Application of the essential work of fracture concept to nanostructured polymer materials

The first part of the paper deals with a critical discussion of the methodical basis of essential work of fracture (EWF) concept with respect to the specimen geometry (especially the notch depth) and application to polymers. In the second part, an in situ testing device, which combines a tensile testing machine with an optical strain-field measuring system, has successfully demonstrated possibility of characterization of fracture behaviour of polystyrene-polybutadiene block copolymers and block copolymer/homopolymer blends as examples of nanostructured polymer materials. It has been shown that knowledge of the time evolution of the strain field close to the crack tips leads to a simple verification of the basic precondition for the applicability of the EWF concept, the precondition “plastic zone coalescence-before-stable crack propagation”.     

Processing and properties of engineering plastics recycled from waste electrical and electronic equipment (WEEE)

The characteristics of engineering plastics used in the preparation of electrical and electronic equipment were studied. More specifically, their thermal response was recorded by DSC experiments, the rheological properties were investigated via MFI tests and the mechanical properties were evaluated with tensile tests. The aim was to establish a procedure for recycling the same engineering plastics deriving from waste of electrical and electronic equipment (WEEE), which offers the additional advantage of using the as-received waste stream as a recyclable mixture, i.e. without sorting and classification of its components.The experimental results showed that blends of PC with ABS or ABS/HIPS can be prepared by direct mixing and this, would allow easy handling of the engineering plastics coming from WEEE, i.e. blending without the need of sorting. These mixtures can be easily processed and display acceptable mechanical properties with reasonable cost. Therefore, the processing characteristics and properties of the systems studied in this work could be the key for the design of an interesting approach for handling solid plastic waste from electrical and electronic devices.     

Morphology,structure, and properties of in situ compatibilized linear low‐density polyethylene/polystyrene and linear low‐density polyethylene/high‐impact polystyrene blends

Blends of linear low‐density polyethylene (LLDPE) with polystyrene (PS) and blends of LLDPE with high‐impact polystyrene (HIPS) were prepared through a reactive extrusion method. For increased compatibility of the two blending components, a Lewis acid catalyst, aluminum chloride (AlCl₃), was adopted to initiate the Friedel–Crafts alkylation reaction between the blending components. Spectra data from Raman spectra of the LLDPE/PS/AlCl₃ blends extracted with tetrahydrofuran verified that LLDPE segments were grafted to the para position of the benzene rings of PS, and this confirmed the graft structure of the Friedel–Crafts reaction between the polyolefin and PS. Because the in situ generated LLDPE‐g‐PS and LLDPE‐g‐HIPS copolymers acted as compatibilizers in the relative blending systems, the mechanical properties of the LLDPE/PS and LLDPE/HIPS blending systems were greatly improved. For example, after compatibilization, the Izod impact strength of an LLDPE/PS blend (80/20 w/w) was increased from 88.5 to 401.6 J/m, and its elongation at break increased from 370 to 790%. For an LLDPE/HIPS (60/40 w/w) blend, its Charpy impact strength was increased from 284.2 to 495.8 kJ/m². Scanning electron microscopy micrographs showed that the size of the domains decreased from 4–5 to less than 1 μm, depending on the content of added AlCl₃. The crystallization behavior of the LLDPE/PS blend was investigated with differential scanning calorimetry. Fractionated crystallization phenomena were noticed because of the reduction in the size of the LLDPE droplets. The melt‐flow rate of the blending system depended on the competition of the grafting reaction of LLDPE with PS and the degradation of the blending components. The degradation of PS only happened during the alkylation reaction between LLDPE and PS. Gel permeation chromatography showed that the alkylation reaction increased the molecular weight of the blend polymer. The low molecular weight part disappeared with reactive blending. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1837–1849, 2003     

Evaluation of the extent of the gel particle grafting of impact polystyrene

High Impact Polystyrene (HIPS) consists of a glassy polystyrene matrix and a rubber-like particle phase (gel phase). The extent of grafting of the gel phase is known to be an important parameter in the fracture toughness of the material. [1]. A simple quantitative model is developed in this paper to determine the extent of gel-particle grafting from the observed shifts in the glass transition temperature of the gel phase of three commercial types of HIPS.Although the increase in interfacial [2] and gel-particle grafting accounts for an increase in the energy absorbed before fracture at low strain rates, above a certain amount of grafting the material becomes embrittled at high strain rates. The adhesion factor A of mesophase models [3, 19], considered between the main phases of the material, was found to correlate with the observed impact behaviour.     

Chromatographic pattern in recycled high-impact polystyrene (HIPS) - Occurrence of low molecular weight compounds during the life cycle

The analysis of the chromatographic pattern of virgin, reprocessed, thermo-oxidised, and recycled high-impact polystyrene (HIPS) proves to be a suitable and sensitive tool to assess the degree of degradation of HIPS during its first life and subsequent recycling. Different low molecular weight compounds, such as residues of polymerisation, degradation products, and additives have been identified and relatively quantified in HIPS, using microwave-assisted extraction and further analysis by gas chromatography-mass spectrometry (GC-MS). The release of residues of polymerisation has been proven to occur during reprocessing, thermo-oxidation, and in recycled samples, which may show the emissions of volatile and semi-volatile organic compounds during the life cycle of HIPS. A wide range of oxidised degradation products are formed during reprocessing and thermo-oxidation; these products can be identified as oxidised fragments of polystyrene (PS), oxidised fragments from polybutadiene (PB) phase, and oxidised fragments from the grafting points between the PS and PB phase. Real recycled HIPS samples may also contain contaminations and fragments from additives included in their original formulations; the presence of brominated fragments from flame retardants in electronic waste is here observed.     

Characterization of high-impact polystyrene by catalytic pyrolysis over Al-MCM-41: Study of the influence of the contact between polymer and catalyst

In this work, the particular behaviour of a commercial high-impact polystyrene (HIPS) during the catalytic pyrolysis over Al-MCM-41 has been studied. The results obtained in a thermobalance showed differences in the number and/or the relative importance of the reaction steps involved in the pyrolysis, depending on the polymer particle size, which can be related to the differences in the nature of the polymeric phase being decomposed in each stage. Moreover, the relative importance of each step is very dependent on the particle size, revealing differences in the distribution of the different copolymer domains (i.e., styrene and butadiene domains) when the different particle size samples are mixed with the catalyst. The type of contact of the pure PS and PB polymers has also been studied revealing that, contrary to other results in literature, the catalyst may have an important effect both on the PS and PB pyrolysis. The results obtained showed that catalytic pyrolysis of these polymers could be a powerful tool for providing a fast and simple method for the characterization of copolymers of styrene and butadiene units.     

The co-pyrolysis of flame retarded high impact polystyrene and polyolefins

The co-pyrolysis of brominated high impact polystyrene (Br-HIPS) with polyolefins using a fixed bed reactor has been investigated, in particular, the effect that different types of brominated aryl compounds and antimony trioxide have on the pyrolysis products. The pyrolysis products were analysed using FT-IR, GC–FID, GC–MS, and GC–ECD. Liquid chromatography was used to separate the oils/waxes so that a more detailed analysis of the aliphatic, aromatic, and polar fractions could be carried out. It was found that interaction occurs between Br-HIPS and polyolefins during co-pyrolysis and that the presence of antimony trioxide influences the pyrolysis mass balance. Analysis of the Br-HIPS + polyolefin co-pyrolysis products showed that the presence of polyolefins led to an increase in the concentration of alkyl and vinyl mono-substituted benzene rings in the pyrolysis oil/wax resulting from Br-HIPS pyrolysis. The presence of Br-HIPS also had an impact on the oil/wax products of polyolefin pyrolysis, particularly on the polyethylene oil/wax composition which converted from being a mixture of 1-alkenes and n-alkanes to mostly n-alkanes. Antimony trioxide had very little impact on the polyolefin wax/oil composition but it did suppress the formation of styrene and alpha-methyl styrene and increase the formation of ethylbenzene and cumene during the pyrolysis of the Br-HIPS.     

Migration Testing of GPPS and HIPS Polymers: Swelling Effect Caused by Food Simulants Compared to Real Foods

Migration kinetic data from general purpose polystyrene (GPPS) and high impact polystyrene (HIPS) were generated for a set of model substances as well as styrene monomer and oligomers at different temperatures (20 °C, 40 °C, 60 °C) using food simulants stipulated in the European Regulation (EU) 10/2011 and real foods like milk, cream and olive oil (20 °C, 40 °C). The extent of polymer swelling was characterized gravimetrically and visual changes of the test specimens after migration contact were recorded. Isooctane and 95% ethanol caused strong swelling and visual changes of HIPS, overestimating real migration into foods especially at high temperatures; GPPS was affected by isooctane only at 60 °C. With 50% ethanol, after 10 days contact at 60 °C or 40 °C both polymers were slightly swollen. Contrary, most of the real foods analyzed caused no detectable swelling or visual changes of the investigated polymers. This study demonstrates that the recommendations provided by EU regulations are not always in agreement with the physicochemical properties of styrenic polymers. The critical point remains the selection of adequate food simulants/testing conditions, since the high overestimation of aggressive media can lead to non-compliance of polystyrene materials even if the migration into real food would be of no concern.     

尼龙1010分别与未接枝和接枝马来酸酐的高抗冲聚苯乙烯的共混体系研究

研究了尼龙１０１０（ Ｐ Ａ１０１０） 与高抗冲聚苯乙烯（ Ｈ Ｉ Ｐ Ｓ） 及马来酸酐官能化的 Ｈ Ｉ Ｐ Ｓ（ Ｈ Ｉ Ｐ Ｓ ｇ Ｍ Ａ） 间的相互作用,利用 Ｄ Ｓ Ｃ, Ｄ Ｍ Ａ, Ｓ Ｅ Ｍ 及拉伸测试等方法研究了不同组成比的共混物 Ｐ Ａ１０１０／ Ｈ Ｉ Ｐ Ｓ 与 Ｐ Ａ１０１０／ Ｈ Ｉ Ｐ Ｓ ｇ Ｍ Ａ 的结晶、玻璃化转变、形态及力学性能．结果表明 Ｈ Ｉ Ｐ Ｓ 与 Ｐ Ａ１０１０ 虽然结构相差甚远,但两者之间仍存在着一定的相互作用;而 Ｈ Ｉ Ｐ Ｓ ｇ Ｍ Ａ 可使 Ｐ Ａ１０１０ 的低温熔融峰变小,当 Ｈ Ｉ Ｐ Ｓ ｇ Ｍ Ａ 的含量≤５０ ％ 时,随着其含量的增加,共混物中 Ｐ Ａ１０１０ 的结晶温度升高;当含量＞ ５０ ％ 时, Ｐ Ａ１０１０ 发生分级结晶行为,其结晶温度由原来的１７８ ℃降至８３ ℃,同时 Ｈ Ｉ Ｐ Ｓ ｇ Ｍ Ａ 与 Ｐ Ａ１０１０ 间的相互作用变大, Ｄ Ｍ Ａ 谱上有明显的新的松驰峰． Ｐ Ａ１０１０／ Ｈ Ｉ Ｐ Ｓ ｇ Ｍ Ａ 共混体系的拉伸性能要优于相同组成的 Ｐ Ａ１０１０／ Ｈ Ｉ Ｐ Ｓ 体系．以上现象主要是由于 Ｈ Ｉ Ｐ Ｓ ｇ Ｍ Ａ 与 Ｐ Ａ１０１０ 中的端胺基发生了化学反应,产生了接枝共聚物 Ｐ Ａ１０１０ ｇ Ｈ Ｉ Ｐ     

纳米Sb_2O_3表面原位(共)聚合处理对HIPS纳米复合材料力学性能的影响

通用高分子材料的工程化和工程高分子材料的高性能化是高分子材料研究与开发的主要方向之一，核心、关键技术是高分子材料的同时增强、增韧，其中利用纳米无机刚性粒子与高分子材料复合是一条最简单而又行之有效的途径．由于无机纳米填料是亲水性的、表面能极高，有机高分子不能浸润填料或与填料表面相互作用弱，导致纳米粒子在高分子基体中易于团聚而分散性差，其复合材料力学性能低下．利用硬酯酸、非离子表面活性剂、表面辐照接枝处理纳米粒子表面忙，