Solved: The tensile strength and number-average molecular

From the stressstrain data for poly(methyl methacrylate) shown in Figure 15.3, determine the modulus of elasticity and tensile strength at room temperature [20C (68F)], and compare these values with those given in Table 15.1.

Compute the elastic moduli for the following polymers, whose stressstrain behaviors can be observed in the Tensile Tests module of Virtual Materials Science and Engineering (VMSE): (a) high-density polyethylene (b) nylon (c) phenol-formaldehyde (Bakelite) How do these values compare with those presented in Table 15.1 for the same polymers?

For the nylon polymer whose stressstrain behavior can be observed in the Tensile Tests module of Virtual Materials Science and Engineering (VMSE), determine the following: (a) The yield strength (b) The approximate ductility, in percent elongation How do these values compare with those for the nylon material presented in Table 15.1?

For the phenol-formaldehyde (Bakelite) polymer whose stressstrain behavior can be observed in the Tensile Tests module of Virtual Materials Science and Engineering (VMSE), determine the following: (a) The tensile strength (b) The approximate ductility, in percent elongation How do these values compare with those for the phenol-formaldehyde material presented in Table 15.1?

In your own words, briefly describe the phenomenon of viscoelasticity.

For some viscoelastic polymers that are subjected to stress relaxation tests, the stress decays with time according to s(t) = s(0) expa - t t b (15.10) where s(t) and s(0) represent the time-dependent and initial (i.e., time  0) stresses, respectively, and t and t denote elapsed time and the relaxation time, respectively; t is a time-independent constant characteristic of the material. A specimen of a viscoelastic polymer whose stress relaxation obeys Equation 15.10 was suddenly pulled in tension to a measured strain of 0.5; the stress necessary to maintain this constant strain was measured as a function of time. Determine Er(10) for this material if the initial stress level was 3.5 MPa (500 psi), which dropped to 0.5 MPa (70 psi) after 30 s.

In Figure 15.28, the logarithm of Er(t) versus the logarithm of time is plotted for PMMA at a variety of temperatures. Plot logEr(10) versus temperature and then estimate its Tg.

On the basis of the curves in Figure 15.5, sketch schematic straintime plots for the following polystyrene materials at the specified temperatures: (a) Crystalline at 70C (b) Amorphous at 180C (c) Crosslinked at 180C (d) Amorphous at 100C 15

(a) Contrast the manner in which stress relaxation and viscoelastic creep tests are conducted. (b) For each of these tests, cite the experimental parameter of interest and how it is determined.

Make two schematic plots of the logarithm of relaxation modulus versus temperature for an amorphous polymer (curve C in Figure 15.8). (a) On one of these plots, demonstrate how the behavior changes with increasing molecular weight. (b) On the other plot, indicate the change in behavior with increasing crosslinking.

For thermoplastic polymers, cite five factors that favor brittle fracture.

(a) Compare the fatigue limits for PMMA (Figure 15.11) and the 1045 steel alloy for which fatigue data are given in Figure 8.20. (b) Compare the fatigue strengths at 106 cycles for nylon 6 (Figure 15.11) and 2014-T6 aluminum (Figure 8.20).

In your own words, describe the mechanisms by which semicrystalline polymers (a) elastically deform (b) plastically deform (c) by which elastomers elastically deform

Briefly explain how each of the following influences the tensile modulus of a semicrystalline polymer and why: (a) molecular weight (b) degree of crystallinity (c) deformation by drawing (d) annealing of an undeformed material (e) annealing of a drawn material

Briefly explain how each of the following influences the tensile or yield strength of a semicrystalline polymer and why: (a) molecular weight (b) degree of crystallinity (c) deformation by drawing (d) annealing of an undeformed material

Normal butane and isobutane have boiling temperatures of 0.5C and 12.3C (31.1F and 9.9F), respectively. Briefly explain this behavior on the basis of their molecular structures, as presented in Section 14.2. 15

The tensile strength and number-average molecular weight for two poly(methyl methacrylate) materials are as follows: Tensile Number-Average Strength (MPa) Molecular Weight (g/mol) 50 30,000 150 50,000 Estimate the tensile strength at a number-average molecular weight of 40,000 g/mol.

The tensile strength and number-average molecular weight for two polyethylene materials are as follows: Tensile Number-Average Strength (MPa) Molecular Weight (g/mol) 90 20,000 180 40,000 Estimate the number-average molecular weight that is required to give a tensile strength of 140 MPa.

For each of the following pairs of polymers, do the following: (1) State whether it is possible to decide whether one polymer has a higher tensile modulus than the other; (2) if this is possible, note which has the higher tensile modulus and cite the reason(s) for your choice; and (3) if it is not possible to decide, state why. (a) Branched and atactic poly(vinyl chloride) with a weight-average molecular weight of 100,000 g/mol; linear and isotactic poly(vinyl chloride) having a weight-average molecular weight of 75,000 g/mol (b) Random styrene-butadiene copolymer with 5% of possible sites crosslinked; block styrenebutadiene copolymer with 10% of possible sites crosslinked (c) Branched polyethylene with a number-average molecular weight of 100,000 g/mol; atactic polypropylene with a number-average molecular weight of 150,000 g/mol

For each of the following pairs of polymers, do the following: (1) State whether it is possible to decide whether one polymer has a higher tensile strength than the other; (2) if this is possible, note which has the higher tensile strength and cite the reason(s) for your choice; and (3) if it is not possible to decide, state why. (a) Linear and isotactic poly(vinyl chloride) with a weight-average molecular weight of 100,000 g/mol; branched and atactic poly(vinyl chloride) having a weight-average molecular weight of 75,000 g/mol (b) Graft acrylonitrilebutadiene copolymer with 10% of possible sites crosslinked; alternating acrylonitrilebutadiene copolymer with 5% of possible sites crosslinked (c) Network polyester; lightly branched polytetrafluoroethylene

Would you expect the tensile strength of polychlorotrifluoroethylene to be greater than, the same as, or less than that of a polytetrafluoroethylene specimen having the same molecular weight and degree of crystallinity? Why?

For each of the following pairs of polymers, plot and label schematic stressstrain curves on the same graph [i.e., make separate plots for parts (a) to (c)]. (a) Polyisoprene having a number-average molecular weight of 100,000 g/mol and 10% of available sites crosslinked; polyisoprene having a numberaverage molecular weight of 100,000 g/mol and 20% of available sites crosslinked (b) Syndiotactic polypropylene having a weightaverage molecular weight of 100,000 g/mol; atactic polypropylene having a weight-average molecular weight of 75,000 g/mol (c) Branched polyethylene having a numberaverage molecular weight of 90,000 g/mol; heavily crosslinked polyethylene having a number-average molecular weight of 90,000 g/mol

List the two molecular characteristics that are essential for elastomers.

Which of the following would you expect to be elastomers and which thermosetting polymers at room temperature? Justify each choice. (a) Linear and highly crystalline polyethylene (b) Phenol-formaldehyde (c) Heavily crosslinked polyisoprene having a glass transition temperature of 50C (122F) (d) Lightly crosslinked polyisoprene having a glass transition temperature of 60C (76F) (e) Linear and partially amorphous poly(vinyl chloride)

Fifteen kilograms of polychloroprene is vulcanized with 5.2 kg of sulfur. What fraction of the possible crosslink sites is bonded to sulfur crosslinks, assuming that, on the average, 5.5 sulfur atoms participate in each crosslink?

Compute the weight percent sulfur that must be added to completely crosslink an alternating acrylonitrilebutadiene copolymer, assuming that four sulfur atoms participate in each crosslink.

The vulcanization of polyisoprene is accomplished with sulfur atoms according to Equation 15.4. If 45.3 wt% sulfur is combined with polyisoprene, how many crosslinks will be associated with each isoprene repeat unit if it is assumed that, on the average, five sulfur atoms participate in each crosslink?

For the vulcanization of polyisoprene, compute the weight percent of sulfur that must be added to ensure that 10% of possible sites will be crosslinked; assume that, on the average, 3.5 sulfur atoms are associated with each crosslink.

In a manner similar to Equation 15.4, demonstrate how vulcanization may occur in a chloroprene rubber

Determine values for the constants n and k (Equation 10.17) for the crystallization of polypropylene (Figure 15.17) at 150C.

Which of the following polymers would be suitable for the fabrication of cups to contain hot coffee: polyethylene, polypropylene, poly(vinyl chloride), PET polyester, and polycarbonate. Why?

Of the polymers listed in Table 15.2, which polymer(s) would be best suited for use as ice cube trays? Why?

For each of the following pairs of polymers, plot and label schematic specific volume-versustemperature curves on the same graph [i.e., make separate plots for parts (a) to (c)]. (a) Linear polyethylene with a weight-average molecular weight of 75,000 g/mol; branched polyethylene with a weight-average molecular weight of 50,000 g/mol (b) Spherulitic poly(vinyl chloride) of 50% crystallinity and having a degree of polymerization of 5000; spherulitic polypropylene of 50% crystallinity and degree of polymerization of 10,000 (c) Totally amorphous polystyrene having a degree of polymerization of 7000; totally amorphous polypropylene having a degree of polymerization of 7000

For each of the following pairs of polymers do the following: (1) State whether it is possible to determine whether one polymer has a higher melting temperature than the other; (2) if it is possible, note which has the higher melting temperature and then cite reason(s) for your choice; and (3) if it is not possible to decide, then state why. (a) Branched polyethylene having a numberaverage molecular weight of 850,000 g/mol; linear polyethylene having a number-average molecular weight of 850,000 g/mol (b) Polytetrafluoroethylene having a density of 2.14 g/cm3 and a weight-average molecular weight of 600,000 g/mol; PTFE having a density of 2.20 g/cm3 and a weight-average molecular weight of 600,000 g/mol (c) Linear and syndiotactic poly(vinyl chloride) having a number-average molecular weight of 500,000 g/mol; linear polyethylene having a numberaverage molecular weight of 225,000 g/mol (d) Linear and syndiotactic polypropylene having a weight-average molecular weight of 500,000 g/mol; linear and atactic polypropylene having a weight-average molecular weight of 750,000 g/mol

Make a schematic plot showing how the modulus of elasticity of an amorphous polymer depends on the glass transition temperature. Assume that molecular weight is held constant.

Briefly explain the difference in molecular chemistry between silicone polymers and other polymeric materials

List two important characteristics for polymers that are to be used in fiber applications.

Cite five important characteristics for polymers that are to be used in thin-film applications.

Cite the primary differences between addition and condensation polymerization techniques.

(a) How much ethylene glycol must be added to 20.0 kg of dimethyl terephthalate to produce a linear chain structure of poly(ethylene terephthalate) according to Equations 15.9? (b) What is the mass of the resulting polymer?

Nylon 6,6 may be formed by means of a condensation polymerization reaction in which hexamethylene diamine [NH2(CH2)6NH2] and adipic acid react with one another with the formation of water as a by-product. What masses of hexamethylene diamine and adipic acid are necessary to yield 20 kg of completely linear nylon 6,6? (Note: The chemical equation for this reaction is the answer to Concept Check 15.12.)

What is the distinction between dye and pigment colorants?

Cite four factors that determine what fabrication technique is used to form polymeric materials.

Contrast compression, injection, and transfer molding techniques that are used to form plastic materials.

must fiber materials that are melt-spun and then drawn be thermoplastic? Cite two reasons.

Which of the following polyethylene thin films would have the better mechanical characteristics? (1) Those formed by blowing. (2) Those formed by extrusion and then rolled. Why?

(a) List several advantages and disadvantages of using transparent polymeric materials for eyeglass lenses.(b) Cite four properties (in addition to being transparent) that are important for this application. (c) Note three polymers that may be candidates for eyeglass lenses, and then tabulate values of the properties noted in part (b) for these three materials

Write an essay on polymeric materials that are used in the packaging of food products and drinks. Include a list of the general requisite characteristics of materials that are used for these applications. Now, cite a specific material that is used for each of three different container types and the rationale for each choice.

Write an essay on the replacement of metallic automobile components by polymers and composite materials. Address the following issues: (1) Which automotive components (e.g., crankshaft) now use polymers and/or composites? (2) Specifically what materials (e.g., high-density polyethylene) are now being used? (3) What are the reasons for these replacements?

Amorphous thermoplastics are formed above their (A) glass transition temperatures (B) softening points (C) melting temperatures (D) none of the above