1 Mechanical Properties
By adjusting the ratio of soft to hard segments, the hardness of polyether-ester elastomers can be varied across a wide range (Shore D 32–82); their elasticity and strength fall between those of rubber and plastics. Compared to other thermoplastic elastomers (TPEs), polyether-ester elastomers exhibit a higher modulus under low-strain conditions than other TPEs of equivalent hardness. When modulus is a critical design parameter, the use of polyether-ester elastomers allows for a reduction in the cross-sectional area of the finished product, thereby minimizing material consumption.
Polyether-ester elastomers possess exceptionally high tensile strength. Compared to thermoplastic polyurethanes (TPUs), polyether-ester elastomers exhibit significantly higher compressive and tensile moduli; consequently, when fabricating an identical component using polyether-ester elastomer and TPU of the same hardness, the former is capable of withstanding heavier loads. At temperatures above ambient, polyether-ester elastomers maintain a high flexural modulus, yet-unlike TPUs-they do not become excessively rigid at low temperatures. This makes them particularly well-suited for the manufacture of cantilever beams or torque-bearing components, and especially ideal for applications involving high-temperature environments. Polyether-ester elastomers demonstrate excellent low-temperature flexibility; their notched impact strength at low temperatures surpasses that of other TPEs, while their abrasion resistance is comparable to that of TPUs. Under low-strain conditions, polyether-ester elastomers exhibit superior fatigue resistance and minimal hysteresis loss. This characteristic, combined with their high elasticity, renders the material an ideal choice for applications involving repetitive cyclic loading, such as gears, rollers, flexible couplings, and belts.
2 Thermal Properties
Unless stabilized with antioxidants, polyether-ester thermoplastic elastomers undergo rapid degradation under various conditions-including exposure to water mist, ozone, and outdoor atmospheric environments. This degradation results in a reduction in viscosity and relative molecular weight, a decline in the material's elongation at break, and a deterioration in its instantaneous elastic recovery rate. This degradation reaction in polyether-esters proceeds via a free-radical mechanism, likely initiated by an oxidative attack on the carbon atoms adjacent to the ether oxygen atoms within the polymer backbone. During chain scission, formaldehyde is generated; this formaldehyde is subsequently oxidized to formic acid, which, in turn, catalyzes further chain scission. To enhance the resistance of polyether ester elastomers to oxidative degradation, appropriate stabilization methods should be employed; the added stabilizer system should comprise free radical scavengers, peroxide decomposers, and formaldehyde scavengers.
Polyether ester elastomers exhibit excellent thermal stability; generally, the higher the hardness, the better the heat resistance. Literature reports indicate that when subjected to continuous heating for 10 hours at 110°C and 140°C, polyether ester elastomers experience virtually no weight loss; even after heating for 10 hours at 160°C and 180°C, the weight loss remains minimal-only 0.05% and 0.1%, respectively. Isothermal thermogravimetric curves reveal that polyether ester elastomers begin to lose weight at 250°C, reaching a cumulative weight loss of 5% by 300°C, with significant weight loss occurring beyond 400°C. Consequently, polyether ester elastomers possess a very high maximum service temperature-with even higher limits for short-term exposure-and are capable of withstanding the paint-baking temperatures (150–160°C) typically encountered on automotive production lines. Furthermore, they exhibit minimal loss of mechanical properties across both high and low temperature extremes. When utilized at temperatures exceeding 120°C, the tensile strength of polyether ester elastomers significantly surpasses that of thermoplastic polyurethanes (TPU).
In addition, polyether ester elastomers demonstrate outstanding low-temperature performance. Their brittle point falls below -70°C; moreover, the lower the hardness, the greater the cold resistance, enabling most polyether ester elastomers to be utilized continuously for extended periods at temperatures as low as -40°C. Owing to the balanced performance exhibited by polyether ester elastomers across both high and low temperature ranges, they possess an exceptionally broad operating temperature window, capable of functioning effectively within the range of -70°C to 200°C.
3. Resistance to Chemical Media
Polyether ester elastomers possess excellent oil resistance and, at room temperature, can withstand most polar liquid chemical media (such as acids, bases, amines, and glycol compounds). However, they are susceptible to the effects of halogenated hydrocarbons (with the exception of Freons) and phenolic compounds. Generally, their chemical resistance improves in direct proportion to an increase in hardness. Polyether ester elastomers exhibit robust resistance to swelling and permeation when exposed to most organic solvents, fuels, and gases; specifically, their permeability to fuel is merely one-third to one-three-hundredth that of conventional oil-resistant rubbers, such as neoprene, chlorosulfonated polyethylene, and nitrile rubber. However, polyether ester elastomers exhibit relatively poor resistance to hot water; the addition of polycarbodiimide stabilizers can significantly enhance their hydrolysis resistance. It has been reported that introducing PEN or PCT into the PBT hard segments within the molecular chains of polyether ester elastomers yields materials with superior water and heat resistance.
4. Weather Resistance and Aging Resistance
Polyether ester elastomers demonstrate excellent chemical stability under a wide variety of conditions, including exposure to water mist, ozone, and outdoor atmospheric aging. As is the case with most TPEs, degradation occurs under the influence of ultraviolet (UV) light. Protective additives-including carbon black, various pigments, and other shielding materials-can be employed to mitigate this effect. The synergistic use of phenolic antioxidants and benzotriazole-type UV absorbers proves particularly effective in providing protection against UV- induced aging.
Oxidation induced by light and heat constitutes the two primary factors driving the degradation and aging of polyether ester elastomers. PEG-PBT copolyesters, in particular, exhibit poor resistance to both heat and light, rendering them highly susceptible to severe thermal-oxidative and photo-oxidative degradation. Elevated temperatures accelerate this degradation process. As aging progresses and molecular weight decreases, the material's elongation at break diminishes, and its instantaneous elastic recovery rate deteriorates.
Furthermore, polyether ester elastomers exhibit varying degrees of susceptibility to hydrolysis. When exposed to water, these elastomers undergo cross-linking reactions, resulting in an increased formation of gel-like substances. The inherent susceptibility of PEG-PBT copolyesters to hydrolytic degradation is precisely the property leveraged when utilizing them as biomaterial scaffolds for implantation within the human body. In aqueous environments, PEG-PBT copolyesters degrade via a hydrolytic mechanism: water molecules attack the ester linkages situated between the PEG and PBT segments, causing the polymer chains to cleave. The resulting degradation products consist of PEG and low-molecular-weight PBT fragments. The rate of degradation is influenced by various factors-including composition, temperature, pH level, and enzymatic activity-with higher PEG content, temperatures, and pH values generally leading to faster degradation rates. By precisely adjusting the relative proportions of the two constituent components, the degradation rate can be tailored to meet the specific requirements of diverse applications.
5. High Resilience
When TPEE materials are utilized in the manufacture of springs, they impart an exceptionally long service life to the components. This capability facilitates smooth and stable operation in applications such as railway systems, enabling trains to execute maneuvers-including starting, accelerating, decelerating, and stopping-with remarkable fluidity. Unlike metal springs, it does not rust, deteriorate under natural environmental conditions, or suffer from elastic fracture or loss of elasticity. Furthermore, when compared to rubber materials, it offers superior reusability while maintaining excellent elasticity.
6. Processing and Moldability
TPEE possesses excellent melt stability and ample thermoplasticity, resulting in excellent processability. It can be processed using a variety of thermoplastic processing techniques, such as extrusion, injection molding, blow molding, rotational molding, and melt casting. At low shear rates, the melt viscosity of TPEE is relatively insensitive to changes in shear rate; however, at high shear rates, the melt viscosity decreases as the shear rate increases. Since TPEE melts are highly sensitive to temperature-with melt viscosity varying by a factor of several to several dozen times within a temperature fluctuation range of just 10°C-temperature must be strictly controlled during the molding process.
To ensure that the resin's moisture content remains below 0.1%, it is necessary to pre-dry the material using a hot-air dryer (at 80–120°C for 6–8 hours) prior to processing.
1. Extrusion Molding
Using standard plastic extruders, TPEE can be extruded into various forms such as sheets, tubes, rods, and wire jacketing. A general-purpose, gradually deepening screw design is typically employed, featuring a length-to-diameter (L/D) ratio of ≥ 24:1 and a compression ratio of (2.7–4):1.
2. Injection Molding
Injection molding techniques allow for the production of articles in a wide variety of shapes and sizes. Reciprocating-screw injection machines are preferred for this application, as they produce a melt with highly uniform and consistent temperature distribution. The screw channel depth should follow a gradual profile; a compression ratio of 3.0–3.5 is recommended, along with a screw L/D ratio of (18–24):1. Injection pressures typically range from 80 to 120 MPa, utilizing a slow-to-medium injection speed.
3. Blow Molding
Blow molding applications require resins that exhibit high melt viscosity and melt strength. By applying chemical chain-extension techniques during polymer extrusion-specifically by incorporating special functional segments into the TPEE molecular chains-it is possible to produce high-viscosity TPEE grades capable of meeting the requirements for blow molding large, specialized components (such as engine air intake ducts).
4. Other Molding Processes
TPEE is also suitable for processes such as rotational molding and melt casting. For instance, rotational molding can be used to manufacture items such as balls and small tubeless tires. Melt casting, on the other hand, offers the advantages of low processing costs and excellent dimensional stability in the finished products.
