Polymers: Polypropylene + Polyamide 6 Blends - Literature review Example

Literature Review Name Institution Literature Review Background Polymers Polymers refer to large molecules or macromolecules which comprise of many recurrent subunits. Polymers have wide range of properties (Morawetz, 2002). Both artificial and natural polymers play significant and pervasive role in everyday life. Polymers are inclusive of wide variety of categories from the common artificial plastics which include polystyrene to the natural biopolymers which include the DNA and other proteins which are very significant to biological composition and roles (Gunatillake & Adhikari, 2003). Both the artificial and the natural polymers are created by the polymerization of numerous micro molecules referred to as monomers. Consequently, they produce large molecules with distinct physical characteristics which include stiffness, viscoelasticity, and likelihood of glass formation and semi crystalline configurations. The term polymer originates from a Greek word ‘πολύς’ meaning ‘many much’ (Huang, Zhang, Kotaki & Ramakrishna, 2003). The word refers to a molecule that is formed from numerous recurrent units from where the high relative molecular mass instigates with distinct characteristics. The original molecules are of low relative molecular weight. There are two types of polymers; natural polymers and synthetic polymers (Morawetz, 2002). Natural polymers include; silk, shellac, wool, and rubber. The synthetic polymers include; PVB, polypropylene, silicone, polyethylene, and polyacrylonitrile. In most cases, the continually connected backbone of a polymer utilized in the development of plastics comprises of mainly carbon molecules. For instance, polyethylene recurrent unit is based on ethylene monomer. Nevertheless, other forms are in existence; silicon form similar products such as silicones. Example of such products include; Silly Putty and water repellant sanitation sealant. Oxygen rarely lacks in the backbones of the polymers which include polyethylene glycol and the DNA (Gunatillake & Adhikari, 2003). Polymerization refers to the process of combining the numerous macro molecules covalently to form a polymer. During this process, various chemical groups get lost form the monomers involved. The particular section of each monomer that is repeatedly unified into the polymer is referred to as the repeating unit. Artificial polymerization methods are of two categories; chain growth polymerization and the step-growth polymerization (Morawetz, 2002). The major dissimilarity between the two methods is that; in the chain growth polymerization, polymers are joined to the chain one at a time. On the other hand, step-growth polymerization, the monomers may join to each other openly. The artificial polymerization methods may utilize catalysts or not (Morawetz, 2002).The natural occurring polymers are of three categories which include; polysaccharides, polynucleotides, and polysaccharides. Naturally, the process of synthesis may be mediated by enzymes. For instance, the process of DNA synthesis involves various enzyme mediated steps. Majority of the commercial polymers are obtained through chemical alteration of the naturally occurring polymers. An example of chemical modification is the process of reacting nitric acid with cellulose in the development of nitrocellulose. Polymers may be modified in various ways such as cross-linking and oxidation (Morawetz, 2002). Polymer properties are of two categories and the most common property is the individuality of the polymer monomer. The other property is referred to as the microstructure which is the prearrangement of the monomers within the polymer at the gauge of a sole chain. The major properties play a significant role in the determination of bulk physical characteristics of the polymer which designates the behavior of unremitting macroscopic material (Huang, Zhang, Kotaki & Ramakrishna, 2003). At the nano-scale, chemical characteristics explain the interaction of the chains through distinct physical conditions. The macro-scale explains the interaction of the bulk polymer with other chemicals and solvents. Polypropylene Polypropylene refers to a thermoplastic polymer utilized in various applications which include packaging, stationery, labelling, textiles, and renewable vessels. Also, it is utilized in the automotive equipment ad loudspeakers. Additionally, there is a polymer developed from monomer propylene (Fallahi, Barmar & Kish, 2011). The polymer is craggy and extraordinarily resists to numerous solvents, basic, and acidic solutions. Majority of the marketable Polypropylene is isotactic and has a moderate density. It is generally hard and elastic especially after copolymerization with ethylene. This makes Polypropylene appropriate for use in engineering plastics together with materials such as ABS. Polypropylene is practically economical and can be produced in the translucent form (Kojima et al., 1993). However, it does not appear transparent ay acrylic and other plastics. In most cases, it is opaque or colored by use of pigmentation. Polypropylene properly resists fatigue and it melts at a range of temperatures. Therefore, the melting is obtained by determination of the highest temperature from a differential scanning calorimeter. Isotactic polypropylene melts at a temperature of 171oC whereas commercial isotactic polypropylene melts at a range of temperature ranging from 160o C to 166o C reliant on the atacticity and crystallinity (Kojima et al., 1993). The melt flow rate refers to a degree of molecular massof polypropylene. This degree assists in the determination of the movement of the molten substance as a raw material in the course of processing. The effect strength reduces with an increase in the melt flow. Polypropylene is of three categories which include; block copolymer, homopolymer, and random copolymer (Zwijnenburg, 2012). The comonomer is generally used in conjunction with ethylene. Ethylene- polypropylene rubber joined to polypropylene homopolymer raises its low temperature impact power. According to Zwijnenburg (2012), Polypropylene is liable to chain degradation from high temperature treatment and Ultra-Violetradiation. Oxidation normally takes place at the tertiary carbon molecule in each recurrent unit. The process leads to the formation of a free radical which reacts with another oxygen molecule trailed by chain scission to form aldehydes and carboxylic acids. In exterior applications, it is seen as chains of fine fissure that deepen and get severe as the exposure time elapses (Morawetz, 2002). For the exterior applications, U.V engrossing additives are utilized. Carbon black is the most utilized in the shield of attack form UV. Additionally, the polymer may be oxidized at extreme temperatures, a recurrent issue during molding processes. Anti-oxidants are very significant in the prevention of polymer degradation (Fallahi, Barmar & Kish, 2011). There are classes of microorganisms that have shown capability to degrade polypropylene. The traditional development of polypropylene involves three distinct ways. The first method utilizes inactive hydrocarbon diluent in the reaction for the facilitation of polypropylene transfer to the catalyst. Also, it facilitate in the reduction of heat in the system and elimination of the catalyst, and in the dissolving of the atactic polymer. However, this process does not produce variety of grades (Zwijnenburg, 2012). The second method utilizes the liquid propylene in place of inactive hydrocarbon diluent. The polymer is not dissolved in the liquid polypropylene, but it floats on the diluent. The resultant polymer is extracted and the un-reacted monomer is discarded. The third method makes use of gaseous propylene in connection with a concrete catalyst, leading to a fluidized-bed medium. Melt process of polypropylene is achievable through either extrusion or molding (Salamone1996). Polypropylene is a chief polymer utilized in nonwovens. Most of it utilized in the manufacture of diapers and other sanitary goods where it undergoes treatment so as to engross water rather than repel it. It is utilized in warm-weather clothing which moves sweat away from the skin. Majority of repair objects are made of polypropylene because it is strong and impervious to majority of glues and solvents (Morawetz, 2002). Polyamide 6 Polyamide 6 (nylon 6) refer to a polyamide from the nylon category (Ozen, Kiziltas, Kiziltas & Gardner, 2013). Nylons are of distinct types and most commonly utilized in the textile and the plastic industries include the nylon 6, and nylon 6-6. Also, nylon 6 is produced by ring opening polymerization of caprolactam. Caprolactam comprises of six carbon atom. When it undergoes heating at 533K in an inactive atmosphere of Nitrogen for about 4.5 hours, the ring discontinues and polymerization occurs. The molten nylon 6 is taken through the spinning process which leads to extrusion of nylon 6 and moved to a spinneret which is a minute metal plate with small holes (Kojima et al., 1993). The polyamide then undergoes cooling resulting to formation of filaments. Reaction process of polyamide 6 formation (Ozen, Kiziltas, Kiziltas & Gardner, 2013) There are various types of polyamides which are either dependent on the type of the monomer or the crystallinity. According to the number of the monomers, polyamides may either be homopolymers or copolymers (Fallahi, Barmar & Kish, 2011). With respect to the crystallinity, polyamides may either be semi-crystalline or amorphous. The difference between nylon 6,6 and nylon 6 is that; in nylon 6,6 the direction of the amide bond is reversed at every bond, whereas in nylon 6, all the made lie in the similar route. Nylon 6 fibers are hard with high possession of tensile strength, resistance, and luster (Ozen, Kiziltas, Kiziltas & Gardner, 2013). The nylon 6 does not wrinkle and it shows high resistant to abrasion and chemicals of both acidic and basic nature. Also, the fibers of nylon 6 engross up to 2.4% of fluids; however, it lowers the tensile capacity. The glass conversion temperature of Nylon 6 is 47o C. Nylon 6 is applied in a wide range of products which necessitate materials of unique strength. In the automotive industries, it is extensively utilized for gears, furnishings, and bearings (Ozen, Kiziltas, Kiziltas & Gardner, 2013). Also, it is utilized as material for power tools covers. Nylon 6 is utilized as yarns in toothbrush bristles, surgical seams, and threads for auditory and classical melodic instruments such as guitars, violins, and cellos. Additionally, it is utilized in the manufacture of wide variety of clothing, ropes, nets and gun frames. Nylon 6 oligomers are degraded by flavobacterium sp. and Pseudomonas sp. However, the bacteria do not degrade the polymers of nylon 6 (Fallahi, Barmar & Kish, 2011). However, particular white rot fungal strains are capable of causing Nylon 6 degradation via oxidation. Nylon 6 has a melting temperature of 220o C and molecular weight of monomer is 113.16 g/mol. The amorphous density of Nylon 6 is 25o C: 1.084 g/cm3 (Kojima et al., 1993). Polypropylene + Polyamide 6 Blend The process of blending polymers is widely utilized in the development of new components. However, this process has one major disadvantage; the polymer components are usually in a non-compatible state and the development of blends with appropriate properties is not satisfactory. An additional compound is utilized during the blending process referred to as a compatibilizer (Salamone1996). The compound effectively ameliorates the final properties of the blend. Compatibilizers utilized for propylene and nylon 6 blend based on grafted or block polyole-fines. Compatibilization extensively affects the blend phase morphology and it also affects the crystallization characteristics of the blend. Both structure and crystallization characteristics are closely linked to the consequential properties of the blend (Krištofič & Ujhelyiová, 2012).Hence, a deep comprehension of the crystallization characteristics is necessary for effectual alteration and regulation of their properties from both systematic and industrial point of outlook. Nevertheless, the overall effect of a compatibilizer on the crystallization characteristic has not been well studied (Fallahi, Barmar & Kish, 2011). In crystalline blends consisting of the compatibilizer, the crystallization characteristics of the two blend materials are affected by various aspects such as the magnitude of dispersion, the kind of compatibilizer, and the level of miscibility with either of the two blends, the mass of compatibilizer utilized and level of interface developed. Extensive study has been conducted in the crystallization behavior of distinct compatilibilized blends such as polypropylene and polyamide 6. It is identified that adding of various compatibilizers such as PP-g-MA extensively affects crystallization behavior of the blend (Krištofič & Ujhelyiová, 2012). The blending of the polymers is attained by adding some additives to the main polymer. Joint alterations utilize chemical altered agents which are added to the major polymer resulting to a blend system; the other polymer is added as an additive (Ozen, Kiziltas, Kiziltas, & Gardner, 2013). The development of blends from artificial commercial polymers is an easier method in comparison to the synthesis of distinct copolymers with the desired properties. The alteration of non-polar polypropylene aiming to enhance its properties is possible with specific amount of another blend additive (Salamone1996). The alteration of propylene by preparing a propylene/polyamide blend represents a basic methodology of modification of propylene properties. The process joins the thermo mechanical characteristics of PA with the easy feasibility of polyamide 6. The blend of incompatible polymers is mainly categorized by short spreading of phases, great interfacial tautness, and poor linkage (Salamone1996). The compatibilizer interrelates and enhances compatibilization during the compounding progression. It may as well alter the properties of the end product. Production of the Blend According to Kojima et al (1993), Polyamide 6 has superior mechanical strength characteristics but weak brittleness. Polypropylene on the other hand has poor mechanical strength but excellent resilience. Blends have been prepared with the two polymers and the mechanical properties of the blends vary depending on the percentage of each polymer used (Ozen, Kiziltas, Kiziltas & Gardner, 2013). During the blending process, polypropylene and polyamide 6 are utilized while in their granular state. The recognition of the molecular factors of the two raw materials is achieved by use of spectroscopic methodology (Krištofič & Ujhelyiová, 2012). Infrared Fourier transform is utilized to prove that the polymers utilized in the blending process are in reality polypropylene and polyamide 6. It is also utilized in the analyzing of the two samples after the blending process. The process of blending is carried out by use of electric mixer and the samples are obtained through injection. The physical characteristics which include both the melting point and melt flow of the raw materials are initially determined by use of plastometer and elecrothermal equipment. During the process of blending, the twin-screw extruder reactor primarily heats the polypropylene material into a low viscosity fluid (Salamone, 1996). Then crushed maleic anhydride in conjunction with organic peroxide pre-mixture is meted and added to the polypropylene fluid. As the PP-MAH-peroxide compound is transported in the reactor, grafting process occurs between the two materials resulting to a PP-g-MAH (Krištofič & Ujhelyiová, 2012). Following a fixed amount of reaction period, a devolatilization region is utilized in getting lead of any un-reacted MAH and peroxide offshoots. The amount of reaction time depends on screw geometry, transportation length, and screw speed. The devolatilization region is established in the twin-screw polymer reactor which under starve-fed setting by introducing reverse transport screw rudiments on both sides of the devolatilization zone (Krištofič & Ujhelyiová, 2012).The rudiments lead to the creation of ‘melt-seals’ that allow introduction of a vacuum and the devolatilization of un-reacted materials to take place. Consequently, the PP-g-MAH polymer is transported downstream from the melt-seal. PA 6 is added by metering solid polymer particles into the twin-screw extruder reactor or by utilization of a side-stream extruder to add fluid PA 6 into the major reactor (Salamone, 1996). The second method is more recommended because the progression of melting PA 6 in the major reactor turns into a momentous heat-sink. The use of an additional extruder eradicates the necessity of energy requirements in the primary reactor to cater for the thawing of PA. The PP, PP-g-MAH and PA 6 blend is consequently moved down the reactor screws for a specific amount of time based on the factors considered in the previous reactor (Salamone, 1996). The amine end group of PA 6 reacts with MAH of the PP-g-MAH takes place. The condensation reaction results to formation of an amide moiety and a water molecule is released as a side-product (Ozen, Kiziltas, Kiziltas & Gardner, 2013). The molten polymer is a constituent of PP, PP-g-MAH, PP-g-PA, PA 6 and water. The viscous fluid goes into the last devolatilization section where the water and other by-products are eliminated. The polymer produce which undergoes the process of pelletization is a polymer merge of PP and PA 6 which is already compatibilized by the by-product PP-g-PA 6 copolymer. The level of MAH grafting, the quantity of PP-g-PA copolymer development are dependent on the amount of reacting materials added and the conditions of the reacting environment. Other usual compounding process which include; addition of additives and coloring agents is done at the twin-screw polymer reactor as the polymer is produced (Salamone, 1996). Diagram Showing the Production Process (Salamone, 1993, p. 7400) Mechanical Properties According to Djeddi and Ouibrahim (2014), the elasticity modulus is directly proportional with the PA 6 in the PP medium for the raw samples, but it is inversely proportional with the polymer blend. (Djeddi & Ouibrahim, 2014, p. 2) For stress-strain behavior, the polymer blend with 100% PP virgin polymer has excellent mechanical properties in comparison the 100 % which has fragile mechanical properties (Zwijnenburg, 2012). Graph Showing Stress-Strain Behavior of PA 6/ PP Blend (Djeddi & Ouibrahim, 2014, p. 3) The elongation of rupture is directly proportional to the amount of PA in the PP medium and the same applies for the polymer blend. The ruture stress gets stable at 50% for the PA 6 virgin blend; however, at the rate of 100 % PA, the blend increses its resistant to rupture. Resilience increases as the rate of PP increases in the blend (Djeddi & Ouibrahim, 2014). PA gains ductility during the blending process which is due to the augmentation of the polydispersity indicator which restricts the level of crystallinity of the material. The ductility is revealed by making comparison of the SEM micrographs. Polymers are blended so as to improve their mechanical characteristics (Morawetz, 2002). Originally, Polyamide 6 has superior mechanical strength characteristics but weak brittleness (Kojima et al., 1993). Polypropylene on the other hand has poor mechanical strength but excellent resilience (Zwijnenburg, 2012). The characteristics of the blend vary depending on the rate of each of the two materials used. Compatibilizers are utilized in the process of blending so as to improve the compatibility between the two polymers. References Djeddi, F., & Ouibrahim, A. (2014).Elaboration and characterization of blends-Polyamide 6/6 with Polypropylene-and evolution of their mechanical properties with recycling.http://www.ummto.dz/IMG/pdf/Djeddi.pdf Nanofibrils from Nylon 6/Polypropylene-g-maleic anhydride/Polypropylene Blended Filaments.Iranian Polymer Journal, 20(5), 433-443.http://www.sid.ir/EN/VEWSSID/J_pdf/813201113109.pdf Gunatillake, P. A., & Adhikari, R. (2003). Biodegradable synthetic polymers for tissue engineering.Eur Cell Mater, 5(1), 1-16.http://www.ecmjournal.org/journal/papers/vol005/pdf/v005a01.pdf Huang, Z. M., Zhang, Y. Z., Kotaki, M., & Ramakrishna, S. (2003).A review on polymer nanofibers by electrospinning and their applications in nanocomposites. Composites science and technology, 63(15), 2223-2253. Kojima, Y., Usuki, A., Kawasumi, M., Okada, A., Fukushima, Y., Kurauchi, T., & Kamigaito, O. (1993).Mechanical properties of nylon 6-clay hybrid. Journal of Materials Research, 8(05), 1185-1189. Krištofič, M., &Ujhelyiová, A. (2012).Compatibilisation of PP/PA Blends.FIBRES & TEXTILES in Eastern Europe, 20(4), 93.http://fibtex.lodz.pl/pliki/Fibtex_%28jpl0xsep7o4raxpn%29.pdf Morawetz, H. (2002). Polymers: The Origins And Growth Of A Science. Mineola (N.Y.): Dover publishers. Ozen, E., Kiziltas, A., Kiziltas, E. E., & Gardner, D. J. (2013). Natural fiber blend—nylon 6 composites. Polymer Composites, 34(4), 544-553. Salamone J. C. (1996). Polymeric Materials Encyclopedia, Twelve Volume Set. Boca Raton, Florida. CRC Press. http://books.google.co.ke/books?id=g3vPjBl0wHEC&pg=PA7401&lpg=PA7401&dq=process+of+blending+two+polymers+PA+and+PP&source=bl&ots=GoiTQtOD9T&sig=PNANqJkUR71b8HOoF4hoztGe8is&hl=en&sa=X&ei=C69sVLyOEYrkaoiSgvgK&redir_esc=y#v=onepage&q=process%20of%20blending%20two%20polymers%20PA%20and%20PP&f=false Zwijnenburg, M. A. (2012). Elucidating the Microscopic Origin of the Unique Optical Properties of Polypyrene. The Journal of Physical Chemistry C, 116(38), 20191-20198. Read More

The major dissimilarity between the two methods is that; in the chain growth polymerization, polymers are joined to the chain one at a time. On the other hand, step-growth polymerization, the monomers may join to each other openly. The artificial polymerization methods may utilize catalysts or not (Morawetz, 2002).The natural occurring polymers are of three categories which include; polysaccharides, polynucleotides, and polysaccharides. Naturally, the process of synthesis may be mediated by enzymes.

For instance, the process of DNA synthesis involves various enzyme mediated steps. Majority of the commercial polymers are obtained through chemical alteration of the naturally occurring polymers. An example of chemical modification is the process of reacting nitric acid with cellulose in the development of nitrocellulose. Polymers may be modified in various ways such as cross-linking and oxidation (Morawetz, 2002). Polymer properties are of two categories and the most common property is the individuality of the polymer monomer.

The other property is referred to as the microstructure which is the prearrangement of the monomers within the polymer at the gauge of a sole chain. The major properties play a significant role in the determination of bulk physical characteristics of the polymer which designates the behavior of unremitting macroscopic material (Huang, Zhang, Kotaki & Ramakrishna, 2003). At the nano-scale, chemical characteristics explain the interaction of the chains through distinct physical conditions. The macro-scale explains the interaction of the bulk polymer with other chemicals and solvents.

Polypropylene Polypropylene refers to a thermoplastic polymer utilized in various applications which include packaging, stationery, labelling, textiles, and renewable vessels. Also, it is utilized in the automotive equipment ad loudspeakers. Additionally, there is a polymer developed from monomer propylene (Fallahi, Barmar & Kish, 2011). The polymer is craggy and extraordinarily resists to numerous solvents, basic, and acidic solutions. Majority of the marketable Polypropylene is isotactic and has a moderate density.

It is generally hard and elastic especially after copolymerization with ethylene. This makes Polypropylene appropriate for use in engineering plastics together with materials such as ABS. Polypropylene is practically economical and can be produced in the translucent form (Kojima et al., 1993). However, it does not appear transparent ay acrylic and other plastics. In most cases, it is opaque or colored by use of pigmentation. Polypropylene properly resists fatigue and it melts at a range of temperatures.

Therefore, the melting is obtained by determination of the highest temperature from a differential scanning calorimeter. Isotactic polypropylene melts at a temperature of 171oC whereas commercial isotactic polypropylene melts at a range of temperature ranging from 160o C to 166o C reliant on the atacticity and crystallinity (Kojima et al., 1993). The melt flow rate refers to a degree of molecular massof polypropylene. This degree assists in the determination of the movement of the molten substance as a raw material in the course of processing.

The effect strength reduces with an increase in the melt flow. Polypropylene is of three categories which include; block copolymer, homopolymer, and random copolymer (Zwijnenburg, 2012). The comonomer is generally used in conjunction with ethylene. Ethylene- polypropylene rubber joined to polypropylene homopolymer raises its low temperature impact power. According to Zwijnenburg (2012), Polypropylene is liable to chain degradation from high temperature treatment and Ultra-Violetradiation. Oxidation normally takes place at the tertiary carbon molecule in each recurrent unit.

The process leads to the formation of a free radical which reacts with another oxygen molecule trailed by chain scission to form aldehydes and carboxylic acids. In exterior applications, it is seen as chains of fine fissure that deepen and get severe as the exposure time elapses (Morawetz, 2002).

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