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PROPILVEN® Resins Features
PROPILVEN® resins have features that allow them to be easily processed and to obtain a good properties balance in the final piece. Among the most outstanding features in this resin can be mentioned:
· Versatility, excellent processing capacity.
· Low density (0.9 g/cm3).
· Excellent toughness, stiffness and hardness balance.
· High heat distortion temperature.
· Outstanding chemical and cracking resistance due to stress under the action of tensile active agents.
· Excellent fatigue resistance in flexion.
· Low water absorption and vapor permeability.
· Good dielectric properties.
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Grades Selection
When selecting a polypropylene resin, it is necessary to consider a group of variables that are able to define its features which are decisive in order to obtain its maximum performance. Among the basic variables we can find: resin type, melting flow index (molecular weight), molecular weight distribution and additives package, which will be described in further detail.
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Mel Flow Index(MFI)
The Melting flow rate (MFR) is a measurement of the resin flowing capacity under controlled conditions and it can be easily measured with an instrument called plastometer, by using extremely low deformation rates, a 230 °C temperature and a weight of 2.16 Kg , according to the ASTM D 1238 Standard. This variable is inversely related to the viscosity and molecular weight (MW), that is to say, as the melting flow index of the resin increases; the viscosity and the molecular weight decreases.
The molecular weight has a strong influence on the performance of finished products. In general, a resin with high molecular weight (low MFR) produces parts with more tenacity. Also, this type of resin will have higher melting resistance and will be more appropriate for such applications as the production of blown bottles and sheets for thermoforming. A resin with low molecular weight (high MFR) could be easily injected due to its lowest melting viscosity, that is to say, it will present a better mold filling, producing brighter parts and shorter cycles.
PROPILVEN , S.A. is able to produce various kinds of polypropylene resins (homopolymers, impact copolymers and random copolymers), in an average melting flow rate, from 1.4 up to 42 dg/min. As market requirements are more demanding which will imply the development of new products and applications and based on the specifications of our license, Propilven is capable of expanding this range from 0.5 up to 60 dg/min.
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Molecular Weight Distribution (MWD)
Molecular weight distribution (MWD) is a measurement of the number proportion (or in weight proportion) of molecules of different molecular weights which compose a sample of polymeric resin. In other words, the MWD indicates the variation in the size of molecular chains. If the molecules have different chain lengths, the distribution is wide. In the case of similar chain lengths, the distribution is narrow. This last case is typical of the polypropylene obtained by controlled rheology.
Controlled rheology PROPILVEN® resins are produced from a high molecular weight polymer base, whose MWD is modified by means of the action of a chemical agent that breaks the chains and produces a resin with a narrower MWD and with a higher flowing index.
Controlled rheology PROPILVEN's resins were specially designed to offer high performance in the production of textile fibers. The multifilaments elaborated with this resins have a lower swelling at the nozzle, less shrinking and a greater uniformity in fibers title. Controlled rheology PROPILVEN® resins of high melt flow rate can be used in the production of fibers with extremely fine denier (less than to 5 denier per filament).
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Additives Package
Due to its chemical nature, the polypropylene is susceptible to degradation when it is exposed to high temperatures, oxygen, sunlight and other environmental conditions, which can cause important changes in chemical structure, physical properties or resin appearance. In order to avoid the polypropylene thermo-oxidative degradation, it is crucial to use ant oxidizing additives to prevent any change in the chemical structure of the resin. Also, it is required to add Anti-UV stabilizers in order to prevent the photo-oxidation in parts that will be subjected to sunlight for long periods of time. There are other additives that are incorporated to the resin to alter its properties and to be used in specific applications according to the most important demands in the market. Nucleating and clarifying agents are used to increase the stiffness of the polypropylene, to decrease the number of cycles and to increase the clarity or transparency in injection molded parts.
In films, it is common to add antistatic, slipping and anti-blocking agents to avoid powder attraction, as well as the adhesion of one surface to another once the film is coiled and to facilitate their handling in processes that are performed after the extrusion.
PROPILVEN® resins offer an additives package that has been carefully selected, with the purpose of preventing degradation during the process or under end use conditions.
Next, different kinds of resins with their additives are mentioned. These resins were designed by PROPILVEN , S.A. to be used in specific applications:
· Homopolymers and random copolymers with anti-static, slip and anti-blocking agents for manufacturing oriented and non-oriented films.
· Homopolymers with process stabilizers to obtain low water carry over in the raffia extrusion.
· Homopolymers and impact copolymers with special additives for the production of injected containers that are to be in contact with food.
· Homopolymers with nucleating agents for thin-wall containers that require high stiffness and fast cycles.
· Homopolymers and random copolymers with clarifying agents to obtain high clarity bottles.
· Random copolymers with low additives migration for the production of medical bottles (oral intravenous solutions, irrigation and other).
· In block c opolymers with additives to avoid long term ageing (used in automobile industry).
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PROPILVEN® Resins Properties
PROPILVEN® resins combine physical-chemical, mechanical, optical and electrical properties which are better than other thermoplastic materials.
Density
Density is the measurement of weight per volume unit of a material at 23 °C . PROPILVEN® polypropylene has an extremely low density, of 0.91 g/cm3, compared to other thermoplastics, allowing the production of lighter goods and a high-performance per kilogram used.
Thermal resistance
PROPILVEN® polypropylene stands out regarding thermal resistance compared with other thermoplastics, thus having an excellent advantage in sterilizing applications and hot filling. Homopolymers grades have a melting temperature of 165 °C , from 135 to 150 °C for random copolymers and around 150 °C for impact copolymers.
Water Absorption
For all purposes, water absorption of PROPILVEN® resins is insignificant. This is due to their a-polar nature. In addition, PROPILVEN® resins properties are not changed by environmental humidity.
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Chemical Resistance
Polypropylene, as well as other polyolefin, is inert to the most common chemical products, even at moderately high temperatures. It is highly resistant to polar organic chemical substances; however, it is subject to swelling or softening in some non-polar solvents, such as benzene, methylbenzene, carbon tetrachloride, etc. This characteristic turns our resin into an excellent material for manufacturing vessels and pipes and for chemical products storage and transportation.
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Cracking Resistance
PROPILVEN® resins do not crack in the presence of detergents or other tensile-active agents under typical test conditions used for poly-ethylene. A blown resin can easily exceed the 1000 hours of the ESCR test according to the ASTM D1693 method. This capability turns our resins into the most suitable ones for producing vessels containing cleaning products, liquid soaps, agrochemicals & disinfectant products.
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Electrical Properties
The excellent insulating properties of PROPILVEN® resins combined with their excellent thermal resistance turns them into an excellent material for electrical applications.
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Hinge Effect
Parts under periodic stress should be designed according to their resistance to permanent oscillations. For this reason, fatigue tests that predict the material's behavior are carried out in order to design on a more accurate basis.
PROPILVEN® resins have a high fatigue resistance, especially in highly oriented thin sections. This transforms them into suitable materials for the production of parts with incorporate hinges, such as: flip-top, lunch box, briefcases, cases, boxes, portable utility box.
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