Free-radical-initiated grafting of maleic anhydride (MA) onto a polylactide (PLA) backbone was performed by reactive extrusion. A concentration of 2 wt % MA in the presence of 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane (Lupersol 101) as the freeradical initiator was used for all experiments. Two reaction temperatures were studied (180 and 200°C) with a peroxide initiator concentration between 0.0 and 0.5 wt %. Under these conditions, between 0.066 and 0.672 wt % MA was grafted onto the PLA chains. Triple-detector size-exclusion chromatography (TriSEC), melt flow index (MFI), and thermal gravimetric analysis (TGA) were used to characterize the maleated PLA polymers. Increasing the initiator concentration resulted in an increase in the grafting of MA, as well as a decrease in the molecular weight of the polymer. The maleation of PLA proved to be very efficient in promoting strong interfacial adhesion with corn native starch in composites as obtained by melt blending.
Michigan Biotechnology InstituteLansing, Michigan 4891 0The reactive extrusion of polylactide (PLA) with a free radical initiator resulting in a branched polymer was accomplished. Reaction conditions were in the range of 160°C to 200°C with an initiator concentration between 0.0 and 0.5%. Triple detector size exclusion chromatography, melt flow index, thermal gravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis were used to characterize the polylactide polymers. PLA without initiator showed extensive degradation as was evidenced by a decrease in both molecular weight and melt viscosity The optimum range for branching resulting in a high molecular weight and low melt flow index polylactide was found to be around 170°C to 180°C and 0.1 to 0.25% initiator. MTIZODUCTIONtors. Free radical chemical reaction via reactive extruolylactide (PLA) is an important biodegradable and P biocompatible polymer that is now finding commercial use in single-use disposable items, in addition to the established applications in medical implants (l), sutures (2, 3). and drug delivery systems (4). The need for biodegradable polymers in the context of designing materials for the environment opens up new markets of opportunities for pol.ylactide polymers (5). However, one of the limitations ior using PLA is its processing instability (6). G0golew:jki (7) has shown that the degradation of PLA already occurs at 160°C under injection molding. Another shortcoming of PLA is its very low melt viscosity, which may limit its blow molding processability (8). The free radical branching of PLA could offer the opportunity for enhancement of physical and chemical properties and/or improvements of processability by increasing the molecular weight in order to compensate ,for the molecular weight decrease by processing degradation and by increasing the melt viscosity. The proposed free radical process is very simple and easy to manage by reactive extrusion in the presence of trace amounts of free radical initia-__._ _._ . __T o whom correspondence should 1 k addressed sion has been done extensively on polypropylene and polyethylene systems, leading to controlled degradation (9) and branching (lo), respectively. The reactive extrusion of PP with a free radical initiator, usually an organic peroxide, has been shown to lead to chain scission and hence molecular weight degradation (1 1).Pabedinskas et al. (12) have recently tried to model this system with the explicit purpose of developing a process control strategy. In contrast, the reactive extrusion of polyethylene, linear low density polyethylene (LLDPE) for instance, and a free radical initiator lead to a high molecular weight polymer as the initiator is increased (9. 13, 14). The purpose of this paper is to investigate the results of the free radical initiated branching of PLA extruded at temperatures ranging from 160°C to 200°C with an initiator concentration between 0.0% and 0.5%. The modified PLA samples were characterized by several analytical methods, including tr...
Enterococcus faecalis 710C, isolated from beef product, has a broad antimicrobial activity spectrum against foodborne pathogens. Two bacteriocins, enterocin 7A (Ent7A) and enterocin 7B (Ent7B), were purified from the culture supernatant of E. faecalis 710C and characterized using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry and electrospray infusion tandem mass spectrometry analyses. These data and subsequent genetic analysis showed that Ent7A and Ent7B are produced without N-terminal leader sequences and have amino acid sequences that are identical to those of enterocins MR10A and MR10B, respectively. However, the observed masses for Ent7A and Ent7B are 5200.80 and 5206.65 Da (monoisotopic mass), respectively, which are higher than the theoretical molecular masses of MR10A and MR10B, respectively. This study provides evidence that both Ent7A and Ent7B are formylated on the N-terminal methionine residue. Purified Ent7A and Ent7B are active against spoilage microorganisms and foodborne pathogens, including Clostridium sporogenes , Listeria monocytogenes , and Staphylococcus aureus as well as Brevundimonas diminuta , which has been associated with infections among immune-suppressed cancer patients.
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