The long-term photo-oxidative aging behavior of high-density polyethylene (HDPE) under different tensile stress was studied using a stress-aging apparatus. The aging behavior was investigated through the methods of the surface morphology observation, gel content measurement, Fourier transform infrared spectroscopy, and creep behavior. It was found that stress has influence on the development of cracks and stress induces cracking through creep deformation. With increasing stress, the cracking time decreases in a reversed S-shape curve way, and there is a critical stress near 7 MPa where the cracking time has a maximum decreasing rate. Meanwhile, the creep deformation increases rapidly when the stress exceeds the critical stress. The critical stress of HDPE is about 20–25% of breaking strength, and HDPE with low comonomer content has good dimensional stability when the stress is less than the critical stress, while HDPE with high comonomer content has a good performance when the stress exceeds the critical stress. This study may be useful for the rational selection of HDPE for the sheath material of bridge cable. POLYM. ENG. SCI., 55:2277–2284, 2015. © 2015 Society of Plastics Engineers

This article describes the structure changes of high-density polyethylene (HDPE) during stress and photo-oxidative aging experiments, and the relationship between different materials and cracking time. The three most representative grades of HDPE are 9070, TR480, and 2480NT. The average molecular weight, the comonomer type, and content of materials were measured by high-temperature gel permeation chromatography, ¹³C nuclear magnetic resonance (NMR) spectroscopy, and successive self-nucleation and annealing technique. Moreover, tensile testing was done to distinguish different toughness of materials. The samples were exposed to 5 MPa stress and ultraviolet irradiation in an aging oven, and observed at time intervals. The changes in structure were characterized by metallurgical microscopy, differential scanning calorimetry, attenuated total reflection-Fourier transform infrared spectroscopy, X-ray diffraction, and gel content measurements. With increasing time, the crystallinity increased, whereas melting point and oxygen induction times decreased. Meanwhile, the carbonyl index values and gel content reached about 10% until the samples were cracked. The results manifested that the resistance to cracking of the different HDPEs followed the order: 2480NT > TR480 > 9070. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40904.

In order to improve the photostability of polyoxymethylene (POM), a core-shell acrylate elastomer with UV stabilization, i.e. poly[(methyl methacrylate)-(butyl acrylate)-2-hydroxy-4-(3-methacryloxy-2-hydroxypropoxy)benzophenone] (core-shell poly(MMA-BA-BPMA)), was added into the POM matrix using a melt-mixing method. The effect of the modification with core-shell poly(MMA-BA-BPMA) on POM was compared with that of poly(MMA-co-BA-co-BPMA) copolymer. Scanning electron microscopy, metallographic microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction and X-ray photoelectron spectroscopy were employed to characterize POM blends before and after UV irradiation, and the mechanical properties of the POM blends were investigated. The results showed that core-shell poly(MMA-BA-BPMA) improved well the compatibility with and toughness of the POM matrix, and its light-stable functional groups could increase the UV resistance of POM blends. During UV aging, the impact strength and elongation at break of POM/core-shell poly(MMA-BA-BPMA) blends were retained, the growth rate of surface cracks of POM was inhibited effectively by core-shell poly(MMA-BA-BPMA) and the degree of photo-oxidation of POM blend surfaces was improved to a certain extent. Compared with poly(MMA-co-BA-co-BPMA), core-shell poly(MMA-BA-BPMA) had a better UV stabilization effect on the POM matrix. Our results indicate that the core-shell acrylate elastomer with toughening and UV stabilization functions can significantly improve the long-term UV stability of POM. Copyright © 2012 Society of Chemical Industry

In this study, an acrylate elastomer with light-stable functional groups was synthesized by methyl methacrylate (MMA), butyl acrylate (BA), and a polymerizable UV stabilizer 2-hydroxy-4-(3-methacryloxy-2-hydroxylproroxy) benzophenone (BPMA) via emulsion polymerization, and the product was poly[methyl methacrylate-co-butyl acrylate-co-2-hydroxy-4-(3-methacryloxy-2-hydroxylproroxy) benzophenone] [poly(MMA-co-BA-co-BPMA)]. The composition and characteristics of poly (MMA-co-BA-co-BPMA) were determined by using Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H-NMR), and ultraviolet–visible absorption spectroscopy (UV–vis). Further, the obtained poly(MMA-co-BA-co-BPMA) was blended with polyoxymethylene (POM) to modify its photostabilization, as well as the mechanical properties of POM composite were tested before and after UV irradiation. The result showed that poly(MMA-co-BA-co-BPMA) can be dispersed well in the POM matrix, which could play a role of improving compatibility with and toughening for POM, and its light-stable functional groups could increase the UV resistance of POM composite. Mechanical properties of modified POM were kept well with higher impact strength and elongation at break than pure POM after UV irradiation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Core–shell nanoparticles chemically functionalized by hindered amine stabilizer (HAS), poly(BA-MMA-co-PMPA) (PBMP), were prepared by two-stage emulsion polymerization from butyl acrylate, methyl methacrylate, and 1,2,2,6,6-pentamethylpiperidin-4-yl acrylate. The incorporation of HAS into the particles was confirmed by nuclear magnetic resonance (¹H-NMR) and the core–shell microstructure of PBMP particles was revealed by transmission electron microscopy. Furthermore, PBMP capable of one-step toughening and photostabilizing, was melt-blended with polyoxymethylene (POM), and its dispersion in POM was investigated by scanning electron microscope. The results showed that the core–shell nanoparticles could be well dispersed in POM matrix, indicating its good compatibility with POM. The UV resistance and impact resistance of POM were obviously improved by the HAS-functional core–shell nanoparticles simultaneously. In addition, the core–shell nanoparticles could confer excellent protection to the surface of POM from UV-light damage, regardless of the adverse effects on the thermal-oxidative stability of POM, as investigated by thermogravimetry analysis under aerobic condition. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A core–shell polyacrylate elastomer containing ultraviolet (UV) stabilizer was synthesized via semicontinuous seeded emulsion polymerization from butyl acrylate (BA), methyl methacrylate (MMA), and a polymerizable UV stabilizer 2-hydroxy-4-(3-methacryloxy-2-hydroxylproroxy)benzophenone (BPMA). The core–shell poly(MMA-BA-BPMA) was investigated by Fourier transform infrared spectroscopy, gel permeation chromatography UV–visible (UV–vis) absorption spectroscopy, and transmission electron microscope. Furthermore, the obtained core–shell poly(MMA-BA-BPMA) elastomer was used as a modifier to enhance the UV resistance and impact resistance of polyoxymethylene (POM). As studied by scanning electron microscope, the core–shell poly(BA-MMA-BPMA) elastomer could be well dispersed in POM matrix, indicating that the elastomer had good compatibility with POM. In addition, the POM/poly(MMA-BA-BPMA) blend was examined by differential scanning calorimetry before and after UV irradiation. The results showed that the melting point decreased as the irradiation time increased; however, the crystallinity culminated at 500-h UV irradiation slightly decreased and at last leveled off. The mechanical properties of POM/poly(BA-MMA-BPMA) before and after UV irradiation were also studied. It revealed that the photostabilizing fragments in the elastomer could provide long-term UV resistance to POM. Besides, the impact strength was also improved when compared with pure POM. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers