Robert Portnoy, a market developer at ExxonMobil. He believes that OPP bottles are very competitive when they are produced on high-speed rotary reheat stretch blow molding machines (such as those produced by Sidel, SIG corplast or other companies). However, suppliers of competitive equipment point out that one-step injection, drawing and blowing machines and tandem reheat, stretching and blowing machines are also feasible methods

pp is that compared with pet, it has greater resistance to the absorption and dissipation of heat, while the preform wall used in OPP bottles is generally thicker. Therefore, in addition to the low processing temperature (230 ℃) of PP in the bottle blank injection step, its cycle is also long. Opp bottles are blown out at 130 ℃, which has higher energy consumption and longer molding and cooling cycle than pet. As a result, the processing speed is slower than pet

pp stretch blow molding has a narrow processing temperature range of 5 ℃, while pet is 15 ℃, which increases the probability of downtime and defective products. The stretching of PP is also different, which is something that bottle blank and bottle tool designers will have to be familiar with. In order to make the transparency of OPP close to pet, the stretching direction and stretching rate must be improved. Some parts of the preform, such as the bottom and neck, may be less stretched than the bottle body, making them easy to darken

pp's low hardness also means that OPP bottles have less top load and hoop strength than pet. In addition, the unsatisfactory CO2 can be blocked by tightening the screws after padding, which makes OPP bottles unable to be used in carbonated beverages. In order to obtain the same hardness, OPP bottles need a larger wall thickness than similar PET bottles. Because the lower density of PP makes up for the increased wall thickness, OPP bottles are usually lighter than similar PET bottles

the oxygen and CO2 permeability of OPP bottles is about 30 times that of pet, so they cannot be used as barrier containers unless they are coated or co injected with barrier resin

advances in materials are reducing the performance shortcomings of OPP bottles. For example, millad 3988, a high-performance and low residual transparent agent product produced by Milliken merican chemical company, is widely used in OPP bottles used in vitamine, water, tea, fruit juice, detergent and drugs

"our transparent agent has solved some important problems affecting OPP bottles," said Raj batlaw, market development manager of merican. These problems include obscurity (mainly at the neck and bottom), longer cycle time of bottle blank, poor reliability of stretch blow molding process, etc

Exxon Mobil, Basell and atofina launched transparent PP, which promoted the application prospect of OPP in bottle utensils. Special stretch blow molding grade products provide high transparency and fluidity, as well as outstanding hardness and toughness balance

basell provides a metallocene PP for the stretch blow molding market. Metocene x50182 has been tested on the Sidel device. It reduces the blur of the side wall of the bottle to 1.5%, and increases the brightness to 82%

(to be continued)

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