Magdy W. Sabaa

DEGRADATION AND STABILIZATION OF POLY(VINYL CHLORIDE)

Abstract Poly(viny1 chloride) (PVC) has many desirable characteristics that have allowed it to achieve its present status as one of the most important commercial polymers. In spite of its enormous technical and economic importance, PVC still possesses many problems. Its rather low stability to the influence of heat and light results in discoloration, hydrogen chloride loss, and serious corrosion phenomena [1], accompanied by changes in the mechanical properties of the article together with a decrease or an increase in molecular weight as a result of chain sassion or crosslinking of the polymer molecules, respectively [2].

Organic thermal stabilizers for rigid poly(vinyl chloride) I. Barbituric and thiobarbituric acids

Abstract Barbituric acid (BA) and thiobarbituric acid (TBA) have been investigated as thermal stabilizers for rigid poly(vinyl chloride) (PVC) at 180°C, in air. The efficiency of these compounds as thermal stabilizers was evaluated by measuring the length of the induction period ( T s ), during which no detectable amount of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric titration on one hand, and the extent of discoloration of the degraded polymer on the other. The stabilizing efficiencies were compared with that of dibasic lead carbonate (DBLC), dibasic lead stearate (DBLS), barium–cadmium–zinc stearate (Ba–Cd–Zn stearate), n -octyl tin mercaptide ( n -OTM) and dibutyl tin maleate (DBTM). With the exception of DBTM reference stabilizer which shows a comparable stabilizing efficiency with BA and TBA, the investigated organic stabilizers exhibit a greater efficiency than those of all other reference stabilizers. Moreover, they impart better color stability to the degraded samples. A radical mechanism for the stabilizing action is suggested. The stabilizing efficiency is attributed to the replacement of the labile chlorine atoms on the PVC chains by a relatively more stable moiety of the stabilizer. This disrupts the formation of conjugated double bonds, which are responsible for the discoloration.

Polysaccharide based graft copolymers

From the contents: Polymer Grafting: A Versatile Means to Modify the Polysaccharides.- Cellulose graft copolymers: Synthesis, Properties and Applications.- Starch-g-copolymers: Synthesis, Properties and Applications.- Chitosan-g-copolymers: Synthesis, Properties and Applications.- Gum-g-copolymers: Synthesis, Properties and Applications.- Dextran-g-copolymers: Synthesis, Properties and Applications.- Polysaccharide hydrogels: synthesis, characterization and applications.- Hyaluronic acid-g-copolymers: Synthesis, Properties and Applications.- Polysaccharide based graft copolymers for biomedical applications.

Quaternized N-substituted carboxymethyl chitosan derivatives as antimicrobial agents

Introduction of quaternary ammonium moieties into N-substituted carboxymethyl chitosan (N-substituted CMCh) derivatives enhances their biological activity. Several derivatives of CMCh having a variety of N-aryl substituents bearing either electron-donating or electron withdrawing groups have been synthesized by the reaction between amino group of CMCh with various aromatic aldehydes under acidic conditions, followed by reduction of the produced Schiff base derivatives with sodium cyanoborohydride. Each of the reduced derivatives was further quaternized using N-(3-chloro-2-hydroxy-propyl)trimethylammonium chloride (Quat-188). The resulting quaternized materials were characterized by FTIR and (1)H NMR spectroscopy. Their antibacterial activities against Streptococcus pneumoniae (S. pneumonia, RCMB 010010), Bacillis subtilis (B. subtilis, RCMB 010067), as Gram positive bacteria and against Escherichia coli (E. coli, RCMB 010052) as Gram negative bacteria and their antifungal activities against Aspergillus fumigatus (A. fumigates, RCMB 02568), Geotricum candidum (G. candidum, RCMB 05097), and Candida albicans (C. albicans, RCMB 05031) were examined using agar disk diffusion method. The results indicated that all the quaternized derivatives showed better antimicrobial activities than that of CMCh. These derivatives are highly potent against Gram positive bacteria compared to Gram negative bacteria. This is illustrated for example as the values of minimum inhibitory concentration (MIC) of Q4NO2-BzCMCh against B. subtilis and S. pneumonia were 6.25 and 12.5 μg/mL, respectively corresponded to 20.0 μg/mL against E. coli. The antimicrobial activity of quaternized N-aryl CMCh derivatives affected by not only the nature of the microorganisms but also by the nature, position and number of the substituent groups on the phenyl ring. Thus while the derivatives with groups of electron withdrawing nature show higher inhibition zone diameter and lower MIC values relative to that of those having electron-donating nature, the non-substituted derivative lies between these two extremes. Antibacterial activities of Q4NO2-BzCMCh, Q3Cl-BzCMCh and Q3Br-BzCMCh against E. coli are nearly equivalent to that of the standard drug Gentamycin. Q3Br-BzCMCh emerged almost equivalent antibacterial activity to Ampicillin against S. pneumonia.

Gamma radiation induced graft copolymerization of vinylimidazole-acrylic acid onto polypropylene films

Comonomers of vinylimidazole (VI) and acrylic acid (AA) have been grafted onto Polypropylene (PP) films using γ-radiation. The effect of the comonomer composition on the percent graft was investigated. The reactivity ratio of the prepared copolymers was determined by conventional methods. IR spectroscopy, surface morphology, mechanical properties, dyeability, as well as thermal stability of the grafted samples were also studied.

Synthesis and characterization of antimicrobial crosslinked carboxymethyl chitosan nanoparticles loaded with silver.

Carboxymethyl chitosan (CMCh)-silver nanoparticle (Ag) hydrogels with high antibacterial activity against three Gram +ve bacteria (Staphylococcus aureus, Bacillus subtilis and Streptococcus faecalis), three Gram -ve bacteria (Escherichia coli, Pseudomonas aeruginosa and Neisseria gonorrhoeae) and a Candida albicans fungus were prepared. The in situ preparation reaction involved crosslinking of CMCh with epichlorohydrin in alkaline medium containing silver nitrate to yield silver nanoparticles loaded CMCh hydrogel giving pale brown or darker hydrogels when the silver content increases. FTIR spectroscopy, SEM and TEM were done for the prepared hydrogels. Silver nanoparticles hydrogels exhibited higher antimicrobial activity than virgin CMCh. TEM analysis showed the small size of the prepared hydrogels to be in the range of 9-16nm in size.

Organic thermal stabilizers for rigid poly(vinyl chloride) II. Benzal thiobarbituric acid and some of its derivatives

Abstract Benzal thiobarbituric acid (BTBA) and two of its derivatives: para -methoxy benzal thiobarbituric acid ( p -MeO-BTBA) and para -chloro benzal thiobarbituric acid ( p -Cl-BTBA) have been investigated as thermal stabilizers for rigid PVC at 180°C, in air. Their stabilizing efficiency is based on measuring the rate of dehydrochlorination and the extent of discoloration of the degraded polymer. The results reveal the higher stabilizing efficiency of the investigated materials as thermal stabilizers for rigid PVC as compared with the industrially used thermal stabilizers: dibasic lead carbonate (DBLC), dibasic lead stearate (DBLS), n -octyl tin mercaptide ( n -OTM), dibulyl tin maleate (DBTM) and barium–cadmium–zinc stearate (Ba–Cd–Zn stearate). This is well illustrated by the longer induction period ( T s ) values and by the lower rate of dehydrochlorination. The stabilization efficiency is affected by the nature of the substituent found in the phenyl ring of the BTBA derivatives. Moreover, it was found that these materials lower the extent of discoloration of the polymer during degradation as compared with the reference stabilizers. A radical mechanism for the stabilizing effect of BTBA and its derivatives is proposed. The effect of blending p -Cl-BTBA with either of the reference stabilizers on the stabilizing efficiency of the thermally degraded rigid PVC has been also investigated. The results reveal that mixing of the stabilizers improves both the T s values, the rate of dehydrochloration and the extent of discoloration. This improvement attains its maximum when both the investigated and the reference stabilizers are taken in equivalent weight ratio.

1-Cyanoethanoyl-4-acryloyl thiosemicarbazide and its metal complexes as thermal stabilizers for rigid poly(vinyl chloride)

Abstract 1-Cyanoethanoyl-4-acryloyl thiosemicarbazide (CEATS) and its metal complexes with Sn 2+ , Cd 2+ , Co 2+ ions have been investigated as thermal stabilizers for rigid poly(vinyl chloride). The results reveal that the stabilizing efficiency of CEATS is comparable to that of the commonly used industrial stabilizers, while the stabilizing efficiencies of CEATS complexes greatly exceed that of the parent molecule. CEATS as a co-stabilizer with reference stabilizers namely Cd–Ba stearates, dibutyl tin maleate, or basic lead sulfate led to a synergistic effect. A probable mechanism expressing the interaction of CEATS molecule with metal salts stabilizers has been proposed.

Cyanoguanidine and its complexes as thermal stabilizers for rigid poly(vinyl chloride)

Abstract Cyanoguanidine and its complexes with cadmium and zinc have been investigated as thermal stabilizers for rigid PVC, at 180°C, in air. The results reveal the higher stabilizing efficiency of the investigated materials as shown by the longer induction periods obtained in their presence relative to those using dibutyl tin maleate, cadmium-barium stearate and basic lead carbonate, which are commonly used industrial stabilizers. The stabilizing efficiencies of the complex derivatives are higher than those of the parent cyanoguanidine. A synergistic effect is observed when cyanoguanidine is blended in various molar ratios with either of the soap stabilizers. The synergistic effect is probably due to the ability of cyanoguanidine for in-situ complexation with the metal chlorides which result as stabilization by-products, thus protecting the polymer from their deleterious accelerating degradative effect. An ionic mechanism for the stabilizing effect of cyanoguanidine and its derivatives is proposed.

N-substituted maleimides as thermal stabilizers for plasticized poly(vinyl chloride)

Abstract N -Substituted maleimides have been investigated as thermal stabilizers for plasticized PVC at 180°C in air by measuring the rate of dehydrochlorination and the extent of discoloration of the degraded polymer. The results reveal a higher stabilizing efficiency of the products investigated compared with basic lead carbonate, dibutyl tin maleate, and barium-cadmium stearate stabilizers which are commonly used industrially. The induction period (Ts) is influenced by the nature and position of substituents in the aryl ring together with the nature of the plasticizer used. Moreover, it has been found that the stabilizers investigated impart better color stability to the degraded samples compared with the stearate stabilizer. A synergistic effect was achieved when the products investigated were used as mixtures with the reference stabilizer in equimolar ratios. A radical mechanism is proposed which illustrates the stabilizing action of the products investigated.