8. Results and discussion

Transcription

1 8. Results and discussin 8. 1 The bttm edge ignitin test The untreated unsized plyester fabric burned ut cmpletely within 30 secnds. The vertical burn test results are presented in Appendix The results shw that excellent self-extinctin times can hwever be achieved at relatively lw add-n levels with the xygenated hydrcarbn flame retardants. Fr example, dipentaerythritl requires an add-n f just abve tw percent t be effective as a flame retardant with a selfextinguishing time f apprximately three secnds. Similar results were btained when the fabric was treated with benzphenne and slid epxy resin Epikte 1001 (ligmers f the diglycidyl ether f bisphenl A) frm Shell Chemicals. The average self-extinguishing time fr the latter was abut ne secnd, and fr the frmer abut three secnds. Interestingly, the add-n vs. self-extinctin time curve fr pentaerythritl starts t rise again abve an add-n f abut 20 percent, as shwn in Figure 8. These results imply that sme f the xygenated hydrcarbn flame retardants may be effective in an intermediate cncentratin range nly. Such behaviur was previusly als bserved with hindered N-alkxy amines (NOR-Hals) as flame retardants in plyprpylene fabrics (Srinivasan et ai, 1998). 62

2 80 70 f ~~ -.. e Pentaerythritl 60 r- -~', ~ -~ ~ 50 I/) ';' 40 E ~ 30 en 20 \ --- Dipentaerythritl _ Mass %Add-n Figure 8: Self-extinguishing times versus add-n f Pentaerythritl and dipentaerythritl treated plyester fabric. The same behaviur was als bserved with phsphrus flame retardants and with phsphrus mineral filler synergism (Weil, 1992). Using vertical burn tests (NFPA 701), plyprpylene fibre and films passed the test with the additin f 1 % NOR-Hals, but when the cncentratin was raised t 10% the test was failed., - Figure 9 shws the self-extinguishing time and the mass p~rcentage addn fr plyester fabric treated with Phlrglucinl and Insitl. The line represents the average values f the samples. The Phlrglucinl had an average self-extinguishing time f 1 secnd and the Insitl an average self-extinguishing time f 4 secnds. 63

3 c.i CI) III... CI) E ;; w C/) ~ """"- " --" ". "" " - " " ""." " --. ".. " ~. --Phlrglucinl - " " " " Insitl Mass % Add-n Figure 9: Self extinguishing times versus add-n f Phlrglucinl and Insitl treated plyester fabric. Figure 10 shws the self-extinguishing time and the mass percentage addn fr plyester fabric treated with 2-Furic acid, Epikte 1001 and Benzphenne. 12 ~ ~ (.) CI)... III CI) E 6 :;; w C/) Furic acid ~ -~ ~ Epikte' Benzphenne 2 ~~~~~~~~~~~~--~~~ Mass % Add-n Figure 10: Self extinguishing times versus add-n f 2-Furic acid, Epikte 1001 and Benzphenne treated plyester fabric. 64

4 Frm Figure 10 it is evident that sme f the xygenated hydrcarbn flame retardants exhibit the same behaviur, in that there is a parablic relatinship between the self extinguishing time and the mass percentage add-n. Benzphenne has an ptimum mass percentage add-n at abut 2 %, with a self-extinguishing time f 2 secnds. 2-Furic acid and the Bisphenl A based resin Epikte 1001 bth display almst the same self extinguishing time f less than ne secnd at an mass percentage add-n level f 7.5 %. Figure 11 shws the results btained with Benzyl phenyl ketne, Maltl and Benzic acid. These xygenated hydrcarbn cmpunds exhibit similar parablic behaviur as Figure 12 shw fr Benzyl benzate and Diethylphthalate. 25, , --Benzyl phenyl ketne -- rvblti Benzic acid "J Q).!!!. Q),g w 10 - en II Mass %Add-n Figure 11: Self extinguishing times versus add-n f Benzyl phenyl ketne, Maltl and Benzic acid treated plyester fabric. 65

5 25,..., U (I)... en (I) E :;:: w CJ) - Benzyl benzate DEP Mass % Add-n Figure 12: Self extinguishing times versus add-n f Benzyl benzate and Diethylphthalate treated plyester fabric. 8.2 The Puddle flame retardancy test The purpse f this test was t determine whether the fabric ignited and burned in a situatin where melt dripping was prevented Unfrtunately nne f the treated samples tested, ignited. Hwever, the untreated fabric burned fr apprximately 3 secnds. Puddle test results are cmpiled in Table 12. These reprted values represent average values measured fr,. the samples tested. Table 12 : Results btained frm the Puddle Test Additive Add-n [%] Percentage Mass lss Pure PES Pentaerythritl Dipentaerythritl Phlrglucinl Isphthalic acid

6 Surprisingly, as shwn in Table 12, the pure plyester fabric shwed a lwer mass lss than the treated fabrics. The highest mass lss was bserved with Dipentaerythritl as additive. During the vertical burn test the dipentaerythritl treated samples displayed fast melt dripping. These results suggest that the additive enhances the plymer slid t gas cnversin. B.3 The Face ignitin flammability test Table 13 shws the results btained with the Face Ignitin test n untreated fabric. The average values fr the treated fabrics are shwn in Table 14. Figure 13 t 17 shw the fabric samples after the Face Ignitin test. Table 13 : Results f the Face Ignitin Test fr Pure Plyester fabric. Sample Percentage mass Lss* Area f Hle (mm 2 ) A B C 1.4 Cnsumed cmpletely D * Crrespnds t the dripped mass cllected belw the sample. Mass cnsumed by cmbustin was assumed negligible. It is bserved during this test that the stretched fabric first cntracts at the pint where the flame impinges befre melting starts. Then a hle starts t frm that is surrunded by a ridge f mlten plymer. The hle expands wing t an apparent utward pulling frce. This frce might arise frm 67

7 build in stress caused by the riented plymer chains in the fibres. An alternative explanatin invlves the surface tensin frces in the mlten plymer bead. Table 14: Average results frm the Face Ignitin Tests. Additive Percentage Percentage Hle Mass mass lss Area [mm 2 ] add-n Pure PES >5800 Pentaeryth ritl Dipentaerythritl Phlrglucinl Isphthalic acid Figure 13: Untreated Plyester fabric samples after the Face Ignitin test was applied. Figure 13 shws sme results after untreated samples have undergne the Face Ignitin test. The black residue is char residue and/r st frm the cmbustin prcess. It depsited n the clder surfaces f the fabric during the burning prcess. It is evident that the shape f the burn hle is 68

8 neither unifrm nr symmetric in shape. The damage t the fabric is inclined twards ne side f the munted sample. Mlten plymer drps. can be clearly seen n the sides f the hle, as well as a dwnward flw f plymer melt. The area f the hle in the untreated plyester fabric is als variable ranging frm the smallest t the largest f all the samples tested. Sample A samp!~ s';-,.. ::--~ "}..) ~~ ~!,-I.". 13:'.~;,.iP: j Figure 14: Plyester samples treated with Pentaerythritl. 69

9 In the case f the treated samples, there is less evidence f charring and the hles burned int the fabric have a mre runded shape. In additin, mst f the samples did nt ignite at all. The Pentaerythritl treated plyester samples frm Figure 14 shws n black carbn residue whatsever. Thus there was n discernable cmbustin f mlten plymer during the test. In this case the hle in the fabric frmed quickly and the mlten plymer flwed away rapidly. On the fabric samples treated with Dipentaerythritl shwn in Figure 15 there is almst n evidence f burning f the mlten plymer melt. The Dipentaerythritl samples melted and burned slightly slwer than the Pentaerythritl treated samples. Dripping f the mlten plymer ccurred at a fast rate. I... & ",':.J - ;. i>... "..;, ' -r:-' ~- - ~. S~,mple D \ -V " r.,,'...., :.?' Figure 15: Plyester samples treated with Dipentaerythritl On the fabric samples treated with Phlrglucinl shwn in Figure 16 there is slight evidence f burning f the mlten plymer melt. The Phlrglucinl samples melted and burned slightly faster than the Pentaerythritl treated samples. Dripping f the mlten plymer ccurred at a very fast rate as can be seen by the streaks f drps n the slid fabric. 70

10 Sample E... ~, ~. 4./;. J ~( Sample F.. ~' 'A..... ~ I..;..:'t k. jj~ \..* ~ :. ~ 1 1 _.. 1. ~. Figure 16: Plyester samples treated with Phlrglucinl. On the fabric samples treated with Isphthalic acid shwn in Figure 17 there is n evidence f burning f the mlten plymer melt. The Isphthalic acid samples melted and burned slightly slwer than the Pentaerythritl treated samples. Dripping f the mlten plymer ccurred at a mderately fast rate. Sample G,~.' \., -' }$" '. Figure 17: Plyester samples treated with Isphthalic acid 71

11 8.4 Plymer dripping test Figure 18 depicts the results frm a typical drip test. The average values btained fr the plymer drip test are shwn in Table 15. Except fr isphthalic acid, the presence f additives led t an increased tendency t drip. Pentaerythritl treated samples dripped at the fastest rate, almst 70 % faster than the bserved rate fr the untreated sample. 2.5 II' I/) 0 2 I/) I/) ~ E... Q) C) >... :;; ~ :l E :l u Time [5] Figure 18: Typical drip test result fr Pentaerythritl. Table 15 : Results btained frm the plymer dripping.tests. Additive Crrelatin cefficient, R Rate f dripping [g/s] Untreated Pentaeryth ritl Dipentaerythritl Phlrglucinl Isphthalic acid

12 8.5 Differential Scanning Calrimetry and Differential Thermal Analysis The results btained fr Differential Scanning Calrimetry are shwn in Figure 19 fr the untreated and the treated plyester fabrics. It is clear that the additives affect the shape and psitin f the melting endtherm peak fr the flame retarded plymer. Interestingly, the additives shift the peak temperature t higher values. The bserved heat f melting was apprximately 52 kj/g fr all the samples s:.s : u::: _.- -- r <1> I --- x , Pentaerythritl - Dipentaerythritl Phlrglucinl - Isphthalic acid -PES TeC) 270 Figure 19: DSC curve f PES and treated PES samples. Endthermic up, scan-rate f 1 aoc/min in xygen atmsphere. 73

13 - The results fr the Differential Thermal Analysis (see Figure 20) cnfirm the results btained with DSC. The melting nset-temperatures bserved in the DTA were higher fr treated samples than fr the pure PES. The reasns fr these bservatins are nt currently understd ~! - -- _. --- ~-... F\Q] faaa;~~06;:i'h-a -5 -_ --~ - ~.t. fls -ci" - - ClOOO()OOC»CYY ~~ LL, I ~ Pentaerythritl - _ 000_ W -- ~ J: - Dipentaerythritl 0 0 "., t.- Isphthalic acid Phlrglucinl PES -30 '---'-----'------' '-----'------'------' L-----'-----' J-----'----'---' '------'-----' J-----'------'-----' L-----'----'--L-'-----,------, ,--.J Figure 20: DTA curve f PES and treated PES samples. Endthermic dwn, scan-rate f 10 C/min in nitrgen atmsphere., - 74

14 8.6 Thermgravimetric Analysis The results btained with Thermgravimetric Analysis are shwn in Figure 21. All samples shw similar rapid vlatilisatin, with a mass lss f ca. 80% between 400 C and 420 C. Further mass lss ccurs at a slwer rate up t abut 580 C and is cmplete fr the untreated plyester fabric. The additives appear t affect this secnd degradatin step. The presence f the additives als appear t reduce the rate f mass lss, and als results in higher levels f char residue. Fr example, the Isphthalic acid treated sample prvided the best perfrmance with respect t char frmatin, and Phlrglucinl treated samples degraded almst cmpletely. u; f/) f/) m E (1) C') m c: -60 (1) CJ... Q) c , --"'"'"-'" - Pentaerythritl - Dipentaerythritl - Isphthalic acid - Phlrglucinl -PES ' !!! I Figure 21: TGA results fr PES and treated PES samples. 75

15 8.7 Rhemetry The lss mdulus fr the treated and untreated fabrics is shwn in Figure PES -0- Penta lr- Dipenta -x- Phlr <> T ('e) Figure 22: Lss mdulus frm parallel plate rhemetry f PES and PES treated samples. G*(r) is the frequency dependant cmplex dynamic mdulus cnsisting f a real and cmplex part. G'(r) is the real part that is in phase with the strain and is called the strage mdulus. G"(r) is the cmplex part called the lss mdulus, defined as the rati f the cmpnent 90 ut f phase with the stress t the stress itself. G * (aj) = G'(aJ) + ig"(aj) 76

16 G'((O) therefre measures the amunt f energy stred and G"((O) the amunt f energy dissipated by the material. It is therefre pssible t say that in Figure 22 the sample treated with Pentaerythritl, which shws the highest lss mdulus, is altered in such a way that a lt f energy is dissipated and very little recvered. The untreated fabric sample exhibits the lwest lss mdulus. Figure 23 shws the strage mdulus f the strage mdulus f the treated and untreated fabric samples. It strengthens the results frm the lss mdulus, as can be expected PES Penta Dipenta -x- Phlr -c a (!) <> x -x -x -x -x -x -x-x-x 1 -x -x -x 'jjx ""x T ('C) Figure 23: Strage mdulus parallel plate rhemetry f PES and PES treated samples. 77

17 Unfrtunately, there was n clear insight int the mechanism f the xygenated hydrcarbn flame retardants, btained frm the viscsity analysis (see Figure 24). It culd hwever nw be said that the viscsity plays nt the nly rle in the mechanism, but is nly part f a bigger picture. There was n significant increase in viscsity ver the melt temperature range, s the additives did nt cntribute a temperature dependent viscsity alteratin. Cii' (1l ~.t: PES -0- Pentaerythritl -- Dipentaerythritl x - Phlrglucinl Isphthalic acid x "'----x -- -=--- x ~ "-Q(~ ~--==<J =ls- ~ = T[C] Figure 24: Viscsity respnse parallel plate rhemetry f PES and PES treated samples. Parallel-plate rhemetry prduced a surprising result. Accrding t the data f Figure 24, the additives tend t increase melt viscsity in the temperature range f 220 C t 240 C rather than inducing the expected reductin. Unfrtunately, it was nt pssible t measure the viscsity at higher temperatures mre relevant t the flame retardancy prcess e.g. in the regin f 400 C. 78