Novel antimicrobial organic thermal stabilizer and co-stabilizer for rigid PVC

Article abstract of DOI:10.3390/molecules17077927

Biologically active N-benzoyl-4-(N-maleimido)-phenylhydrazide (BMPH) was synthesized and its structure was confirmed by elemental analysis and various spectral tools. It was examined as a thermal stabilizer and co-stabilizer for rigid poly (vinyl chloride) at 180°C in air. Blending BMPH with reference samples in different ratios greatly lengthens the thermal stability value and improves the extent of discoloration of PVC. TGA confirmed the improved stability of PVC in presence of the investigated organic stabilizer. GPC measurements were done to investigate the changes occurred in the molecular masses of the degraded samples of blank PVC and PVC in presence of the novel stabilizer. BMPH showed good antimicrobial activity towards two kinds of bacteria and two kinds of fungi.

Full text of DOI:10.3390/molecules17077927

Molecules 2012, 17, 7927-7940; doi:10.3390/molecules17077927
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Novel Antimicrobial Organic Thermal Stabilizer and
Co-Stabilizer for Rigid PVC
Mona M. Fahmy, Riham R. Mohamed and Nadia A. Mohamed *
Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt
* Author to whom correspondence should be addressed; E-Mail: namadm@hotmail.com.
Received: 18 May 2012; in revised form: 15 June 2012 / Accepted: 18 June 2012 /
Published: 2 July 2012
Abstract: Biologically active N-benzoyl-4-(N-maleimido)-phenylhydrazide (BMPH) was
synthesized and its structure was confirmed by elemental analysis and various spectral
tools. It was examined as a thermal stabilizer and co-stabilizer for rigid poly (vinyl
chloride) at 180 °C in air. Blending BMPH with reference samples in different ratios
greatly lengthens the thermal stability value and improves the extent of discoloration of
PVC. TGA confirmed the improved stability of PVC in presence of the investigated
organic stabilizer. GPC measurements were done to investigate the changes occurred in the
molecular masses of the degraded samples of blank PVC and PVC in presence of the novel
stabilizer. BMPH showed good antimicrobial activity towards two kinds of bacteria and
two kinds of fungi.
Keywords: PVC; thermal stability; discoloration; antimicrobial activity
1. Introduction
It is generally known that poly (vinyl chloride), PVC, is an unstable polymer when exposed to
high temperatures during its molding and applications. PVC undergoes extensive autocatalytic
dehydrochlorination with formation of conjugated double bonds [1]. This in turn leads to unacceptable
discoloration of the polymer and changes in its physical and mechanical properties [2–4], together with
a decrease or an increase in its average molecular weight as a result of chain scission or crosslinking. It
has been generally considered that thermal dehydrochlorination is initiated by structural defects such
as allylic chlorine associated with internal unsaturation [5], tertiary hydrogen and chlorine atoms

Molecules 2012, 17
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associated with branches [6], reactive terminal groups such as double bonds [5], oxygen-containing
groups [7], or peroxide residues [8] and head-to-head structures [9].
Thus, stabilization of PVC against thermal degradation is essential for its processing and use at high
temperatures. The thermal stabilizers commonly in use for the stabilization of PVC are either basic
lead salts [10], which can react with the evolved HCl gas, thus retarding its deleterious catalytic action,
metallic soaps [11] and esters or mercaptides of dialkyltin [12] that can exchange the labile chlorine in
the backbone chains for other more stable ester or mercaptide groups derived from the stabilizer.
In spite of the fact that the aforementioned classes of stabilizers are quite efficient industrially, the
metallic residues of some of these organometallic compounds (lead, cadmium or tin) may present
serious environmental problems. Others, such as zinc, form chloride salts which are strong catalysts
for the subsequent dehydrochlorination process, and are responsible for the sudden blackening of
certain formulations. For this reason, the attention of many investigators has been directed recently to
stabilizers of a fully organic nature [13–27]. Moreover, studies were performed to prepare antibacterial
PVC. These trials were based on surface modification of PVC using different nanoparticles to prepare
PVC/antibacterial composites. Zirconium phosphate [28] and TiO2/Ag [29] were used for this purpose.
Isothiocyanate nucleophilically substituted PVC was also used to obtain an antibacterial PVC [30]. On
the other hand, pyrazolodithiones with antimicrobial and antitumor activity have been used recently as
additives for thermal stabilization of rigid PVC [26].
N-substituted maleimides [31] and aromatic hydrazides [32] have been proven to be effective
additives for PVC stabilization against thermal degradation. However, the aromatic hydrazides act as
HCl absorbers; the maliemides act as powerful radical traps and can exchange the labile chlorine in the
PVC chains for a more stable maleimide moiety.
Thus, it became of interest to study the thermal stability of PVC in the presence of a novel organic
stabilizer, N-benzoyl-4-(N-maleimido)-phenylhydrazide (BMPH), which combines the characteristics
of both the maleimide and hydrazide groups in its structure. BMPH was prepared for the first time in
this work and its structure was confirmed by elemental analysis and several spectral tools. It was also
characterized for its antimicrobial activity.
2. Results and Discussion
2.1. Preparation and Characterization of N-benzoyl-4-(N-maleimido)-phenylhydrazide (BMPH)
BMPH was synthesized from maleic anhydride, p-aminobenzoic acid and benzhydrazide, as shown
in Scheme 1.
BMPH: Yield: 75.8%; m.p. = 164–166 °C. Elemental analyses: Theor. C (64.47%), H (3.91%),
N (12.53%) and O (19.09%); Exp. C (64.04%), H (3.86%), N (12.13%) and O (18.98%).

Molecules 2012, 17
7929
Scheme 1. The synthesis of BMPH.
O
O
C
HC
HC
HC
HN
COOH
H2N
COOH
+
O
O
DMF
C
HC
p-Aminobenzoic acid
COOH
room temp /5 h
Maleic anhydride
N-(4-Carboxyphenyl) maleamic acid
Ac2O/AcONa
O
55-60oC / 2h
O
SOCl2
reflux, 2 h
N
COCl
N
COOH
O
O
N-(4-Chlorocarbonylphenyl) maleimide
N-(4-Carboxyphenyl) maleimide
O
C
+
CH2Cl2/ Triethylamine
NHNH2
Benzhydrazide
O
N
CONH-NHCO
N-Benzoyl-4-(N-maleimido)phenyl hydrazide
BMPH
O
FTIR spectrum of BMPH (Figure 1) showed a specific band for maleimide moiety at 830 cm−1,
while two strong bands appeared at 1509 and 1603 cm−1 corresponding to the stretching vibration for
aromatic rings. Moreover, a strong band for the stretching vibration of carbonyl groups of hydrazide
linkage appeared at 1650 cm−1. A specific band appeared at 1714 cm−1 for the C=O of the imide
linkages of the maleimide moiety. Also the -NH- stretching band appeared at 3239 cm−1.
Figure 1. FTIR spectrum of BMPH.

Molecules 2012, 17
7930
1H-NMR spectrum of BMPH (Figure 2) (DMSO): δHe = 7.0 ppm. (2H, -NH-); δHd = 7.5–7.6 ppm
(5H, aromatic protons); δHc = 7.9 ppm (2H, o-H); δHb = 8.0 ppm (2H, m-H), δHa = 8.1 ppm (2H,
H-C=C-H). MS m/z: 335 (M+).
Figure 2. 1H-NMR spectrum of BMPH.
H
H
d
H
d
H
O
c
b
O
C
O
C
H
a
H
d
N
O
N
e
N
e
H
H
H
H
H
d
H
H
d
a
c
b
BMPH
2.2. Stabilization of Thermally Degraded Rigid PVC Using BMPH
Results of the dehydrochlorination of rigid PVC thermally degraded at 180 °C in air, in the presence
of the investigated stabilizer are shown both in Figure 3 and Table 1. The results of the non-stabilized
blank PVC as well as those of the samples stabilized by DBLC and Ca–Zn stearate used as reference
stabilizers are also given for comparison. The results reveal that BMPH exhibits a greater stabilizing
efficiency than those of the two reference stabilizers, which is shown by the longer thermal stability
value (Ts) during which no detectable amounts of hydrogen chloride gas are liberated (Table 1). The

Molecules 2012, 17
7931
thermal stability value of BMPH is almost three or four times higher than the values obtained for the
reference stabilizers.
Figure 3. Dehydrochlorination rate of rigid PVC (DBLC, Ca-Zn stearate, BMPH) at
180 °C, in air, in the presence of 2 mass % of BMPH stabilizer and reference stabilizers.
Table 1. Thermal stability values of rigid PVC thermally degraded at 180 °C in air, in the
presence of BMPH, reference stabilizers and mixed stabilizers.
Type of stabilizer
Blank PVC
Ts/min
0
DBLC
7
Ca-Zn stearate
6
BMPH
22
30
50
35
31
50
30
BMPH + Ca-Zn stearate (75%:25%)
BMPH + Ca-Zn stearate (50%:50%)
BMPH + Ca-Zn stearate (25%:75%)
BMPH + DBLC (75%:25%)
BMPH + DBLC (50%:50%)
BMPH + DBLC (25%:75%)
It has been previously suggested that maleimide derivatives owe their stabilizing efficiency to the
replacement of the labile chlorine atoms on PVC chains by a relatively more thermally stable stabilizer
moiety. The stabilizers’ efficiency is attributed to their radical potency, which interferes with the PVC
radical degradation process. This most probably occurs not only through trapping the radical species in
the degradation process, but also by blocking the radical sites created on PVC chains. The radical
attack seems to occur first on the ethylenic carbon–carbon double bond, followed by cleavage of
the imide linkages during the later stages of degradation. This mode of action has previously been
published, together with the experiments to prove it [31]. Furthermore, aromatic hydrazides are
efficient thermal stabilizers for rigid PVC. They exhibit their stabilizing efficiency through effective
absorption of the degradation products (HCl gas) by their basic groups [32].

Molecules 2012, 17
7932
In view of structural similarity of BMPH to maleimides combined with aromatic hydrazides, the
mechanism of BMPH is outlined by assuming that its first part (maleimide) can work as a radical
trapper, while its other part (benzhydrazide) acts as HCl absorber.
Other experimental evidence for the high stabilizing efficiency of BMPH is illustrated by the
improvement in the extent of discoloration of PVC samples stabilized with BMPH and thermally
degraded at 180 °C in air for different time intervals relative to blank PVC sample and PVC samples
stabilized with any of the reference stabilizers (Table 2). This reflects the greater stabilizing efficiency
of BMPH through the replacement of the labile chlorine by a more thermally stable stabilizer moiety
which disturbs the formation of the conjugated double bonds that are responsible for discoloration.
Table 2. Extent of discoloration of thermally degraded rigid PVC at 180 °C in air for
various time intervals, in presence of different stabilizers.
Type of
stabilizer
Blank PVC
DBLC
Ca-Zn stearate
BMPH
Color at
0 min
White
White
White
White
Color at
15 min
Light brown
Light brown
Orange
Color at
25 min
Dark brown
Brown
Light brown
yellow
Color at
35 min
Black
Dark brown
Dark brown
Dark yellow
Color at
45 min
Black
Dark brown
Dark brown
Light brown
yellow
Moreover, the improvement in the extent of discoloration of PVC in presence of BMPH is most
probably due to its dienophilic properties, which allow it to intervene with the conjugated double bond
systems formed by Diels-Alder addition on PVC chains during the subsequent stages of the degradation
process. Several investigators have attributed the good color stability of the dibutyltin maleate
stabilizer to the same type of addition reaction [33].
2.3. Elucidation of the Molecular Mass by GPC
GPC measurements were carried out for both PVC, before and after 30 min of thermal degradation
in presence or absence of BMPH stabilizer. Results are summarized in Table 3, where the values of
Mw, Mn and polydisperity (PD) are shown.
Table 3. GPC measurements of degraded PVC samples.
Sample
Degradation
Time/min
Mw
(g/mol) × 104
24.473
Mn
(g/mol) × 104
9.1520
PD
PVC Blank
PVC
PVC + BMPH
0
30
30
2.674
4.3535
3.3845
18.702
20.570
4.2958
6.0777
The GPC measurement results indicate the low decrease in the values of molecular masses of PVC
samples achieved by using BMPH as thermal stabilizer. The results of GPC measurements show the
decrease in Mw value of blank PVC sample from 2.4473 × 105 to 1.8702 × 105 upon 30 min of thermal
degradation with a % decrease in Mw value of 23.58. After the same time of degradation, the decrease
in Mw of a PVC sample stabilized with BMPH reaches only 15.94%.

Molecules 2012, 17
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This may be due to the good stabilizing effect of the investigated compound that decreases the
extent of chain scission of PVC. The solubility test of thermally degraded PVC indicates the absence
of gel formation, which indicates the absence of cross linking during degradation. This is evidence for
the high efficiency for the investigated stabilizer, that it can decrease the chain scission and prevent
cross linking, so it can preserve both the mechanical and physical properties of the polymer.
2.4. Thermogravimetric Analysis
Thermal stability and degradation behavior for blank PVC and PVC stabilized with BMPH were
investigated by TG measurements. The results obtained are given in Table 4. BMPH greatly improved
the initial decomposition temperature of PVC, as the IDT of PVC stabilized with BMPH was recorded
as 265 °C, whereas the IDT of the non-stabilized PVC was found to be 180 °C. Furthermore, at all
temperatures used, PVC samples stabilized with BMPH showed higher stability (lower mass loss %)
relative to that of blank PVC. These results suggest that the degradation rate of PVC sample stabilized
with BMPH is slower than that of blank PVC sample. From the aforementioned results, it was clear
that BMPH stabilizer had increased the thermal stability of PVC.
Table 4. Thermogravimetric data of blank PVC and PVC in presence of BMPH stabilizer.
T (°C)
Blank PVC
PVC + BMPH
Initial Decomposition
Temperature (IDT)
180 °C
265 °C
T (°C)
200
Mass loss (%)
5
0
250
280
300
350
11
32
44
61
65
0
23
40
53
60
400
2.5. Effect of Mixed Stabilizers on the Stabilization Efficiency of Thermally Degraded Rigid PVC
It was of interest to study the effect on the efficiency of stabilization of mixing BMPH stabilizer
with reference stabilizers. Mixing was done in the ranges of 0–100% of BMPH relative to DBLC or
Ca-Zn stearate reference stabilizers. The overall mixed stabilizers concentration was kept always
constant at 2 mass % of PVC and the results represent the average of three comparable experiments for
each stabilizer mixture. The results of the dehydrochlorination of thermally degraded rigid PVC at
180 °C, in air, in the presence of each combination are illustrated in Figures 4 and 5. The thermal
stability values of such combinations are listed in Table 1. The results reveal the existence of a
true synergistic effect resulting from the combination of BMPH stabilizer with any of the two
reference stabilizers.
The maximum synergism was achieved when the BMPH stabilizer was mixed with DBLC or
Ca–Zn stearate in an equivalent weight ratio. The results also demonstrated a slight improvement
in the rate of dehydrochlorination as a result of mixing the investigated stabilizer with the
reference stabilizers.

Molecules 2012, 17
Figure 4. Dehydrochlorination rate of rigid PVC (BMPH stabilizer was mixed with Ca-Zn
7934
stearate), at 180 °C, in air, in the presence of 2 mass % of mixed stabilizers.
Figure 5. Dehydrochlorination rate of rigid PVC (BMPH stabilizer was mixed with DBLC),
at 180 °C, in air, in the presence of 2 mass % of mixed stabilizers.
It has been established that the hydrazide linkage can interact with various transition metal salts to
form stable complexes [27]. For this, at subsequent stages of degradation, it would be possible for the
hydrazide moiety of BMPH stabilizer to react with the accumulated metal chlorides (ZnCl2 or PbCl2)
formed as by-products from reference stabilizers to form complexes with additional stabilizing power

Molecules 2012, 17
7935
and improve the stabilizing efficiency of the mixed stabilizers. Thus, mixing the reference stabilizers
with BMPH, would not only remove the deleterious effect of the metal chlorides but also it give an
additional advantage from their transformation into useful new stabilizers.
An additional proof for the synergistic effect achieved by mixing the investigated stabilizer with the
reference stabilizers on the extent of discoloration of rigid PVC thermally degraded at 180 °C, in air,
for 60 min (Table 5). The results clearly reveal that all the mixed stabilizers exhibit a reduction of the
discoloration of the PVC than the reference stabilizers, rather than the BMPH, when they are used
separately. The least extent of discoloration was achieved when the BMPH and reference stabilizers
were mixed in equivalent weight ratio.
Table 5. Extent of discoloration of rigid PVC thermally degraded at 180 °C in air, for
60 min, in the presence of different weight ratios of stabilizers.
Mixed
BMPH + DBLC
0%:100%
BMPH + DBLC
25%:75%
BMPH + DBLC
50%:50%
BMPH + DBLC BMPH + DBLC
stabilizer
75%:25%
100%:0%
Color
Mixed
Very dark brown
BMPH + Ca-Zn
stearate
Brown
BMPH + Ca-Zn
stearate
Yellow
BMPH + Ca-Zn
stearate
Dark yellow
Dark yellow
BMPH + Ca-Zn BMPH + Ca-Zn
stabilizer
stearate
75%:25%
Dark yellow
stearate
100%:0%
Dark yellow
0%:100%
25%:75%
Brown
50%:50%
Yellow
Color
Dark brown
2.6. Biological Activity for BMPH against Bacterial and Fungal Strains Isolated from Animal Origin
BMPH showed antibacterial activity of 52% of that of the reference antibacterial agent
(ciprofloxacin) against S. pneumonia, about 40% of ciprofloxacin against S. aureus, 60% of ciprofloxacin
against S. typhimurium and 58.8% of ciprofloxacin against E. coli bacteria (Table 6). Also, it has
antifungal activity as shown in Table 6. This activity represents 27% and 46.7% of the reference
antifungal agent (flucanazole) against two kinds of fungi; A. flavus and C. albicans, respectively.
Table 6. Antimicrobial activity of BMPH against some bacteria and fungi.
S. pneumonia
G (+ve)
S. aureus S. typhimurium
E. coli
G (-ve)
C. albicans A. flavus
G (+ve)
G (-ve)
BMPH
26
50
16
40
24
40
20
34
21
45
15
55
Ciprofloxacin (100 µg/mL)
(Antibacterial agent)
Flucanazole (100 µg/mL)
(Antifungal agent)
Thus, BMPH stabilizer exhibited reasonable biological activity due to the presence of either -NH
or -C=O groups in its structure and it is clear that its antibacterial activity is higher than its
antifungal activity.

Molecules 2012, 17
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3. Experimental
3.1. General
The commercial PVC (suspension) used in this study was additive free, with a K value of 70 and
supplied by Hüls Co. (Frankfurt, Germany). Calcium–zinc stearate complex (Ca-Zn stearate) obtained
from G. Siegle Co. (Stuttgart, Germany), and dibasic lead carbonate (DBLC) (Rolite lead) obtained
from the National Lead Co. (Darmstadt, Germany), were also used. The FTIR spectrum was recorded
1
on a Shimadzu FT-IR 8201 PC Spectrophotometer using KBr pellets. The H-NMR spectrum was
recorded with a Jeol 270 MHz (Tokyo, Japan) spectrometer in DMSO-d6 as a solvent and the chemical
shifts were recorded in ppm relative to TMS as an internal standard. Mass spectra were recorded
on GCMS-QP 1000 ex spectra mass spectrometer (Shimadzu, Tokyo, Japan) operating at 70 eV.
Elemental analyses were carried out by the micro-analytical unit at the National Research Centre,
Giza, Egypt.
3.2. Methods
3.2.1. Preparation of N-Benzoyl-4-(N-maleimido)phenyl hydrazide (BMPH)
BMPH was synthesized from maleic anhydride, p-aminobenzoic acid and benzhydrazide, as shown
in Scheme 1. Maleic anhydride (1 mol) and p-aminobenzoic acid (1 mol) were dissolved in DMF
320 mL), then the mixture was stirred at room temperature for 5 h under nitrogen atmosphere.
The resulting solution was then poured into a large amount of water to precipitate crude
N-(4-carboxyphenyl)maleamic acid, which was filtered, dried and recrystallized from water.
Yield = 97%; m.p. 223–225 °C (lit. [34] m.p. 225–226 °C).
A mixture of N-(4-carboxyphenyl)maleamic acid (0.2 mol), acetic anhydride (100 mL) and fused
sodium acetate (2.5 g) was stirred at 55–60 °C for 2 h. The reaction mixture was poured onto a large
amount of water to give crude N-(4-carboxyphenyl)maleimide, which was filtered and washed with
water, dried and recrystallized from methanol: water (6:1) mixture. Yield = 85%; m.p. 211–212 °C
(lit. [35] m.p. 208–210 °C).
A mixture of N-(4-carboxyphenyl)maleimide (0.16 mol), thionyl chloride (4.02 mol) and
tert-butylcatechol (0.01 g) was refluxed for 2 h. Unreacted thionyl chloride was evaporated out,
and then the residual product was recrystallized from benzene to obtain pure N-[4-(chloro-
carbonyl)phenyl]maleimide. Yield = 73.3%; m.p. 166–167 °C (lit. [34] m.p. 168–169 °C).
A solution of ethyl benzoate (0.2 mol) in absolute ethanol (200 mL) was treated with an excess of
hydrazine hydrate (20 mL). The reaction mixture was heated under reflux with constant stirring for
3 h, and the resulting solution was cooled in the refrigerator for 24 h. Benzhydrazide was separated as
solid particles, filtered and dried under vacuum. It was recrystallized from ethanol. Yield = 94%; m.p.
116–117 °C (lit. [27] m.p. 115–117 °C).
A solution of 5.44 g (0.04 mol) benzhydrazide dissolved in 100 mL DMF was stirred well, and
allowed to cool at −10 °C using ice-salt bath for 15 min. Then 9.42 g (0.04 mol) solid N-(4-chloro-
carbonylphenyl)maleimide was added slowly with constant stirring for 1 h. Ice-salt bath was removed
to let the temperature of condensation reaction rise gradually to room temperature and maintained for

Molecules 2012, 17
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additional 2 h with stirring. The reaction mixture was slowly poured onto methanol-water mixture
(1:2), upon which a white precipitate of BMPH is immediately formed. The product was filtered, dried
and recrystallized from 1:1 methanol-water mixture.
3.2.2. Preparation of Stabilized PVC Samples
Samples of PVC for thermal degradation were prepared by thoroughly mixing 1 g of PVC powder
with 2 mass % of the stabilizer (or mixed stabilizers) in a mortar and 0.2 g of the resulting fine powder
was used in the investigation.
3.2.3. Method of Evaluation of the Stabilizing Efficiency
Evaluation of the stabilizing efficiency was carried out by measuring the rate of dehydrochlorination
using a continuous potentiometric determination of the evolved hydrogen chloride gas at 180 °C in air.
A detailed description of this method was given elsewhere [36]. The extent of discoloration of the
degraded PVC samples was evaluated visually as a function of degradation time. The results obtained
are the average of three comparable experiments in each case.
3.2.4. Thermogravimetric Analysis
Thermogravimetric analysis (TG) measurements were made with a Shimadzu TG-50 H thermal
analyzer system. Samples were heated from 0 to 500 °C in a platinum pan at a heating rate of
10 °C min−1 in a nitrogen atmosphere (30 mL min−1).
3.2.5. Molecular Mass Determination by GPC
Average molecular mass of PVC was determined using GPC - HPLC, Waters 600 System
controller, 717 plus autosampler. Columns: Phenomenex Phenogel 5 μm 50 A, 300 × 7.8 mm;
Detection: Waters model 2410 refractive index; ATTN = 16 × Eluent: THF (100% by Vol.); Flow rate:
0.7 mL min−1; Temperature: 50 °C; Injection volume: 25 μL. Standards: Polystyrene (PS) 25,000;
−1
13,000; 4000; 2500; 200 g mol−1 (1.0% m v ). Cubic fit calibration curve by Waters Millennium
32 GPC System Software. Samples: Dissolved in THF at an approximate 1.0% m v−1 concentration.
3.2.6. Antimicrobial Activity of BMPH
Antimicrobial activity of the investigated sample was determined using a modified Kibry-Baur disc
diffusion method [37–40] at Cairo University-Microanalytical Center. The disk diffusion method for
filamentous fungi was performed using the approved standard method (M38-A) developed by
researchers [41] for evaluating the susceptibilities of filamentous fungi to antifungal agents. The disc
diffusion method for yeasts was performed using the standard method (M44-P) approved by the
NCCLS [42]. Agar-based methods such as E-test and disk diffusion can be good alternatives because
they are simpler and faster than broth-based methods [43,44].

Molecules 2012, 17
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4. Conclusions
BMPH is an efficient stabilizer for the thermal degradation of rigid PVC relative to other common
industrial reference stabilizers such as DBLC and Ca-Zn stearate. Its greater stabilizing efficiency is
based on its longer thermal stability value and its better extent of discoloration and its lower extent of
chain scission together with no gel formation which lead to preservation of both the mechanical and
physical properties of the polymer. TGA studies indicated that BMPH improved the thermal stability
of PVC as judged by the increase in its IDT and by the decrease in its mass losses (%) at a particular
temperature. Mixing BMPH with two reference stabilizers in different proportions greatly improves
the thermal stability values and also the extent of discoloration. The maximum synergism was obtained
in the equivalent weight ratio of BMPH and any of the reference stabilizers. Thus, it is possible to
recommend the use of BMPH as a thermal stabilizer for rigid PVC, either alone or as a co-stabilizer
with various industrial organometallic stabilizers. Moreover, BMPH stabilizer exhibited reasonable
biological activity and it is clear that its antibacterial activity is higher than its antifungal activity.
Thus, it can be used as a useful additive for PVC in biomedical and clinical fields.
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