Polyester TPUs

Post-curing effect In Table 9.12 it can be seen that the use of the mixed chain-extender system Dianol 22 + EDO with both PPDI and CHDI gives very strong polyurethanes (cf. mixes 1 and 2) with tensile strengths around 38 5 MPa, whilst post-curing the CHDI-based TPU results in a further increase to 43 MPa and reduces compression set from 56 to 40% (at 100°C). A comparative postcuring experiment with a PPDI-based TPU gave no real improvement in these properties (refer to compounds 4 and 5). 

PROPERTIES OF THERMOPLASTIC POLYURETHANES BASED ON POLYCAPROLACTONE (POLYESTER) OF 2000 MOLECULAR WEIGHT 

Shore A strength at break modulus modulus (70 hat 25% resilience (MPa) (%) (MPa) (MPa) strain) 

Note 15 was a soft, transparent, very flexible polyurethane with high hysteresis and set. 

16 was a high hysteresis, slow recovery, elastomer with a low set. 

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Polyester TPUs are compatible with PVC and other polar plastics. Offering value in the form of enhanced properties, they are unaffected by oils and chemicals, provide excellent abrasion resistance, offer a good balance of physical properties, and are perfect for use in polyblends. 

TPUs are polar materials and are therefore resistant to nonpolar organic fluids such as oils, fuels, and greases, but they are readily attacked and even dissolved by polar organic fluids such as dimethylformamide and dimethylsulfoxide. TPUs behave like copolyester TPEs toward water and aqueous solutions, being resistant to these media except at very high or low pH. Polyether TPUs are more resistant to such hydrolytic degradation than are the polyester TPUs. 

The polyblends are polyester TPUs blended with ABS, SAN, PC, nylon, PVC, and other thermoplastics for injection molding and extrusion. A 10 to 20% loading into PVC compositions can increase mechanical properties 30 to 40%. Although the elastomeric TPUs are inherently flexible, plasticizers may be recommended, for example, in films. 

In addition, polyester polyols are made by the reaction of caprolactone with diols. Poly(caprolactone diols) are used in the manufacture of thermoplastic polyurethane elastomers with improved hydrolytic stabiHty (22). The hydrolytic stabiHty of the poly(caprolactone diol)-derived TPUs is comparable to TPUs based on the more expensive long-chain diol adipates (23). Polyether/polyester polyol hybrids are synthesized from low molecular weight polyester diols, which are extended with propylene oxide. 

TPU is usually made from hydroxyl-terminated polyether or polyester diols, diisocyanates, and bifunctional chain extenders. Since the composition, the synthetic method, molecular weight, and its distribution are all changeable, there are numerous types of TPUs available, and their prices and properties vary significantly. 

Both polyester- and polyether-based TPU could be used to blend with PVC, although the former constitutes the majority of the commercial products. All of the blends should meet the following requirements (I) they must have good or relatively good compatibility with PVC, (2) their processing temperature should be close to or lower than that of PVC, (3) they have to meet the specific requirements of the products, for example, TPUs used for medical purposes should be colorless (if possible), transparent, nontoxic, and able to be sterilized, and (4) they should not be expensive. 

Several commercial products of PVC/TPU blends are available. The BF Goodrich Chemical Group has a PVC/ TPU blend based on their Estane series TPUs. For example, their Estane 54620, a polyester-based TPU with a °ShA 85 hardness, shows excellent compatibility with flexible PVC. The blends are produced by mixing PVC, TPU, plasticizer, stabilizer, and lubricant in a twin-screw extruder. These polymeric blends show intermediate mechanical properties between PVC and TPU. 

TPUs are handicapped by a lower elasticity than conventional rubbers, the more so the higher the hardness certain risks of creep, relaxation and permanent set, the more so the higher the temperature higher cost than TPOs risks of hydrolysis especially for the polyester types UV exposure yellowing incompatibility between certain polyester and polyether grades aromatic and chlorinated hydrocarbon behaviour limited thermal behaviour density inherent flammability, but FR grades are marketed risks of fume toxicity in the event of fire. 

As with other block copolymers, the nature of the soft segments determines the elastic behavior and low-temperature performance. TPUs based on polyester soft blocks have excellent resistance to nonpolar fluids and high tear strength and abrasion resistance. Those based on polyether soft blocks have excellent resistance (low heat buildup, or hysteresis), thermal stability, and hydrolytic stability. 

There are three main chemical classes of TPUs polyester, polyether, and a smaller class known as polycaprolactone [3]. 

Poly ether TPUs are slightly lower in specific gravity than polyester and polycaprolactone grades. They offer low temperature flexibility and good abrasion and tear resilience. They are also durable against microbial attack and... 

Polycaprolactone TPUs have the inherent toughness and resistance of polyester-based TPUs combined with low temperature performance and a relatively high resistance to hydrolysis. They are an ideal raw material for hydraulic and pneumatic seals. 

The polyester-based TPUs have the following characteristic features ... 

Polyester urediane rubber Polyedier urediane rubber Millable polyurethane rubber (not thermoplastic polyurethane elastomers (TPUs) AU EU... 

Thermoplastic Polyurethanes (TPUs). The first commercial TPEs were the TPUs, which have the same block copolymer morphology as do the COPs. Their general structure is -A-B-A-B-, where A represents a hard crystalline block derived by chain extension of a diisocyanate with a glycol. The soft block, represented by B, can be derived from either a polyester or a polyether. Typical TPU structures, both polyester and polyether types, are represented here ... 

The polyester-type thermoset polyurethanes were commercialized in 1942, and the linear thermoplastic ones (TPU) 10 years later. Polyester-type TPUs, Texiit resins for extrusion and injection molding, were introduced in 1961, whereas polyether-type, Roylar , in 1971. Owing to great diversity of the ingredients, the TPU performance can be readily modified. For this reason, as well as because of the cost, TPUs are seldom blended. Their use can be divided into three groups (i) blends with POM, (ii) blends in which TPU is used as a compatibilizer and impact modifier, and (iii) others. 

The two principal types of TPUs are poly ether and polyester. Polyethers have good low-temperature properties and resistance to fungi polyesters have good resistance to fuel, oil, and hydrocarbon solvents. 

It is known that the potential monomers or pol5uner building blocks should have at least one (in the case of addition polymerization) or two double bonds in their structure (in the case of condensation pol5nnerization) to get thermoplastic materials. Therefore, triglycerides should be modified of fimctionalized before pol5nnerization. Nevertheless, there are some examples of thermoplastic biomaterials obtained from naturally functionalized castor oil with homogeneous composition and acceptable polymerization yields. The main thermoplastic materials already synthesized from vegetable oils are thermoplastic polyurethanes (TPUs), polyamides (PA), thermoplastic polyesters, polyesteramides and polyanhydrides. 

Biodegradable TPUs biodegradable polyurethanes are typically prepared from polyester polyols, aliphatic diisocyanates and chain extenders Tatai, L Moore, T G / dhikari, R Malherbe, F Jayasekara, R Griffiths, 1 Gunatillake, PA, Biomaterials, 28,5407-17, 2007. 

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