Mechanism of crosslinking in benzoyl peroxide‐initiated functionalization of vinyltriethoxysilane onto polypropylene in the water medium

A Novel, Dual-Initiator, Continuous-Suspension Grafting Strategy for the Preparation of PP-g-AA-MAH Fibers to Remove of Indigo from Wastewater

The indigo dye found in wastewater from printing and dyeing processes is potentially carcinogenic, teratogenic, and mutagenic, making it a serious threat to the health of animals, plants, and humans. Motivated by the growing need to remove indigo from wastewater, this study prepared novel fiber absorbents using melt-blow polypropylene (PP) melt as a matrix, as well as acrylic acid (AA) and maleic anhydride (MAH) as functional monomers. The modification conditions were studied to optimize the double-initiation, continuous-suspension grafting process, and then functional fibers were prepared by melt-blown spinning the modified PP. The results showed that the optimum modification conditions were as follows: a 3.5 wt% interfacial agent, 8 mg/L of dispersant, 80% monomer content, a 0.8 mass ratio of AA to MAH, a 1000 r/min stir speed, 3.5 wt% initiator DBPH grafting at 130 °C for 3 h, and 1 wt% initiator BPO grafting at 90 °C for 2 h. The highest grafting rate of the PP-g-AA-MAH was 31.2%, and the infrared spectrum and nuclear magnetic resonance spectroscopic analysis showed that AA and MAH were successfully grafted onto PP fiber. This modification strategy also made the fibers more hydrophilic. The adsorption capacity of the PP-g-AA-MAH fibers was highly dependent on pH, and the highest indigo adsorption capacity was 110.43 mg/g at pH 7. The fiber adsorption capacity for indigo increased rapidly before plateauing with increasing time or indigo concentration, and the experimental data were well described in a pseudo-second-order kinetic model and a Langmuir isothermal adsorption model. Most impressively, the modified fiber adsorption capacity for indigo remained as high as 91.22 mg/g after eight regeneration and reuse cycles. In summary, the PP-g-AA-MAH fibers, with excellent adsorption-desorption characteristics, could be readily regenerated and reused, and they are a promising material for the removal of indigo from wastewater.

Cross-Linking of Polypropylene with Thiophene and Imidazole

In this work, two novel routes to synthesis cross-linked polypropylene (PP) are introduced by using two different precursors (2-thiophenemethyl amine (TMA) and 1-(3 aminopropyl) imidazole (API)), both cross-linked with 1,1′-(methylenedi-4,1-phenylene) bismaleimide (BM) at two different annealing temperature values (T = 50 °C and T = 150 °C). Both Diels–Alder (DA) and Michael addition reactions were successfully performed with TMA and API, respectively, albeit with different reactivity. Imidazole clearly shows a higher reactivity compared to thiophene. In addition, an increase in annealing temperature leads to a higher degree of cross-linking. The highest degree of cross-linking was obtained by the imidazole product after annealing at 150 °C (IMG1A150) as evident from the highest complex viscosity (|η*|) value of IMG1A150. A difference in rheology and thermal properties between the imidazole and thiophene cross-linked products was also observed. However, both products have superior melt properties and thermal stability compared with the starting material. They show processability at high temperatures. The melt flow behavior and de-cross-linking at higher temperatures can be tuned depending on the choice of imidazole or thiophene. This study shows an advance on the cross-linked PP processing and its product performances for further application on the commercial scale.

Cross-Linking of Polypropylene via the Diels-Alder Reaction

In this work, the possibility of preparing cross-linked polypropylene (PP) via Diels−Alder (DA) chemistry is explored. The overall strategy involves reaction of maleated polypropylene (the starting material), furfuryl amine (FFA), and bismaleimide (BM) as the cross-linking agent. The occurrence of reversible cross-linking was studied by checking the presence of relevant peaks in FTIR spectra, i.e., CH out-of-plane bending vibrations of the furan ring’s peak (γCH) at an absorption band of 730−734 cm−1, CH=CH of the BM aromatic ring’s stretching vibrations (υCH=CH) at an absorption band of 1510 cm−1, and the DA adduct (C-O-C, δDAring) at an absorption band of 1186 cm−1. In agreement with the spectroscopic characterization, the presence of a cross-linked network is also confirmed by rheology, namely the higher storage modulus (G′) compared with loss modulus (G″) value (G′ >> G″), as obtained via temperature sweep. Both the maleic anhydride (MA) content as well as the annealing temperature (50 °C and 120 °C) favor the DA reaction, while only partial de-cross-linking (retro DA) is observed at the higher temperature range of 150−200 °C. In addition, the products show higher mechanical robustness and thermal stability compared to the starting material.

EFFECTS OF GRAFTED VINYL TRIETHOXY SILANE ON MOISTURE CROSSLINKED EPDM

An EPDM terpolymer grafted with silane vinyl triethoxysilane (EPDM-g-VTES) was prepared by melt grafting, with dicumyl peroxide (DCP) as an initiator. Next, dibutyl tin dilaurate was added as a catalyst to promote moisture crosslinking of EPDM-g-VTES. By means of the rheological response of the rubber compound, Fourier transform infrared spectroscopy, and moving die rheometer, the VTES graft ratio and DCP partial crosslinking (pre-crosslinking) of EDPM-g-VTES were characterized to show the feasibility of moisture crosslinking. The mechanical properties of moisture crosslinked EPDM-g-VTES specimens were tested by universal material tester. The results showed that when the weight ratio of VTES to DCP was fixed at 15:1, the VTES graft ratio and DCP partial crosslinking of EDPM-g-VTES increased with the increase of VTES content. But the torque in the moisture crosslinking curve of EPDM-g-VTES increased significantly with the extension of crosslinking time, which proved that EPDM grafted with VTES was cured by moisture successfully. The tensile strength and elongation at break of EPDM-g-VTES were improved by moisture cure. Furthermore, the moisture cured specimen with 3 wt% VTES had the best mechanical performance.