Photodegradation of polypropylene/polystyrene blends: Styrene-butadiene-styrene compatibilisation effect

The mutual influence between the PP/PS polymer blend components during UV photodegradation was studied. Polypropylene (PP) and polystyrene (PS) have different photodegradation mechanisms, due to the larger UV absorption of polystyrene and formation of more stable tertiary carbon radicals. To compare the stabilities the kinetics of carbonyl formation was measured in different blend compositions. The results show that polystyrene presented a faster carbonyl formation than polypropylene, while the blends display faster kinetics than the isolated components. The kinetics of carbonyl formation of the blends was a function of polypropylene content. This result is unexpected if one considers the behaviour of each component alone. The kinetics and mechanism of UV degradation can be only explained taking into account the interaction between the blend components. PS absorbs UV light and energy is transferred to PP, which produces more reactive tertiary carbon free radicals. The effect of the interaction between the domains is enhanced when a compatibiliser is used, corroborating the hypothesis of energy transfer.     

The combined effect of photodegradation and stress cracking in polystyrene

This work aims to analyze the effects of photodegradation on the stress cracking resistance of polystyrene. Injection moulded samples were exposed to the ultraviolet light for various times in the laboratory prior to solvent contact. The bars were then stressed in a tensile testing machine under the presence of butanol. During this period the stress relaxation was monitored and the ultimate properties were evaluated after selected periods of stress cracking. Complementary tests were done by size exclusion chromatography and by scanning electron microscopy. The results indicated that butanol causes significant modification in polystyrene, with extensive surface crazing as well as reduction in mechanical properties. This is intensified under higher mechanical stress. The previous degraded samples showed a higher level of stress relaxation and a greater loss in tensile strength in comparison to the undegraded ones. The synergist action of photodegradation and stress cracking in polystyrene may be a consequence of the chemical changes caused by oxidation like the formation of polar chemical groups and the reduction in molecular weight.     

Sub-micron scale mechanical properties of polypropylene fibers exposed to ultraviolet and thermal degradation

Nanoindentation using atomic force microscopy (AFM) was conducted to investigate the affect of accelerated ultraviolet (UV) and thermal degradation on the mechanical properties of polypropylene fibers. The affect of degradation on Young’s modulus across fiber cross-sections was investigated with progressive nanoindentation from the surface to the center of the fiber. UV degradation initially increases the Young’s modulus both at the center and the surface of the fibers until 120 h of exposure with the increase being more rapid at the surface. Moduli started to decrease beyond 120 h of exposure. Wide angle x-ray scattering shows an increase of crystallinity up to 120 h of exposure and total destruction of crystallinity at 144 h. Infrared spectra showed the formation of carbonyl bonds with UV exposure. To investigate thermal degradation, the fibers were exposed to 125 °C for four weeks. Young’s modulus increased near the surface after four weeks exposure. These results support the idea that surface degradation may lead to embrittlement of textile fibers.     

Humidity dependence of carbon dioxide generation during photodegradation of biaxially oriented polypropylene in oxygen

UV generation of CO₂ gas from a range of biaxially oriented polypropylene (BOPP) films exposed in oxygen gas has been measured by in situ infrared spectrometry and compared with the development of absorption at 1713 cm⁻¹ due to carbonyl formation in the same films. As in studies of other polyalkene films, the CO₂ measurements, which take only 3 h, correlate well with carbonyl development measurements that require hundreds of hours.Upon UV irradiation of BOPP in dry oxygen an induction time of ∼60 min preceded a linear increase of photogenerated CO₂. In wet oxygen, no noticeable induction time preceded the linear increase of CO₂. The rate of CO₂ increase was greater when the oxygen was humidified. This pattern was observed for four different types of film and for films of different thickness. The increase in the rate of CO₂ photogeneration with increased humidity was greater for thicker films. The correlation between the amount of CO₂ generated and the strength of the carbonyl absorption developed under standard conditions was better for BOPP oxidation in dry than in humidified oxygen. The inclusion of recycled polymer caused an increase in the rate of photodegradation.Although measurements on each subset of films demonstrated a clear increase in the photogeneration of CO₂ at high humidity, the mechanism by which the CO₂ generation from BOPP is enhanced remains unclear and further work is necessary to resolve this puzzle.     

Evolution of phase dimensions and interfacial morphology of polypropylene/polystyrene compatibilized blends during mixing

The morphology development of polypropylene/polystyrene (PP/PS) blends was studied by means of effective mathematics methods. Time resolved fracture morphology measurements on PP/PS (20/80) blends compatibilized with styrene-butadiene-styrene block copolymer (SBS) suggested that PP/SBS domains acted as a warehouse supplying compatibilizer (SBS) to the phase boundary in the initial stage of mixing and promoted the formation and development of the transition layer. The development of the transition layer leaded to a more complicated morphology of fracture surface and strengthened the adhesion between phases, which was quantitatively investigated using Brown fractal dimension D_Brown. In the early stage of the mixing (<2.0 min), the mean chord length Λ_m used to describe the domain size decreased; simultaneously, the distribution of Λ trended to uniform as the mixing proceeded. After 2.0 min, Λ_m fluctuated in a definite range. Further, a normalized distribution of dimensionless domain sizes Λ/Λ_m was independent of mixing time, indicating that the late stage of phase dispersion can be scaled with a time-depended single length parameter Λ_m. In other words, the morphology development shows a possible dynamic scaling behavior.     

Carbon dioxide evolution and carbonyl group development during photodegradation of polyethylene and polypropylene

In situ infrared (FTIR) spectrometry has demonstrated that more CO₂ is photogenerated from polypropylene (PP) than from polyethylene (PE) films. Potential applications of the method include investigation of polymer degradation mechanism and ranking of polymer photo-stabilities in as little as 3 h.This study focuses on clarifying the mechanism of this rapid CO₂ formation from PE and PP, and complementary insight was obtained from changes in the IR transmission spectra of films irradiated by UVA for hundreds of hours. A 30 min induction time observed for CO₂ photogeneration from PP, but not PE, was reflected, on a much longer time scale, in the induction time for carbonyl development in PP, but not PE. This suggests that, in PP, the CO₂ induction time is a consequence of the slow development of carbonyl groups, a hypothesis that is supported by the elimination of the PP induction time when, prior to the CO₂ measurements, films are pre-exposed to UVA, to generate carbonyl groups. In addition, more CO₂ is evolved from both PE and PP films if they are pre-exposed.     

Effects of simulation conditions on antibacterial performance of polypropylene and polystyrene doped with HPQM antibacterial agent

2-Hydroxypropyl-3-piperazinyl-quinoline carboxylic acid methacrylate (HPQM) antibacterial agent in two different forms, solid form (HPQM-supported Neusilin absorbance; HPQM-neu) and liquid form (HPQM dissolved in deionized water; HPQM-water), were added to polypropylene (PP) and polystyrene (PS). The antibacterial performance against Escherichia coli and mechanical properties of the specimens were investigated. The effects of simulated conditions, including immersion in water (at room temperature and 80 °C), immersion in surfactant solution (at room temperature and 80 °C) and exposure to UV aging, on the antibacterial performance of specimens were also studied. The results showed that the optimal HPQM concentration for PP/HPQM-neu and PP/HPQM-water were 500 and 750 ppm, respectively, in order to reach 99.9% E. coli bacteria reduction, but those for PS/HPQM-neu and PS/HPQM-water were 1250 ppm. Addition of HPQM in both forms to PP and PS did not change the mechanical performance. HPQM-water was more appropriate and effective for antibacterial peformance for PP and PS than HPQM-neu. Immersion of all specimens in water and detergent solution (at room temperature and 80 °C) and UV aging decreased the antibacterial performance at different rates, the effect being very pronounced for the specimens with HPQM-neu.     

Effect of stabilizer and pigment on photodegradation of polypropylene as revealed by macromolecule scission and crosslinking measurements

Photodegradation depth-profiles have been generated using computer-aided molecular weight distribution analysis for 3 mm thick polypropylene injection moldings containing (i) a stabilizing package that included hindered amine light stabilizers and a phenolic stabilizer, (ii) titanium dioxide pigment and (iii) both the pigment and the stabilizing package. The inhibiting effect of the additives has been determined quantitatively by comparing macromolecule scission and crosslinking rates with those in samples containing no stabilizer or pigment. TiO₂ pigment gave more effective protection against molecular degradation than the stabilizer package; there was very little advantage to be gained by adding stabilizer when the pigment was present. The inhibition caused by having pigment or stabilizer present was measured to be very large: degradation was reduced by at least a factor of 10 and often by a factor of several hundred times. The relative amount of scission and crosslinking differed according to the additives present and the depth from the exposed surface: high reaction rates favoured scission and lower reaction rates resulted in a higher relative crosslinking concentration.     

Thermal degradation analysis and XRD characterisation of fibre-forming synthetic polypropylene containing nanoclay

Flammability of synthetic fibres is significantly worse than that of bulk polymers because of the high surface area to volume ratio and the low tolerance to high filler loadings in the fibre production process. Introducing nanocomposite structures has the potential to enhance the char formation at relatively low loadings of nanoparticulate fillers and hence can reduce the flammability of synthetic polymers and fibres.This paper reports thermal degradation analysis results in conjunction with TG analysis under different atmospheres and further studies of X-ray diffraction characterisation of fibre-forming polypropylene containing selected dispersed nanoclays.The concentrations of hydrocarbons, carbon monoxide and carbon dioxide released during the TG analysis have been monitored and analysed by using a combined electrochemical infrared analyser. The intensity changes of the crystallinity peaks and nanoclay peaks in the polymer and composites are discussed.     

Kinetics of thermal degradation and estimation of lifetime for polypropylene particles: Effects of particle size

The thermal stability and degradation behavior of polypropylene (PP) particles having diameter varying from few micrometers to nanometers were studied by thermogravimetric analysis (TGA). The PP particles of average diameter ∼20 μm, ∼10 μm, ∼5 μm, ∼1 μm and <500 nm were studied over a range of temperature from 25 to 600 °C in N₂ atmosphere and heating rates of 5, 10 and 15 °C/min. Thermal stability of PP particles initially decreases and then increases as particle size further decreases to nanometer scale. The five single heating rate techniques such as Friedman, Freeman-Carroll, Chang, Coats-Redfern and second Kissinger; and three multiple heating rate techniques such as the first Kissinger, Kim-Park and Flynn-Wall were used to compute the kinetic parameters of degradation reaction, e.g., activation energy (E_a), order of reaction (n) and frequency factor [ln(Z)]. The lifetime of macro-, micro- and nanosized PP particles was also estimated by a method proposed by Toop. It was found that the activation energy and lifetime of nanosized PP particles are moderately high compared to the microsized PP particles. Moreover, the decomposition temperature, order of reaction (n), frequency factor [ln(Z)] not only depend on the heating rate and calculation technique but also on the particle size of polymer. The results are compared with macrosized PP.     

Fabrication, morphology and thermal degradation behaviors of conductive polyaniline coated monodispersed polystyrene particles

This study describes the preparation of polyaniline (PANI) coated on the surface of monodispersed 400 nm polystyrene (PS) particles by in situ chemical oxidative polymerization. The monodispersed 400 nm PS particles served as cores were synthesized using the emulsion polymerization. Both images observed by field-emission scanning electron microscopy and transmission electron microscopy show the presence of a thin PANI layer uniformly coated on the surface of PS particle. The electrical conductivity of various amounts of PANI-coated PS particles is significantly increased about 13 orders of magnitude compared to that of the pristine PS particles. Differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) were used to investigate the thermal stability and thermal degradation behavior of PS and PANI-coated PS particles. Both DSC and TGA curves revealed that the coating of a thin PANI layer on the surface of PS can drastically increase the thermal stability of PS matrix. TGA isothermal degradation data illustrate that the activation energy of the PANI-coated PS particle is larger than that of PS. This phenomenon can be attributed to the incorporation of PANI coating on the surface of PS particle caused a decrease in the degradation rate and an increase in the residual weight for the PANI-coated PS particle.     

Thermal oxidative degradation kinetics of flame-retarded polypropylene with intumescent flame-retardant master batches in situ prepared in twin-screw extruder

The thermal oxidative degradation kinetics of pure PP and the flame-retarded (FR) PP materials with intumescent flame-retardant (IFR) master batches in situ prepared in twin-screw extruder were investigated using Kissinger method, Flynn-Wall-Ozawa method and Coats-Redfern method. The results showed that the activation energy order of PP and FR PP samples with different blowing agent/char former ratios obtained by Kissinger method agrees well with that obtained by Coats-Redfern one, which well illustrates the relationship between the composition of IFRs and their flame-retardancy, i.e. FR material with richer carbonization agent has higher activation energy for thermal oxidative degradation, hence leading to a better flame-retardancy. For Flynn-Wall-Ozawa method, due to its adoption of Doyle approximation, the obtained activation energy and its order of samples are very different from those of both Kissinger and Coats-Redfern methods. Criado method was finally used to determine the degradation reaction mechanism of various samples.     

Thermal degradation behaviors of a novel nanocomposite based on polypropylene and Co-Al layered double hydroxide

The thermal degradation behaviors of a novel nanocomposite based on polypropylene and organic Co/Al layered double hydroxide (PP/CoAl-LDH) were studied via thermogravimetric analysis (TGA) in the present work. The thermal degradation activation energies of the PP/CoAl-LDH nanocomposite were determined via Friedman and Flynn-Wall-Ozawa methods, and were compared with those of neat PP. The relationship between the organic CoAl-LDH concentration and the activation energies in PP/CoAl-LDH nanocomposite also has been investigated. An internal reason and an outer reason leading to high fire retardancy of PP/CoAl-LDH nanocomposite were proposed. The presence of CoAl-LDH tended to increase significantly the decomposition activation energy of nanocomposite at full-scale temperature and had an important influence on both of internal and outer reasons.     

Effect of a novel charring-foaming agent on flame retardancy and thermal degradation of intumescent flame retardant polypropylene

A new triazine polymer was synthesized by using cyanuric chloride, ethanolamine and ethylenediamine as raw materials. It is used both as a charring agent and as a foaming agent in intumescent flame retardants, designated as charring-foaming agent (CFA). Effect of CFA on flame retardancy, thermal degradation and mechanical properties of intumescent flame retardant polypropylene (PP) system (IFR-PP system) has been investigated. The results demonstrated that the intumescent flame retardant (IFR) consisting of CFA, APP and Zeolite 4A is very effective in flame retardancy of PP. It was found that when the weight ratio of CFA to APP is 1:2, that is, the components of the IFR are 64 wt% APP, 32 wt% CFA and 4 wt% Zeolite 4A, the IFR presents the most effective flame retardancy in PP systems. LOI value of IFR-PP reaches 37.0, when the IFR loading is 25 wt% in PP. It was also found that when the IFR loading is only 18 wt% in PP, the flame retardancy of IFR-PP can still pass V-0 rating, and its LOI value reaches 30.2. TGA data obtained in pure nitrogen demonstrated that CFA has a good ability of char formation itself, and CFA shows a high initial temperature of the thermal degradation. The char residue of CFA can reach 35.7 wt% at 700 °C. APP could effectively promote the char formation of the APP-CFA system. The char residue reaches 39.7 wt% at 700 °C, while it is 19.5% based on calculation. The IFR can change the thermal degradation behaviour of PP, enhance T_max of the decomposition peak of PP, and promote PP to form char, based upon the results of the calculation and the experiment. This is attributed to the fact that endothermic reactions took place in IFR charring process and the char layer formed by IFR prevented heat from transferring into inside of IFR-PP system. TGA results further explained the effective flame retardancy of the IFR containing CFA.     

Studies of photochemical transformations in polystyrene and styrene-maleic anhydride copolymer

Thin films of polystyrene (PS) and styrene-maleic anhydride copolymer (St-MAn) were exposed to monochromatic UV radiation (254 nm) for varied time intervals. The course of photochemical transformations was monitored by absorption spectroscopy (FT-IR, UV-vis) and thermogravimetry, which were also applied for the estimation of the thermal stability of samples studied. The changes of surface properties were monitored by contact angle measurements.Changes in chemical structure were found in irradiated films (inside and at the surface). The efficiency of photooxidative degradation in St-MAn copolymer was slightly lower than that in PS homopolymer but photo-crosslinking and chromophore formation were enhanced. An increase of hydrophilicity and oxidation degree in UV-irradiated samples was accompanied by destruction processes. The thermal stability of St-MAn was lower in comparison to polystyrene alone.The mechanism of photochemical reactions in the copolymer is proposed.     

Flammability and thermal degradation of flame retarded polypropylene composites containing melamine phosphate and pentaerythritol derivatives

The flammability of polypropylene (PP) composites containing intumescent flame retardant additives, i.e. melamine phosphate (MP) and pentaerythritol (PER), dipentaerythritol (DPER) or tripentaerythritol (TPER) was characterized by limiting oxygen index (LOI), UL 94 and the cone calorimeter, and the thermal degradation of the composites was studied using thermogravimetric analysis (TG) and real time Fourier transform infrared (RTFTIR). It has been found that the PP composite containing only MP does not show good flame retardancy even at 40% additive level. Compared with the PP/MP binary composite, the LOI values of the PP/MP/PER (PP/MP/DPER or PP/MP/TPER) ternary composites at the same additive loading are all increased, and UL 94 ratings of most ternary composites studied are raised to V-0 from no rating (PP/MP). The cone calorimeter results show that the heat release rate and smoke emission of some ternary composites decrease in comparison with the binary composite. It is noted from the TG data that initial decomposition temperatures of ternary composites are lower than that of the binary composite. The RTFTIR study indicates that the PP/IFR composites have higher thermal oxidative stability than the pure PP.     

Thermal recycling of polystyrene and polystyrene-butadiene dissolved in a light cycle oil

A study has been made of the cracking on a mesoporous silica of polystyrene (PS) and polystyrene-butadiene (PS-BD) dissolved in a light cycle oil (LCO) from a product stream of a commercial fluid catalytic cracking (FCC) unit. This study has been carried out in a reactor of short contact time (3 s) in the 723–823 K range. This strategy for simultaneous valorization of plastics and solvent avoids the technological problems inherent to the treatment of solid postconsumer-plastics and the limitation to heat transfer in the process of pyrolysis. The cracking of plastics has a synergistic effect on the conversion of LCO, as it contributes to increasing the yield of gasoline (C₅–C₁₂). The cracking of the PS/LCO blend produces high yields of styrene, whereas the cracking of the PS-BD/LCO blend produces a stream of products with petrochemical interest.     

Control of surface morphology of polypropylene/polystyrene blend pellets prepared by diffusion and subsequent polymerization of styrene in isotactic polypropylene pellets

Inhibitor hydroquinone (HQ) was added to the reaction system to prepare polypropylene/polystyrene (PP/PS) blend pellets without PS on the surface during diffusion and subsequent polymerization of styrene in isotactic polypropylene pellets. The effects of the amount of HQ on diametrical distribution of PS, surface morphology of the pellets and phase morphology inside the blend pellets were investigated.     

Morphologies, crystallinity and dynamic mechanical characterizations of polypropylene/polystyrene blends compatibilized with PP-g-PS copolymer: Effect of the side chain length

PP-g-PS copolymers were synthesized with the same polypropylene (PP) backbones and various side chain lengths of PS sequences via reactive comonomer p-allyltoluene (p-AT) by Ziegler–Natta copolymerization and the subsequent living anionic graft-polymerization. ¹H NMR characterized that the PP-g-PS copolymer had grafted 3.15 side chains per 1000 carbons in the PP backbones and the length of PS sequences varied in the range of 25.8–309.9 units. PP/PS blends with the PP-g-PS copolymer as compatibilizer (wt. 75/25/5) were prepared and characterized by SEM, WAXD and DMA to investigate the morphologies, crystallinity and glass transition temperatures of the PP/PS blends. All the results pointed out that the average side chain length (GL) of the graft copolymer (GL is from 25.8 to 309.9) made great effects of the PP/PS blends, such as the PS dispersed phase, the crystallinity of the PP component and the two glass transition temperatures of the blends, which showed the same trend with the increase of the GL. Overall, only with a suitable average side chain length, the PP-g-PS copolymer could achieve optimal compatibilizing efficiency of the PP/PS blends.     

Dilatometric studies of isotactic polypropylene with different morphology before and after thermal degradation in air

Summary Glass transition phenomenon in isotactic polypropylene has been studied in this paper basicly on dilatometric studies. New suggestions are made for explaining the occurrence of twoT _g values with their characteristic dependence on the degree of crystallinity of the samples having a different morphological structure. The effects produced by thermooxidation are discussed. T _g calledT _g1 is considered as the true glass transition temperature in the amorphous phase of IPP whereasTg2 is melting of a smectic phase in IPP,T _g2 >T _g1.Author thanks Prof. M. Kryszewski for useful discussion.