Level temperature, impact

The particle size of the dispersed phase depends upon the viscosity of the elastomer-monomer solution. Preferably the molecular weight of the polybutadiene elastomer should be around 2 x 10 and should have reasonable branching to reduce cold flow. Furthermore, the microstructure of the elastomer provides an important contribution toward the low-temperature impact behavior of the final product. It should also be emphasized that the use of EPDM rubber [136] or acrylate rubber [137] may provide improved weatherability. It has been observed that with an increase in agitator speed the mean diameter of the dispersed phase (D) decreases, which subsequently levels out at high shear [138-141]. However, reagglomeration may occur in the case of bulk... 

It is obvious from these data that CTBN (the carboxyl terminated butadiene-acrylonitrile copolymer) is the most effective modifier, and therefore it was selected for further study. As the concentration of the elastomer was increased to levels up to 100 parts, the impact also increased. The data in Table II show that the room temperature impact of ERL-4221 increased from 40 inch-lbs to greater than 320 inch-lbs by adding 100 phr or 33 wt % of CTBN. At very low temperatures ( —160°F) the impact of the system modified with 60 parts, or 23 wt %, of CTBN was 120 inch-lbs. These impact improvements appear to be directly proportional to the concentration of the elastomer modifier. 

A variation in the ratio of g-PE to g-EPDM causes a marked variation in the impact strength of PA blends. Eor the two types of blends, a maximum was observed at 50-70 wt% of g-EPDM in g-PE/g-EPDM blends. A rather high level of impact strength is found at negative temperatures (about 25 kJ m at —40°C and 18 kJ m at -60°C, Pig. 18.8b). 

Kinetics Studies After determining tlie parameter witli the highest effect upon Sotolon concentration in port wines, attempts were made to establish a matliematical model, which reflects tlie impact of oxygen level, temperature as well as the time of storage, on the rate of formation of Sotolon. 

Stiffness plus low-temperature impact With their use growing at about 10% per year, TPOs can provide varying levels of impact resistance and varying flexural modulus values and are tailored for particular applications, from the most extreme exterior bumper fascia parts to softer interior components (Chapters 7 and 8). Other additives pair these properties with scratch-resistance (Chapter 17). 

General-purpose impact modification is a very low level of impact modification. It improves room temperature impact strength but does not take into account any requirements for low temperature (below 0°C) impact strength. For most of fliese types of apphcations, only low levels of impact modifier will be required (<10%). 

Low temperature impact strength is required for apphcations that require a certain level of low temperature flexibility and resistance to break. This is for example the case for many applications in the apphance area. For this purpose, modifier levels between 5 and 15% of mostly reactive modifiers will be necessary. Reactive modifiers can bond chemically to the base polymer. 

The specific composition of the TPO blend produced depends on the balance of flexural modulus (stiffness) and impact toughness (drop impact and notched Izod) properties needed to meet the target performance specifications. In the formulation of TPO blends, the polypropylene is used normally as the major component, i.e., as the matrix phase, to provide the needed rigidity and thermal stability, while the elastomer dispersion provides the low-temperature impact toughness. A minor amount of a mineral filler such as talc provides additional stiffness and dimensional stability to the TPO. Hence, the levels of elastomer and mineral filler modifiers are carefully adjusted to achieve the desired balance of properties in the TPO. 

A discussion of the ABS/PC blends comparing with other ABS blends may be found under the ABS blends section (Sect. 19.3.2). The properties of the ABS/PC blends, primarily the DTUL and impact strength, are determined by the ratio of ABS to polycarbonate. The morphology is also dictated by the blend ratio. In blends containing >50 % polycarbonate, the continuous phase is formed by the polycarbonate with ABS as the dispersed phase. The rubber particles are primarily located in the SAN phase. Typical properties of some of the commercial ABS/PC blends have already been discussed under the ABS blends section (Sect. 19.3.2) and illustrated in Tables 19.8, 19.9, and 19.28. The blends containing higher levels of polycarbonate exhibit better low-temperature impact strengths. 

Low levels of TPU have been blended with polyesters, such as polybutylene-terephthalate (PBT) and polyethleneterephthalate (PET). Blends of 10 to 30% TPU contribute to the toughness and low-temperature impact properties of PBT and PET [67]. 

The optimum level of hiphenol in the composition for improved low-temperature impact appears to fall in the range of 26 to 34 mol % (Fig. 14.16). The improved ductility of these copolymers appears to be related to a combination of the presence of biphenol-carbonate-rich microdomains (10 to 20 im) and the low rotational-energy barrier aroimd the biphenyl units in the polymer chain [175]. In addition to low-temperature ductility, the resins maintain a higher percentage of their notched Izod impact strength after heat-aging compared to standard BPA polycarbonate [176-182],... 

Ethylene vinyl acetate copolymer (EVA) is a low density polyethylene copolymer with excellent low temperature impact properties. The higher the level of vinyl acetate, the greater the flexibility of the material. Colorants, flame retardants, and foaming and antistatic agents may be added to polyethylene for specialty applications. Comparisons with other resins are given in Table 2. 

The process input variables (usually flows) affect the process state variables (usually pressure, level, temperature, concentration) which in turn have an impact on the measured process output such as a quality (for example viscosity). One should then ask oneself the question what part of the process do I want to model the relationship between the process inputs and the quality variable or the relationship between the state variables and the measured quality variable or the relationship between the process inputs and the state variables It would not be logical to model the quality variable as a function of both the process inputs and the state variables. The latter exercise would be one that is not likely to be successful, since the process inputs affect the state variables and the state variables affect the process quality variable. Furthermore, the state variables are usually not mutually independent, for example temperature, pressure and composition. This means that a model that includes the process inputs as well as the state variables as additional inputs, models the effect of the true process inputs multiple times. Therefore a proper selection of the inputs and output(s) of the model is very important. 

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