Publisher’s version / Version de l'éditeur:
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la
première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
Questions? Contact the NRC Publications Archive team at
PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
Materiaux et constructions. Materials and Structures, 10, 59, pp. 289-296,
1977-09
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.
https://nrc-publications.canada.ca/eng/copyright
NRC Publications Archive Record / Notice des Archives des publications du CNRC :
https://nrc-publications.canada.ca/eng/view/object/?id=c2b001e6-f01f-478e-909a-24648a787e69 https://publications-cnrc.canada.ca/fra/voir/objet/?id=c2b001e6-f01f-478e-909a-24648a787e69
NRC Publications Archive
Archives des publications du CNRC
This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
Outdoor durability of a common type (tetrachlorophtalic acid -based)
fire retardant glass fiber reiforced polyester (GRP) sheet
Ser
TH.1 1
N21d no.
757
2 - 2
National Research
Conseil national
I
#
Council Canada
de
recherches Canada
BLDG
OUTDOOR DURABILITY OF A COMMON TYPE
(TETRACHLOROPHTHALIC ACID-BASED) FIRE RETARDANT
GLASS FIBER REINFORCED POLYESTER (GRP) SHEET
by
A.
Blagaand
R
S. Yamasaki4
ANALYZED
Reprinted, fram
Mat6riaux et Constructions
VoL 10, No. 59, SeptemberIOctober 1977
p. 289 296
DBR Paper No.
757
Division of Building Research
Outdoor durability of a common type
(tetrachlorophthalic acid-based) fire retardant glass fiber
reinforced polyester (G R P) sheet
A. BLAGA ( I ) , R. S. YAMASAKI ( I )
Fire retardant GRP sheets based on tetrachlorophthalic acid-mod$ed polyester resin subjected to either artijicial or natural weathering undergo two types of surface dete- rioration (breakdown at the glass-resin interface resulting in jibre prominence and surface microcracking) 2.5 to 3 times faster than conventional sheets. Exposure to humidity- temperature cycles produces fibre prominence at comparable rates for both types of
GRP
sheets, but does not induce formation of surface microcracking.
The surface of the fire retardant sheets protected with weather-resistant poly (vinyl jluoride) (PVF) jilm does not undergo breakdown when subjected to accelerated or
natural exposures.
INTRODUCTION
In recent years, the matter of the fire hazard involved in the use of plastics in buildings has become of great concern to various regulatory authorities and specification agencies. The current trend is to demand greater resistance to flame and fire of glass-fibre rein- forced polyester (GRP) materials. Manufacturers have endeavoured to render these materials more fire- resistant by incorporating various fire-retardant addi- tives (e. g., antimony trioxide in conjunction with chlorinated organic compounds, phosphorus esters, and inorganic fillers) in the formulation or by using a matrix based on polyester resin with built-in fire resistance. Both of these approaches result in materials that have much lower outdoor weathering resist- ance ([I]-[4]). Usually, the GRP rendered fire resistant by incorporation of additives are the least weather- resistant; after a relatively short period of exposure, these materials lose most or all of their fire retard- ance [4] as a result of leaching of the additives. The sheets based on polyester resin with built-in fire retardancy retain their resistance during weathering, but show deterioration in other properties [2].
The reported information on the weathering perform- ance of fire retardant GRP is relatively limited. Most of the known weathering studies were performed on materials now out of date, representing technologies of 15 to 20 years ago. In view of this and given the emphasis on fire retardancy of plastic based materials,
( I ) Research Officers, Building Materials Section, Division of
Building Research, National Research Council of Canada, Ottawa, Canada.
a study was undertaken to investigate, by means of scanning electron microscopy, the relative durability of a popular commercial fire retardant GRP sheeting having built-in fire resistance and representing present- day technology. The matrix of the fire retardant GRP sheeting used is made of polyester resin based on tetrachlorophthalic acid (').
The purpose of this paper then is to discuss the nature and rate of breakdown of the aforementioned fire retardant GRP sheeting relative to general purpose (conventional) sheeting when subjected to accelerated and natural (outdoor) weathering. This paper also reports results on the effect of surfacing the fire retardant GRP sheeting with ~ol~(vinyT fluoride) (PVF) film on the weathering performance and on the influence of weathering on fire retardancy of these fire retardant GRP sheets (with and without PVF film).
EXPERIMENTAL Material
The GRP test samples (approximately 1.5 mm thick) were cut from commercial sheeting. A detailed description of the GRP sheets and their composition is presented in table I.
( 2 ) Subsequently this material will be referred to also as fire
VOL. 10
-
No 59-
MATERIAUX ET CONSTRUCTIONSTABLE I
DESCRIPTION OF G R P SHEETING (*) MATERIALS
Type Composition
Conventional. . . .
.
. . ..
. . . Sheets are composed of resin and glass (**)-reinforcement (25 weight %). The resin is based on cured thermosetting, UV light stabilized, general purpose polyester, produced by cross- linking 60 parts (***) of unsaturated polyester with 40 parts (***) of a 3 : 1 mixture of styrene and methyl methacrylate.Fire retardant (****).
. .
. . . Sheets composed of resin and glass (**)-reinforcement (25 weight %). Resin consisted of cured thermosetting, tetrachlorophthalic acid-based ultraviolet light stabilized unsaturated polyester (70 parts) (***) and cross-linked with styrene (30 parts) (***).Fire retardant, protected with ,
PVF surfacing film. . . ;. . .-r Composition is the same as for fire retardant type, but protected on both sides with an in-plant applied poly(viny1 fluoride) (PVF) surfacing film (0.025 mm thick) containing ultraviolet screening agents.
(*) Flat, smooth finish surface, non-gel coated, green and colorless translucent sheets. Made by a continuous automatic process.
(**) Silane-treated glass-fiber (E-glass) in the form of chopped strand mat. (***) By weight.
(****) Chlorine per cent (by weight) is such that a flat panel (1.5 mm thick) has an ASTME-84 tunnel test flame spread rating of 50.
Methods of weathering
To assess relative durability and eventual breakdown, test samples of conventional and fire retardant sheets (with and without PVF surfacing film) were subjected to accelerated aging and to natural weathering as described in table 11.
Assessment of surface damage
The progress of surface breakdown of the GRP sheets subjected to accelerated and natural weathering was followed with a Stereoscan scanning electron microscope (SEM). Generally, the SEM was operated at 20 kV. However, for examination of specimens protected with a poly(viny1 fluoride) (PVF) surfacing film, a voltage of 5 kV was used to prevent over- heating, which causes delamination of the surfacing film. A tilt angle of 45" was used for all specimens, which were coated first with carbon and then with gold to prevent surface charging.
Assessment of fire retardancy
The effect of outdoor weathering on the fire retard- ancy was assessed by the oxygen index test, in accordance with ASTM method D 2863.
RESULTS AND DISCUSSION
Selected SEM photomicrographs are presented in figures 1 to 15 to demonstrate the relative resistance to artificial and natural weathering and to illustrate the nature of surface breakdown of conventional and the fire retardant GRP sheets. The results and conclusions of this study are summarized in table 111.
Surface deterioration in the glass-resin interface. Fibre prominence
Owing to great dissimilarities in most properties (including thermal expansion, water absorption and strain response) of the main components, the glass- resin interface of the surface region is more susceptible to breakdown than the more homogeneous surface matrix. Thus surface breakdown in GRP sheets gene- rally occurs first in the glass-resin interface, as a result of environmentally-induced (usually thermally and/or by moisture) stress-fatigue ([5], [6]). The gradual breakdown of the matrix at the interface results in exposure of glass-fibres partly or almost completely delaminated (or debonded) but still retained at one or more points by the surface. This type of surface damage in a GRP sheet is referred to as "fibre prominence" or "fibre pop-out7'. The rate of break- down in the glass-resin interface resulting in fibre prominence depends on the GRP sheet material and the service environment.
These results show that generally tetrachlorophthalic acid polyester-based, fire retardant GRP sheets are considerably less resistant to surface breakdown at the glass-resin interface than conventional GRP sheets. When subjected to aging in the Weather-Ometer (table 111, method I), the fire retardant sheets deve- loped incipient fibre prominence after 250 to 300 cycles; the conventional sheets required 800 to 900 cycles to reach the same degree of deterioration. Figures 1 and 2 show the surface of the control (unweathered) samples of the conventional and fire retardant GRP sheets, respectively.
Figures 3 and 4 show two stages of fibre prominence in the fire retardant GRP sheets, after 400 and 1,200 cycles of Weather-Ometer exposure, respectively. Fibre prominence on the surface of conventional sheet is still not very extensive even after 1,200 cycles
Cfig. 5). Similarly, outdoor weathering (table 111,
method 2) induced initial features of fibre prominence in the fire retardant sheets after an exposure period of approximately one-third that required to produce the
A. BLAGA - R. S. YAMASAKI
TABLE I1
METHODS OF ENVIRONMENTAL AGING OF GRP SHEETS
Method No. 8 G e n e r a l D e s c n p f ~ o n of u e t a l l r *
Aging Candltlons
I C y c l l c v a r l a t l o n of h u m l d l f y ,
,
4h water s p r a y (100: RHtomporature and radiation (at1l.r and lZ°C)"", 4h radlatlon xenon Arc w e a t h e r - h e t e r ) (50% Rll and 5SDC) **; 3 c y c l e s
p e r d a y
2 Outdoor weathering a t otrawa s a m p l e s exposed h o r i z o n t a i l y , ( t e m p e r a t e n o r t h e r n c l l m a r e l v x t h no b a c k ~ n g , I" a c c o r d a n c e
w ~ f h ASnl 01435.
3 Cycllc v a r i a f l a n of h u m l d l t y 7h at 100% RH and 5bnC **, and 5h
and t e m p e r a t u r e (hmlnco a t 25 t o 100% RH and 1 1 to 56-C '*: C l l m a f e Lab). 2 c y c l e 5 p e r day.
" 4 d d l r l o n a i d e t a i l s are gllien ~n Reference 5 , figures 1 and 2
** T c m p f r a f u r c s were measured at t h e p a n e l s u r f a c e . Fig. 1. - Conventional GRP sheet. Control.
same damage at the glass-resin interface in conven-
tional sheets ( 5 to 6 versus 18 to 20 months). After
36 months of weathering this type of surface deterio-
ration is very extensive, as seen in figure 6, where
there are a large number of exposed fibres. The conven- tional sheets still had only a limited amount of fibre prominence on the exposed side even after 39 months
of outdoor weathering (jig. 7).
When exposed to humidity-temperature cycling (table 111, method 3), the conventional and the fire retardant sheets showed approximately the same rate and mode of surface breakdown in the glass-resin interface region. Figure 8 shows an example of a site of breakdown occurring at the glass-resin interface of the fire retardant GRP sheet after 400 cycles of exposure. Initially, however, the surface deterio- ration at the interface of the conventional GRP sheets proceeded at a rate about three times higher for sheets subiected to humidity-temperature cycling (me-
Fig. 2. - Fire retardant GRP sheet. Control. thod 3) thAn for those exposed i n the weather-~&eter
(table 111). This indicates that humidity-temperature
Fig. 3. - Fire retardant GRP sheet aged in the Weather-Ometer for 400 cycles.,
Lycling (by method 3) initially produces more severe stress-fatigue in the glass-resin interface of the surface layer than exposure in the Weather-Ometer. However, subsequent deterioration proceeded at much lower rates than in those sheets exposed in the Weather- Ometer and outdoors.
The unexposed (back side) of the sheets subjected to humidity, temperature and radiation cycling in the Weather-Ometer or to outdoor weathering, generally underwent surface deterioration in the glass-resin interface, qualitatively having damage features similar to those of the front (exposed) side. This is illustrated in figure 9; the breakdown on the back side of the least weather resistant material, the fire retardant GRP
sheet, weathered for 36 months, is limited to a few
sites on the surface. The degree of deterioration is comparable to that of the front side weathered outdoors for only 10 to 12 months.
Generally, the rate of over-all deterioration in the glass-resin interface of the back side is considerably lower (by a factor of 2 to 3) than that of the front
VOL. 10
-
No 59 - MATERIAUX ET CONSTRUCTIONSFig. 4. - Fire retardant G R P sheet aged in the Weather-Ometer Fig. 7. - Conventional G R P sheet weathered outdoors foz
for 1,200 cycles. 39 months.
Fig. 5. - Conventional G R P sheet aged in the Weather-Ometer Fig. 8. - Fire retardant G R P sheet subjected to humidity-
for 1,200 cycles. temperature cycling for 400 cycles.
Fig. 9. - Back side of fire retardant G R P sheet exposed outdoors
Fig. 6. -Fire retardant G R P sheet weather outdoors for 36 months. for 36 months.
A. BLAGA - R . S. YAMASAKI
Fig. 10. - Fire retardant G R P sheet aged in the Weather-Ometer Fig. 13. - Fire retardant G R P sheet weathered outdoors Tor
for 400 cycles. 36 months.
Fig. 11. - Fire retardant G R P sheet aged in the Weather-Ometer Fig. 14. - P V F coated, fire retardant G R P sheet aged in the
for 800 cycles. Weather-Ometer for 1,200 cycles.
Fig. 12. - Fire retardant G R P sheet aged in the Weather-Ometer Fig. 15. - P V F coated, fire retardant G R P sheet weathered
for 1,000 cycles. outdoors for 36 months.
VOL. 10 - No 59 - MATERIAUX ET CONSTRUCTIONS
side, confirming previous findings ([5], [7]). This can be explained as follows. Because the back side is not subjected to direct radiation (emitted by the Xenon Arc or by the sun) the exposure conditions there are much less severe. Thermal effects are thus considerably milder, e. g., lower surface temperature and reduced or no thermal shocks [5]. Furthermore, the surface resin of the back side of the sheet is not directly subjected to the harmful effects of ultraviolet light which promote cross-linking and other photolytic and photo-oxidative reactions in the resin. Thus the resin on the back side is less brittle than that on the front side, and consequently less susceptible to fracture ([5], [7]) under the influence of environmen- tally induced stress-fatigue.
Surface microcracking
Formation of microcracks in the surface matrix not in the immediate vicinity of the glass-resin inter- face was previously termed second stage deteriora- tion ([5], [6]). Generally, this type of breakdown occurs after the surface of the GRP sheet has deve- loped a significant amount of fibre prominence ([6],
[7]). The surface first develops single cracks having random orientations, then the cracks intersect to form a network. The formation of microcracks takes place under the combined influence of solar radiation and physically-induced stress-fatigue produced by the cyclic variation of humidity and temperature [6].
Results of this study show that exposure in the Weather-Ometer and outdoors causes the formation of surface microcracks at a much faster rate in the fire retardant than in conventional GRP sheets. The fire retardant GRP sheets developed incipient surface microcracks after 350 to 400 cycles in the Weather- Ometer (table 111, sample 2); the conventional sheets showed initial microcracks only after 1,225 to 1,250 cycles. Figures 3, 4, 10, 11 and 12 display the exposed surface of the fire retardant sheets at different magnifications and periods of exposure in the Weather- Ometer. After 1,200 cycles of exposure, fibre promi- nence is considerable and the surface microcracking very extensive (Jig. 4). The exposed surface of a con- ventional GRP sheet aged in the Weather-Ometer for 1,200 cycles is shown in figure 5; the matrix does not have any surface cracks.
Outdoor weathering produced incipient surface microcracks on the exposed side of the fire'retardant sheets after 34 to 36 months (table 111). The micro- tracks formed in the exposed surface of the fire retardant sheet weathered outdoors for 36 months are
shown in figure 13 ; the microcracks are fewer in number
and different from those that occur initially on the exposed surface of fire retardant GRP sheet aged in the Weather-Ometer (Jig. 3 and 10). This may be due to slower and more gradual shrinkage of the resin as a result of the lower rate of post-crosslinking in outdoor weathering than in Weather-Ometer aging. The con- ventional sheets did not show any signs of surface microcracks at the end (39 months) of the weathering program Cfig. 7).
Neither the conventional, nor the fire retardant GRP sheets developed surface microcracks on the back side (unexposed side) when subjected to accele-
rated (in the Weather-Ometer) or to outdoor weather- ing. This is illustrated in figure 9 for the material most susceptible to surface microcracking, the fire retardant GRP sheet. As shown, no surface micro- cracks are present after 36 months of outdoor weather- ing exposure. Similarly, GRP sheet samples exposed to humidity-temperature cycling in the absence of
radiation (table 111, samples 7 aria 8) did not show
any surface microcracking. This observation confirms the previously reported finding that to induce formation of surface microcracks, radiation is necessary [6].
Effect of PVF surfacing film on the weathering resistance
The tetrachlorophthalic acid based fire retardant GRP sheets protected with a surfacing poly(viny1 fluoride) film laminated during manufacture showed, good resistance to breakdown when exposed to accele- rated and natural weathering. With the exception of some incipient fibre ridgings after 36 months of outdoor weathering, the three types of exposure did not induce any other detectable surface damage in these sheets (table 111). Figures 14 and 15 show the surface of the fire retardant GRP sheet protected with PVF film after 1,200 cycles of exposure in the Weather-Ometer and 36 months of outdoor weathering, respectively. The surface texture of the exposed samples was found to be essentially similar to that of the controls. Thus the use of the PVF surfacing film protects the glass- resin interface against the harmful action of the envi-
r~nment, reducing the physically-induced stresses nor-
mally operating at the interface [5] by decreasing the amount of water sorbed; it also protects the surface matrix against the action of solar radiation because it contains ultraviolet screening agents.
Effect of weathering on fire retardancy
The unprotected fire retardant GRP sheets showed a slight improvement in fire retardancy at the end of 36 months of outdoor exposure, as evidenced by a statistically significant increase in the oxygen index (') (table IV). This may be attributed to the loss of residual monomer (styrene) during weathering. The fire retardant sheets protected with a surfacing PVF film showed no significant change, retaining their initial oxygen index. In this instance, the residual monomer in the GRP sheet was probably prevented from escaping by the surfacing film.
CONCLUSIONS
When subjected to artificial (in the Weather-Ometer) or natural weathering, fire retardant GRP sheets made from tetrachlorophthalic acid-based polyester resin
undergo much faster surface deterioration than GRP
sheets made from conventional polyester resin. Both types of surface deterioration, that at. the glass- resin interface resulting in fibre prominence and sur- face microcracking, proceed at rates 2.5 to 3 times faster than in conventional sheets. Exposure to humi-
( I ) The significance of the oxygen index is explained in the
A. BLAGA
-
R . S. YAMASAKI TABLE I11RELATIVE DURABILITY OF GRP SHEETS
Sxm- ' Ycthod Uescription of Type of Ibmnge to the Surface Total Conclu510n5
ple No. ' Sample [Time OF fir?t ~ccurtencr in cycles) Expo-
NO. Fibre Cracks Flbre Micro- sure
rldging along p r a m - cracking (cycles) fibres nence
1 I Conventional 3 - 4 15-18 800 - 1225 - 1250 Conventional sheet showed relatively
900 1250 good resistance to breakdown.
2 I Fire retardant <2 - 4 10 - 12 250 - 350 - 1250 Fire retardant sheets undergo faster
300 400 (approx. 3 tlmes) surface breakdown
I
(fibre prominence and mxcrocrack~ng)than conventional sheets.
I Fire retardant. None None None None 1250 The PVF surfacing film provides good protec-
protected with
I
tlon against breakdown by reducing the stressesPVF film induced by the environment* and by shield~ng
the surface from the action of UV radiation. i
4 23, Conventlonai c2 10-12 18 - j > 3 9
I
39 Conventional sheet showed relativelymos. mos. 20 mos. moi. mos. good resistance to breakdown.
5 2** tire retardant <2 c2 5 - 34-36 39 Fibre prornlnence develops at a rate
mos. mo5. 6nos. m o 5 . mos. more than 3 tlmes higher in fire retardant
I than in conventional sheets; fire retar-
dant sheets have also lower resistance to surface microcrack~ng.
6 2** Fire retardant. None None None None 39 The PVF surfacing film provides good
protected with mos . protection agalnst breakdown by reducing
PVF film the stresses induced by the environment'
and by shielding the surface from the action of W radiation.
7 3 Conventional c8 8-10 250 - None 1054 Relatively severe stress-fatigue*
350 operating at the glass-resin interface
produces mitially fibre prominence at a rate 3 times faster than ~n similar samples aged by method 1; surface microcracking does not occur m the absence of radiation.
8 3 Fire retardant <8 7 - 9 250 - None 1054 In the absence of radiation, formation of
300 fibre prominence proceeds at approximately
the same rate in fire retardant as in conventional sheets.
9 3 Fire retardant, None None None None 1054 The PVF surfacing film serves to protect
protected with the glass-resin interface of the surface
PVF film by reduclng the environmentally-induced
stresses* normally operating in the surface
regLon.
* As a result of cyclic vanation of humidlty andlor temperature, the surface region j s normally subjected to alternating stresses (induced by differential dimensional changes due to gradients and dissimilarity in properties between glass and resin). These exert a stress-fatigue on the surface material (5.6).
** Outdoor weather~ng time could not be converted into cycles, and is thus given in months (rnos.).
dity-temperature cycling produces similar surface break- down in the glass-resin interface region and at compa- rable rates in both types of GRP sheets, but does not induce formation of surface microcracks. Thus the matrix of the fire retardant sheet is more vulnerable
TABLE IV
EFFECT OF OUTDOOR WEATHERING ON FIRE RETARDANCY OF G R P SHEETS
Type of Oxygen Standard Comment.'*
Shret Index (n)' Dcviatlon
Fire
Retardant. j
a) Control , 28.7 0.2
b] Weathered*"' ! 30.5 0.2 Slight irnp~ovemcnt ~n fire
retardancy may be attributed to 105s of residual monomer.
Flre Retardant, Protected vlth PVF Fllm:
a) Control 28.5 0.1 . .
bl Weathered". 29.0 n.0 Fire retardancy 1 s essentially malntalned; the rc5ldual
monomer was probably prevented
from escaplng by the prorectlng fllrn.
, - -
than the matrix of the conventional sheet only when subjected to the combined action of radiation and physically-induced stresses (resulting from cycling of humidity and temperature).
The fire retardant GRP sheets protected with weather-
resistant PVF surfacing film showed remarkable per- formance when subjected to accelerated or natural exposures; the surface of the sheets did not show significant changes in surface properties. Since most of the deterioration occurs in the surface region, use of a highly weather-resistant conventional polyester
resin in the surface layer of the fire retardant GRP
sheet would also result in improved weathering per- formance. The same result could be achieved by using a weather-resistant coating which could be applied at the end of the curing cycle during the manufacture or after fabrication.
The authors wish to thank E. G. Quinn for coating
the specimens for SEM examination and R. L. Dubois
The oxygen index 1 s the mlnlmum concentration of oxygen (expre5scd a i for operating the Weather-Ometer.
volume in a mixture of oxygen and nlrrogen that wll: lust support flaming combustion of a material under the condltlons of the
tesr method (ASTM 02863); thus hlgher oxygen lndex lndlcates loirer This paper is a contribution from the Division of
flamr:ab~l~ry. Building Research of the National Research Council
** Dlmenslons of a l l specimens ,*ere 6.5 x 150 x 1.5 rnm. of Canada and is published with the approval of the
REFERENCES
[I] YUSTEIN, S. E. - U.S. Naval Appl. Sc. Lab., Lab.
Project 6035, Progress Rept. 4, 1963.
[2] RUGGER, G. R. - Weathering of glass reinforcedplastics.
Plastics Techn. Evaluation Centre, Picatinny Arsenal, Dover, N.J., 1966.
[3] WHITEHOUSE, A. A. K., WILDMAN, D. - 4th Int. Conf.
Reinf. Plast. BPF, Paper 28, 1964.
(41 PARKYN, B. - British Plastics, Vol. 32, No. 1, 1959,
p. 29.
DurabilitC a I'atmosph&re d'un type courant
(a
based'acide tetrachlorophthalique) de feuilles de polyester
renforcbes de fibres de verre (GRP) inhibitrices de
flamme. - La nature et la vitesse de ddtirioration des
placages inhibiteurs deflamme GRP ( a base de polyester modifid a l'acide tetrachlorophtalique) par rapport a celles des GRP ordinaires ont ktk ktudides par exposition d'kchantillons a des variations d'humiditk et de tempd- rature duns une machine de vieillissement artficiel a arc de xknon, ainsi qu'au vieillissement naturel. On a aussi ktudid I'efSet du surfacage de feuilles de GRP inhibitrices de jlamme par du jluorure de polyvinyl sur la durabilitk du GRP et sur la facon dont est modijide l'action du vieillissement naturel sur les propridtds inhibitrices de flamme. Les modijications superficielles de texture ont dtd examindes au microscope dlectronique a balayage. Qu'elle soit soumise au vieillissement artficiel ou au vieillissement naturel, la surface de la feuille de GRP inhibitrice de jlamme subit des ddtdriorations (pertes d'adhdrence entre la rdsine et les fibres qui se traduit par une nervuration des fibres en surface et par une
[5] BLAGA, A,, YAMASAKI, R. S. - Mechanism of break-
down in the interface region of glass reinforced polyester bp or-tificial weathering. J . Mat. Sc.. Vol. 8, 1973, p. 654.
[6] BLAGA, A., YAMASAKI, R. S. - Mechanism of surface
microcracking of matrix in glass reinforced polyester by artz$cial weathering, Vol. 8, 1973, p. 1331.
[7] BLAGA, A. - Weathering study of glass-j'iber reinforced
polyestnr sheets by scanning electron microscopy, Poly-
mer Eng. Sc., Vol. 12, 1972, p. 53.
microjissuration superjicielle) de 2,5 a 3 fois plus rapides que le GRP ordinaire. L'exposition au cycle humidite'ltempdrature produit une nervuration des fibres
ci des tenipkratuvcs comparables pour les deux types de
feuilles de GRP, mais elle ne dktermine pas de micro- jissuration superficielle.
La surface des feuilles inhibitrices dejlamme protkgdes par un jilm de fluorure de polyvinyl rdsistant aux intem- pdries ne subit pas de perte d'adhkrence fibrelrksine
quelque soit le mode d'exposition.
Les feuilles de GRP inhibitrices de jlamme non protkgkes montrent une ldgire amklioration de leurs propriitb inhibitrices de jlamme a p r b 36 mois d'expo- sition naturelle comme le met en e'vidence une augmen- tation statistiquement probante de l'indice d'oxygine. On peut l'attribuer a une perte du monomire rdsiduel (styrine) au cours de l'exposition. Les feuilles inhibi- trices de jlamme protkgkes par un jilm de jluorure de polyvinyl ne montrent pas de modfications notables, l'indice dJoxyg2ne initial restant constant; cela peut s'expliquer par le fait que, durant l'exposition, le phe'no- m2ne re'siduel a ktd emp2chk de se libkrer par le $film protecteur.
