Response Surface Methodology for the Optimization and Characterization of Cassava Starch‐graft‐Poly(acrylamide)

Response surface methodology (RSM) was employed for the synthesis of cassava starch‐graft‐poly(acrylamide) using ceric ammonium nitrate as free radical initiator. Concentration of acrylamide, concentration of ceric ammonium nitrate, reaction temperature and duration of reaction were optimized using a 4‐factor 3‐level Box‐Behnken design. The dependent variables were percentage grafting (%G) and grafting efficiency (GE). Second order polynomial relationships were obtained for %G and GE, which explained the main, quadratic and interaction effects of factors. The highest%G and GE obtained were 174.8% and 90.7%, respectively. The optimum values of parameters predicted through RSM were 20 g acrylamide/10 g dry starch, 3.3 g/L ceric ammonium nitrate, 180 min reaction duration and 45ºC temperature with a %G of 190.0. For GE, the predicted levels of factors for the optimum value of 90.8% were 17.5 g acrylamide/10 g dry starch, 4.1 g/L ceric ammonium nitrate, 180 min reaction duration and 55ºC temperature. The graft reaction was confirmed by FTIR analysis, where the absorption bands corresponding to the C=O stretching and N‐H bending of the –CONH₂ group were observed. Scanning electron microscopic studies on grafted starches revealed that the granular structure of the starch was affected by the reaction. X‐ray diffraction analysis showed that the crystallinity of starch was decreased as a result of grafting and the reduction was higher for the grafted starches with higher percentage grafting.     

Study on Preparation and Thickening Efficiency of an Inverse Emulsion of Anionic Starch‐graft‐Polyacrylamide

A series of graft copolymers of starch with polyacrylamide was made by using a K₂S₂O₈ initiation system in inverse emulsion. The corresponding anionic graft copolymers, which have a different hydrolysis degree, are prepared by alkaline hydrolysis of the uncharged graft copolymers. Adequate hydrolytic conditions including type and amount of hydrolyzing agent, temperature, and time were studied. These graft copolymers have been tested for their temperature sensitivity, salt tolerance and shear stability, and a comparison has been made with ungrafted polyacrylamide (PAM). Experiments showed that a high hydrolysis degree can be obtained in a shorter time when NaOH and Na₂CO₃ were used together as hydrolyzing agents, and the highest solution viscosity was observed when the hydrolysis degree of the graft copolymers was approximately 30%, . In addition, the shear stability, temperature sensitivity and salt tolerance in the graft copolymers were also investigated.     

Microwave‐accelerated Synthesis and Characterization of Potato Starch‐g‐poly(acrylamide)

Using a very low concentration of potassium persulfate as initiator, acrylamide could be efficiently grafted onto potato starch under microwave irradiation and for the grafting O₂ removal from the reaction vessel was not required. Under optimal conditions, grafting and efficiency observed were 160% and 89%, respectively. Grafted starch was characterized by using Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) and thermogravimetric analysis (TGA). It was observed that the microwave irradiation could significantly accelerate the synthesis of starch‐graft‐poly(acrylamide), because under identical conditions no grafting was observed in a conventional procedure. Viscosity, shear stability and water/saline solution retention of the microwave‐synthesized grafted starch were studied and compared with that of the parent starch.     

Isocyanate‐free Route to Starch‐graft‐Polycaprolactone via Carbonyldiimidazole (CDI)‐mediated End Group Conversion

This paper reports on the synthesis of biodegradable starch‐graft‐poly ϵ‐caprolactone (starch‐g‐PCL) in two steps. First, poly ϵ‐caprolactone (PCL) was modified on the terminal groups by using carbodiimidazole (CDI) as coupling agent. Then, the starch graft copolymers with PCL were prepared through a carbonate bond using carboimidazole function. Monofunctional and bifunctional reactive end‐group PCL terminated with carboimidazole groups were prepared and reacted with hydroxyl groups of starch. The resulting starch‐g‐PCL copolymers were characterized by FT‐IR, NMR, HR‐MAS‐NMR, DSC, MEB and XRD.     

Synthesis,characterization and swelling behaviour of superabsorbent polymers from cassava starch‐graft‐poly(acrylamide)

Superabsorbent polymers (SAPs) were prepared from cassava starch by graft copolymerization of acrylamide on to starch using ceric ammonium nitrate (CAN) as free radical initiator, followed by alkali saponification. The reaction parameters such as concentration of acrylamide, concentration of CAN, temperature, and duration of polymerization reaction were optimized for maximum water absorbency using a 4‐factor 3‐level Box‐Behnken design. The highest values of percentage grafting and absorbency obtained were 174.8% and 425.2 g/g, respectively. The polymers were characterized by determination of grafting efficiency, N‐content, acrylamide content, FTIR analysis, SEM and XRD analyses. Thermogravimetric analysis (TG) showed that the SAP has higher thermal stability. The rate of water absorbency and the swelling behaviour of the SAP under different conditions of pH, and different salts were determined. The de‐swelling pattern of the hydrogels over different time durations was also determined.     

Water sorption kinetics of superabsorbent hydrogels of saponified cassava starch‐graft‐poly(acrylamide)

Superabsorbent polymers (SAPs) are hydrophilic polymeric networks that can absorb, swell and retain large quantity of water and other physiological fluids. In this paper, the water sorption pattern and kinetics of cassava starch based SAP hydrogels were studied under different conditions of swelling such as soaking duration, pH, presence of salts, and particle size of the hydrogel. The kinetics was studied using Voigt‐based viscoelastic model to determine the rate parameter and the swelling rate (SR). It was noted that under all conditions, the water sorption followed a second order kinetics. The absorbency was directly proportional to the rate of swelling. But when the sample was allowed to swell in aqueous solutions of CaCl₂ and AlCl₃, the absorbency as well as the SR was irregular. The particle size also had significant effect on water absorption by the SAP and the polymer with smaller particles showed more absorption than those with larger particle size. The solvent induced phase transition of the superabsorbent hydrogel was also studied.     

Preparation,characterization, and water resistance of cationic acetylated starch‐g‐poly(styrene‐butyl acrylate) surfactant‐free emulsion

Cationic acetylated starch‐g‐poly(styrene‐butyl acrylate) surfactant‐free emulsion (CAS‐g‐poly(St‐BA)) was synthesized by graft copolymerization of styrene (St) and butyl acrylate (BA) onto CAS using FeSO₄–H₂O₂ redox initiator. The maximum graft of 55.68% was derived when H₂O₂ concentration, monomer concentration, and St/BA ratio were 9%, 130%, and 1:1, respectively. The results obtained from FTIR, NMR (H¹ NMR and C¹³ NMR), XRD, SEM, and thermogravimetric analysis (TGA‐DTG) confirmed graft copolymerization of St and BA onto CAS. And it was demonstrated that film‐forming properties of starch were greatly improved via grafting St and BA onto starch. It was also found that paper sized with CAS‐g‐poly(St‐BA) exhibited higher ring crush index and bursting strength than paper sized with cationic potato starch (CS) and CAS, as well as much lower water absorption, which is further verified by contact angles results.     

Grafting of 2‐(Dimethylamino)ethyl Methacrylate onto Potato Starch Using Potassium Permanganate/Sulfuric Acid Initiation System

Graft copolymerization of 2‐(dimethylamino)ethyl methacrylate onto potato starch was carried out in an aqueous medium using a potassium permanganate/sulfuric acid initiation system. The grafting percentage and grafting efficiency were determined as functions of the concentrations of potassium permanganate, sulfuric acid and the monomer, and also polymerization temperature and time. The IR spectrum of the graft copolymer showed the peaks characteristic of the grafted chains. The grafting percentage and grafting efficiency increased and then decreased with increasing the concentrations of potassium permanganate, sulfuric acid, and the monomer, as well as polymerization temperature. The grafting reaction was characterized by an initial fast rate followed a lower rate which leveled off after a certain time. The overall activation energy for the grafting was estimated to be 66.9 kJ/mol.     

Effects of starch alkenylsuccinylation on the grafting efficiency,paste viscosity,and film properties of alkenylsuccinylated starch‐g‐poly(acrylic acid)

Commercial cornstarch was alkenylsuccinylated with alkenylsuccinic anhydride to different degrees of substitution (DS) and then the products were graft‐copolymerized with acrylic acid for investigating the effects of starch alkenylsuccinylation on the graft copolymerization with vinyl monomer, as well as on paste viscosity and film properties of alkenylsuccinylated starch‐g‐poly(acrylic acid) (ASS‐g‐PAA). The number of carbon atom of alkenyl in alkenylsuccinates considered was 8 and 12, corresponding to octenylsuccinylation and dodecenylsuccinylation of starch, respectively. The graft copolymerization was accessed by grafting efficiency, grafting ratio, and conversion of monomer to polymer, and the film properties of ASS‐g‐PAA considered included tensile strength, breaking elongation, and work‐to‐break. Experimental results demonstrated that the alkenylsuccinylation showed marked effects on the copolymerization, paste viscosity, and film properties. It resulted in increased grafting efficiency, stable paste viscosity, and strong starch film. Carbon‐chain length of the alkenyl and DS value of the alkenylsuccinates also exhibited evident effects on the copolymerization and film properties. Octenylsuccinylation of starch before the copolymerization was superior to dodecenylsuccinylation in improving the efficiency and film properties. Low levels of octenylsuccinylation could be utilized to increase the efficiency of the copolymerization and improve the properties of starch film.     

Effects of starch acryloylation on the grafting efficiency,adhesion, and film properties of acryloylated starch‐g‐poly(acrylic acid) for warp sizing

In order to enhance the grafting efficiency of graft copolymerization of granular cornstarch with acrylic acid (AA) for improving the adhesion and film properties of starch‐g‐poly(acrylic acid) used as sizing agent, the esterification of hydrolyzed starch with acryloyl chloride was applied before graft copolymerization. The influence of three common initiators on the copolymerization were also studied. The initiators included ceric ammonium nitrate [Ce(NH₄)₂(NO₃)₆], hydrogen peroxide/ferrous ammonium sulfate [H₂O₂/FeSO₄ · (NH₄)₂SO₄], and potassium persulfate/sodium bisulfite [K₂S₂O₈/NaHSO₃]. It was found that acryloylation of starch before the copolymerization was an effective method for substantially enhancing the grafting efficiency and improving the performances such as adhesion‐to‐fibers and mechanical properties of grafted starch film. The acryloylation could increase the efficiency to 67–81% when the degree of substitution (DS) of acryloylated starch ranged from 0.010 to 0.036. The adhesion to polyester and cotton fibers reached their maximum at DS = 0.010 and 0.022, respectively. Strong and tough film was obtained when the DS value was in a range of 0.010–0.022. H₂O₂/FeSO₄ · (NH₄)₂SO₄ redox system was more appropriate for initiating the copolymerization of acryloylated starch with AA.     

Fast‐swelling Superabsorbent Hydrogels from Poly(2‐hydroxy ethyl acrylate‐co‐sodium acrylate) Grafted on Starch

Fast‐swelling highly porous superabsorbent hydrogels were synthesized through a rapid radical polymerization under normal atmospheric conditions. To synthesize a biopolymer‐based superabsorbent hydrogel, 2‐hydroxyethyl acrylate (HEA) and sodium acrylate (AANa) were grafted on the starch backbone in an aqueous solution. The graft copolymerization reaction was carried out in the presence of ammonium persulfate (APS) as an initiator and ‐methylenebisacrylamide (MBA) as a crosslinker in a homogeneous medium. The chemical structure of the hydrogels was confirmed by FT‐IR spectroscopy and thermogravimetric analysis (TGA). The morphology of the samples was examined by scanning electron microscopy (SEM). The results indicated that with increasing the amount of sodium acrylate both swelling capacity and swelling under load (AUL) were increased. Preliminary swelling and deswelling behaviors of the hydrogels were also studied. The effects of pH and inorganic salt on the swelling behavior of the hydrogels were investigated as well.     

Reversible Regulation of Gelatinization of Potato Starch with Poly(ε‐lysine) and Amino Acids

Poly(ε‐lysine) (PL), lysine (Lys), monosodium glutamate (GluNa), glycine (Gly), alanine (Ala), and leucine (Leu) were used to regulate the characteristic gelatinization behavior of potato starch. As determined by differential scanning calorimetry, PL, Lys, and GluNa with positive or negative net charge elevated the gelatinization temperature with increasing amount added as compared with the small effect of Gly, Ala, and Leu with zero net charge. The peak viscosity evaluated by a Rapid Viscoanalyser was markedly decreased by adding PL, Lys, and GluNa, whereas Gly and Ala had no effect on the peak viscosity. The swelling was also decreased by added PL, Lys, and GluNa, whereas it was unchanged by added Gly, Ala, and Leu. Potato starch immersed in PL or amino acid solution released most of the retained PL and amino acids by the subsequent washing with water. The increased gelatinization temperature of the PL‐treat­ed potato starch returned to the original value by washing with water. It is thus considered that the regulatory effects of PL and amino acids on the gelatinization behavior of potato starch were substantially reversible.     

Influence of Citric Acid on the Properties of Glycerol‐plasticized dry Starch (DTPS) and DTPS/Poly(lactic acid) Blends

In the presence of citric acid (CA), one‐step extrusion processing is used to prepare poly(lactic acid)/thermoplastic dry starch (PLA/DTPS) blends (50/50, %, w/w) in a single‐screw extruder. The rheological study proves that CA decreases the viscosity of both DTPS and of DTPS/PLA blends. The low viscosity increases the dispersion and decreases the interfacial tension between DTPS and PLA, as shown by scanning electron microscopy (SEM). In the presence of CA, the tensile strength of DTPS/PLA reaches 41 MPa—similar to that of pure PLA—because of improved dispersion and compatibility. At the same time, CA increases not only the degradation of starch, but also the interaction between DTPS and PLA, as detected by Fourier transform infrared (FTIR) spectroscopy. The blend containing CA has a higher thermal stability. The water absorption of DTPS and DTPS/PLA blends is also studied.     

Compatibilisation of starch/poly(butylene adipate co‐terephthalate) blends in blown films

Reactive extrusion was utilised for starch/poly(butylene adipate co‐terephthalate) (PBAT) blown film production, using maleic anhydride (MA) and citric acid (CA), alone or combined, as compatibilisers. These compounds (2% w/w) were added to the starch/PBAT (55:45) mixture after dispersion on glycerol. More rigid films, with greater tensile strength (9.82 ± 0.45 MPa), were produced when 2.0% CA was used. The opposite, little homogeneity and poor tensile strength (0.77 ± 0.12 MPa) and elongation (2.67 ± 0.67%) were found in films produced using 2.0% MA. Barrier properties to water vapour were improved by compatibilisers. FTIR analysis showed that CA and MA were able to promote esterification/transesterification reactions. Blends containing CA also showed better phase compatibilisation in the scanning electron microscopic images. It was found that in mixtures containing MA, the process and the concentration of this reagent need to be adapted to produce films with improved properties.     

Antimicrobial Efficacy of Poly (DL‐lactide‐co‐glycolide) (PLGA) Nanoparticles with Entrapped Cinnamon Bark Extract against Listeria monocytogenes and Salmonella typhimurium

Nanoencapsulation of active compounds using poly‐(d,l ‐lactide‐co‐glycolide) (PLGA) is commonly used in the pharmaceutical industry for drug delivery and may have important applications in the food industry. Control of growth of foodborne bacteria with the goals of reducing the number of foodborne illness outbreaks, assuring consumers a safer food supply remains a priority in the food industry. Natural antimicrobials are an excellent way to eliminate pathogens without introducing chemical preservatives that consumers may find undesirable. Cinnamon bark extract (CBE) is an effective pathogen inhibitor isolated from cinnamon spice. PLGA nanoparticles containing CBE were produced using an emulsion‐solvent evaporation method and characterized for size, polydispersity, morphology, entrapment efficiency, in vitro release and pathogen inhibition. PLGA with 2 different ratios of lactide to glycolide (65:35 and 50:50) were used to determine how polymer composition affected nanoparticle characteristics and antimicrobial potency. The size of the nanoparticles ranged from 144.77 to 166.65 nm and the entrapment efficiencies of CBE in 65:35 PLGA and 50:50 PLGA were 38.90% and 47.60%, respectively. The in vitro release profile at 35 °C showed an initial burst effect for both types of PLGA followed by a more gradual release of CBE from the polymer matrix. Both types of PLGA nanoparticles loaded with CBE were effective inhibitors of Salmonella enterica serovar Typhimurium and Listeria monocytogenes after 24 and 72 h at concentrations ranging from 224.42 to 549.23 μg/mL. The PLGA encapsulation improved delivery of hydrophobic antimicrobial to the pathogens in aqueous media.     

A Review of Poly(Lactic Acid)‐Based Materials for Antimicrobial Packaging

Poly(lactic acid) (PLA) can be synthesized from renewable bio‐derived monomers and, as such, it is an alternative to conventional petroleum‐based polymers. Since PLA is a relatively new polymer, much effort has been directed toward its development in order to make it an acceptable and effective option to the more traditional petroleum‐based polymers. Commercially, PLA has received considerable attention in food packaging applications with a focus on films and coatings that are suitable for short shelf life and ready‐to‐eat food products. The potential for PLA to be used in active packaging has also been recognized by a number of researchers. This review focuses on the use of PLA in antimicrobial systems for food packaging applications and explores the engineering characteristics and antimicrobial activity of PLA films incorporated and/or coated with antimicrobial agents.