Processing stability of polypropylene

Mechanisms of Degradation Inhibitors. The degradation mechanisms described above have no little effect on end-use stability and processing stability of polypropylene. Indeed, without stabilizers and antioxidants to inhibit such degradation reactions, polypropylene would have limited usefulness as a structural plastic if any usefulness at all. 

Figure 1. Processing stability of polypropylene, PPP vs. aryl phosphite...

Figure 2. Processing stability of polypropylene in a Brabender torque...

Figure 3. Processing stability of polypropylene on large-scale equipment...

Some of the test methods being used to measure the processing stability of polypropylene include melt flow drift measurements at elevated temperatures using an extrusion plastometer (melt indexer), melt viscosity retention measurements using a torque rheometer, retention of melt flow after repeated extrusions, and injection molded spiral test measured by the flow in inches at various temperatures and the retention of melt flow of the injected spirals. The nine commercial resins were evaluated by these methods. 

Piperazine HALS 2 has a positive effect on the processing stability of polypropylene when used in conjunction with a phenolic antioxidant ... 

Table 3.1 Comparison of processing stabilization of polypropylene stabilized with 0.1% of a classic blend system (0.1 % Irganox B 215 (phenol (Irganox 1010) + phosphite (Irgafos 168) 1 2)) and with 0.07% of a lactone-based product (0.07% Irganox HP 2215 (85% phenol/phosphite blend (Irganox B 215)) + 15% lactone (HP 136)) [539]...

Johnson B, Keck-Antoine K, Dejolier B, Allen N, Ortuoste N, Edge M. Impact of improved phosphite hydrolytic stability on the processing stabilization of polypropylene. J Vinyl Ad-dit Technol 2005 11 (4) 136 2. 

Pauquet JR. Breakthrough chemistry for processing stabilization of polypropylene. J. Macromol Sci Pure Appl Chem... 

A number of ortho hindered alkyl-substituted phenyl phosphites and phosphonites were found to be effective process stabilizers for polypropylene and high density polyethylene combining more effective stabilization activity at high temperatures with good storage stability at relatively elevated humidity and ambient temperature, as well as resistance to discoloration. 

Non-discoloring, sulfur containing phenolic antioxidant and stabilizer that provides long-term heat stability by preventing thermo-oxidative degradation. Used for the process stabilization of polyethylene wire and cable resins for polyethylene during extruder compounding. Can also be applied in styrenic polymers, polypropylene, elastomers such as EPDM and SBR and for carboxylated SBR latex, polybutadiene rubber and polyisopropene rubber. 

Polyolefins - An Arrhenius model has been developed for lifetime prediction of the light stability of polypropylene . Photooxidation processes in blends of polypropylene with poly(butylene terephthalate) (PBT) are complicated by the thermal sensitivity of the polypropylene and the screening effect of the terephthalate ester . This effect is shown in Scheme 1. 

Metal oxide semiconductor chemical sensors in combination with MDA have been shown to be useful to estimate the oxidative stability of polypropylene during processing instead of traditional melt flow index analysis (50). An array of sensors was used to receive a detailed analysis of volatiles. At quality measurements of different poly(butylene adipate)s the use of indicator products has been proven better than analyses of the decrease in molecular weight or mass loss for early degradation detection. Adipic acid, quantified using gas chromatography, was then used as the indicator product [51]. 

Photostabilization processes have not received much attention in the last year other than a multitude of review and specialist industrial articles. These include stabilization of polypropylene fibres, new stabilizer developments, sorting of stabilizers for polyethylene, trends in UV absorbers, hindered piperidines (hindered amine stabilizers (HAS)) for polyacrylics and urethanes, new stabilizers for polyolefins, enhanced service life applications, stabilizer mas-terbatches for polyester, stabilizers for UV cured acrylic overcoats for PVC, ° stabilization of clearcoats and various commercial packages. ... 

An alternative approach to uaiproving radiation stability has been through coupling the desirable processing properties of polypropylene with the radiation stability of polyethylene to form copolymers (polyallomers). Block polymers in which the chains comprise polymerized segments of each of the monomers are as amenable to processing as polypropylene while having better clarity and radiation stability. 

Table 5 Effect of processing history (190 °C) on the light stability of polypropylene films (300 nm) containing Irganox 1010 and hindered-piperidine additivies (0.1% each). Exposure unit microscal—lOOOW...

Typical processing stabilizers for polypropylene and butylated hydroxy-toluene (BHT) as the primary antioxidant and phosphates and phosphonates as secondary antioxidants. Examples of the latter that are commonly used are tetrakis-(2,4-di-terr-butyl-phenyl)-4-4 -bisphenylylenediphosphonite, distearyl-pentaerythrityl-diphosphonite, tris-(nonylphenyl)-phosphite, tris-(2,4-di-teft-butyl-phenyl)-phosphite and bis(2,4-di-ferr-butyl-phenyl)- pentaerythrityl-diphosphite. In commercial polypropylenes, phosphorous compounds are always used together with a sterically hindered phenol. The compounds are commonly added in concentrations between 0.05 and 0.25%. 

Recently, impact modifiers have been developed for plastics other than PVC. Polybutylene and other olefinic thermoplastic elastomers, for example, are being used to enhance the processability, toughness, and heat stability of polypropylene film. Hydroxy-terminated polyethers are being used to increase the impact resistance of polystyrene. Other conunon applications are polycarbonate, polyurethane, thermoplastic polyester, epoxy, and polysulfone. 

Zweifel H. Effect of stabilization of polypropylene during processing and its influence on long-term behavior under thermal stress. Polymer durability. Advances in chemistry series. 

Tochacek, J., Sedlaf, J. Effect of hydrolysability and stmctural features of phosphites on processing stability of isotactic polypropylene. Polym. Degrad. Stab. 41(2), 177-184 (1993) Zheng, K., Tang, H., Chen, Q., et al. Enzymatic synthesis of a polymeric antioxidant for efficient stabihzation of polypropylene. Polym. Degtad. Stab. 112, 27-34 (2015)... 

The lower thermal stability of natural fibers, up to 230°C, the thermal stability is only small, which limits the number of thermoplastics to be considered as matrix materials for natural fiber composites. Only those thermoplastics whose processing temperature does not exceed 230°C are usable for natural fiber reinforced composites. These are, most of all, polyolefines, such as polyethylene and polypropylene. Technical thermoplastics, such as poyamides, polyesters, and polycarbonates, require... 

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