338 Appendix:Test 10.(4%)Polyvinyl chloride is stiffer than polyethylene.Explain the scientific origin of this observation.Note that the mer of polyethylene is HH -C-C— HH while the mer of polyvinyl chloride is the same as this except that one for the four hydrogen atoms has been replaced with a chlorine atom 11.(4%)What are the main problems with the method of self-healing involving microcapsules of a monomer? 12.(4%)Describe an effective method of improving the vibration damping ability of a continuous carbon fiber polymer-matrix composite. 13.(4%)Why does the time spent below the melting temperature prior to bonding affect the quality of the bond for polyphenylene sulfide(PPS)? 14.(4%)Why is aluminum foil sufficiently temperature resistant that it can be used in cooking? 15.(4%)Why does corrosion tend to occur in a fastened metal joint? 16.(4%)Why does sand blasting help to improve the corrosion resistance of steel rebars? Void content (Vol..‰%) 25 (a) (b) 15 00.05 0.10.150.2025030.35 Latex/cement ratio Figure A.2.Effect of the latex/cement ratio on the air void content of cement paste:a with 0.53 vol%carbon fibers;b with no fibers338 Appendix: Test 10. (4%) Polyvinyl chloride is stiffer than polyethylene. Explain the scientific origin of this observation. Note that the mer of polyethylene is H H C C H H while the mer of polyvinyl chloride is the same as this except that one for the four hydrogen atoms has been replaced with a chlorine atom. 11. (4%) What are the main problems with the method of self-healing involving microcapsules of a monomer? 12. (4%) Describe an effective method of improving the vibration damping ability of a continuous carbon fiber polymer-matrix composite. 13. (4%) Why does the time spent below the melting temperature prior to bonding affect the quality of the bond for polyphenylene sulfide (PPS)? 14. (4%) Why is aluminum foil sufficiently temperature resistant that it can be used in cooking? 15. (4%) Why does corrosion tend to occur in a fastened metal joint? 16. (4%) Why does sand blasting help to improve the corrosion resistance of steel rebars? Figure A.2. Effect of the latex/cement ratio on the air void content of cement paste: awith 0.53vol% carbon fibers; bwith no fibers