exam3spring2004

# Exam3spring2004 - ENSC 3313 Spring 2004 TEST 3 KEY Name Answer all 10 questions show all work 2points each 1 How many kg of S are needed to cross

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1 ENSC 3313, Spring 2004 TEST 3 - KEY Name_________________________ Answer all 10 questions, show all work, 2points each 1. How many kg of S are needed to cross link 5% of the sites in 1000 kg of polybutadiene, (C 4 H 6 ) n , presuming the S is 90% efficient. The amu are H = 1, C = 12, S = 32. Note: 2 crosslink sites per monomer. The mer weight is: (4 × 12+6)=54 g/mol Number of mers is: 1000 × 10 3 /54 = 18518 mol Each mer has 2 cross link sites and each S can crosslink 2 sites so for 5% cross-linking, need 925 mol S But, S is only 90% efficient so need 1028.8 mol of S Convert to mass. Need 32.9 kg. 2. a) “Polymers have two characteristic temperatures.” Explain! The melting temperature and the glass transition temperature define the processing and utilization range of the polymer. b) Both temperatures are lower for LDPE than HDPE. Why? LDPE is branched so it less crystalline, so less well packed and less rigid, so T g and T m are lower. c) For most practical purposes, polyvinyl chloride (PVC) has but one characteristic temperature. Tell! It does not crystallize, so does not have a T m . d) For most practical purposes, epoxy has no characteristic temperatures. Clarify! It is a rigid network polymer when formed, so has no T g . It decomposes rather than melts, on heating, so has no T m .

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2 3. A Kevlar fiber reinforced polyester composite having V fiber = 0.46 and E composite = 60 GPa is loaded in tension with 10 MPa of stress in the fiber alignment direction. Calculate the fraction of the load carried by the fibers. Note:
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## This note was uploaded on 01/10/2012 for the course ENSC 3313 taught by Professor Staff during the Fall '11 term at Oklahoma State.

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Exam3spring2004 - ENSC 3313 Spring 2004 TEST 3 KEY Name Answer all 10 questions show all work 2points each 1 How many kg of S are needed to cross

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