Shrinkage Optimization in Talc- and Glass-Fiber-Reinforced Polypropylene Composites

Tomographic and Tension Analysis of Polypropylene Reinforced with Carbon Fiber Fabric by Injection Molding

The use of thermoplastic materials has had significant growth in recent years. However, with great mechanical requirements, thermoplastics have limitations to their use. To improve these restrictions, these materials are reinforced to obtain better properties. Polypropylene is one of the most versatile polymers and is used in almost all modern industries. Thus, the aim of this study is to create composite materials that offer performance for various industrial fields using carbon fiber fabric reinforcement, which is an inexpensive material widely used by the aerospace, automotive, and marine industries. The samples are produced by the over-injection molding of polypropylene. The investigation is focused on the impact of two critical control parameters in the injection molding process: temperature and pressure. Twelve experiments have therefore been considered, taking into account the combination of three factors: the presence or absence of carbon fiber fabric reinforcement, three levels of temperature (200 °C, 220 °C, and 240 °C), and two injection pressures (5000 kPa and 10,000 kPa). To evaluate the influence of these factors, three analyses were carried out: first, on the samples' shrinkage using a portable metrology-grade 3D laser scanner; second, on the internal defects using computed tomography (CT); and third, on the mechanical properties with tensile tests. From the results obtained, it is observed that the mold shrinkage fell slightly when PP samples were reinforced with carbon fiber, with both materials (PP and carbon-fiber-reinforced PP) having linear behavior with temperature. It is also noticed that polypropylene behaves as a crystalline material when processed at higher temperatures and pressures. From tests on the mechanical properties, it is concluded that the mean yield strength of PP-CF for injection temperatures of 220 °C and 240 °C represents an increase of 43% compared to the non-reinforced material.

Injection-Molded Isotactic Polypropylene Colored with Green Transparent and Opaque Pigments

Polypropylene (PP) belongs among the most important commodity plastics due to its widespread application. The color of the PP products can be achieved by the addition of pigments, which can dramatically affect its material characteristics. To maintain product consistency (dimensional, mechanical, and optical), knowledge of these implications is of great importance. This study investigates the effect of transparent/opaque green masterbatches (MBs) and their concentration on the physico-mechanical and optical properties of PP produced by injection molding. The results showed that selected pigments had different nucleating abilities, affecting the dimensional stability and crystallinity of the product. The rheological properties of pigmented PP melts were affected as well. Mechanical testing showed that the presence of both pigments increased the tensile strength and Young's modulus, while the elongation at break was significantly increased only for the opaque MB. The impact toughness of colored PP with both MBs remained similar to that of neat PP. The optical properties were well controlled by the dosing of MBs, and were further related to the RAL color standards, as demonstrated by CIE color space analysis. Finally, the selection of appropriate pigments for PP should be considered, especially in areas where dimensional and color stability, as well as product safety, are highly important.

Post-Molding Shrinkage, Structure and Properties of Cellular Injection-Molded Polypropylene

Cellular injection molding is a common method of modifying polymer materials aimed at reducing the sink marks on moldings' surfaces while reducing their weight. However, the dimensions of polypropylene (PP) samples as well as their mechanical properties after the injection molding process change as a result of re-crystallization. Knowledge of dimensional accuracy and awareness of the change in mechanical properties of products during conditioning are very important aspects in the polymer processing industry. The aim of this study was to assess the changes in the value of processing shrinkage and the size of the sink marks of porous PP moldings depending on the degree of porosity and the time since they were removed from the injection mold cavity. Studies of the structure and mechanical properties of moldings were carried out after several conditioning time intervals. The maximum conditioning time of samples was 840 h at 23 °C. Based on the analysis of the test results, it was found that the cellular injection molding process with the holding phase reduces the nucleation of gas pores, which results in a smaller reduction of sink marks than in the case of samples produced without the holding phase. However, PP moldings with a porosity degree equal to 8.9% were characterized by a higher shrinkage value after 1 h of conditioning, compared to moldings with porosity equal to 3.6%. The extension of the conditioning time also resulted in an increase in the value of linear shrinkage and the properties determined during tensile tests of solid and porous samples. Furthermore, in the case of samples with the highest porosity, the impact strength was reduced by about 30% after 840 h of conditioning compared to results obtained after 1 h.

Filling-Balance-Oriented Parameters for Multi-Cavity Molds in Polyvinyl Chloride Injection Molding

PVC injection molding has constrained temperature and shear rate owing to its temperature sensitivity and high viscosity, as well as its low conductivity. Many challenges are associated with the PVC injection molding process used for producing PVC fittings with a multi-cavity mold. Once filling imbalance occurs, the gates and/or runner of the mold should be changed by machine tools, which is time- and cost-intensive. Using Moldex3D and the Taguchi method, this study reveals an approach to eliminate imbalanced filling of multi-cavity molds for PVC injection molding. The injection rate optimization of the filling stage is successfully verified to reduce the imbalance. Furthermore, the temperatures of the molded PVC fittings are only slightly increased by the change in injection rate. The temperatures of fittings in the filling and packing are lower than the degradation temperature of PVC. This approach may help technicians to obtain pilot-run samples for the optimization of molding parameters and ensure degradation-free PVC molding.

Processing and Mechanical Properties of Highly Filled PP/GTR Compounds

Ground rubber from automobile tires is very difficult to recycle due to the cross-linking of the macromolecules and thus the lack of thermoplastic properties. The research consisted of assessing the processing possibility via the injection of highly filled PP/GTR compounds modified with 1.5 wt.% 2.5-dimethyl-2.5-di-(tert-butylperoxy)-hexane. GTR dosing ranged from 30 wt.% up to 90 wt.%. The evaluation of the processing properties of the obtained materials was carried out on the basis of the melt flow index test results and the signals recorded during processing by the injection molding by temperature and pressure sensors placed in the mold. The influence of the applied modifier on the changes in the mechanical properties of PP/GTR was determined with hardness, impact and static tensile tests. Moreover, thermal properties were obtained by the differential scanning calorimetry method. It has been found that it is possible to efficiently process compounds with high GTR content using injection molding. The presence of the filler allows to significantly reduce the cooling time in the injection mold and thus the time of the production cycle. It has been confirmed that 2.5-dimethyl-2.5-di-(tert-butylperoxy)-hexane modifies the rheological properties of PP and thus the PP/GTR composition. The lower viscosity of the matrix results in a more accurate bonding with the developed surface of the GTR grains, which results in better mechanical properties of the rubber-filled polypropylene.

Polypropylene Random Copolymer Based Composite Used for Fused Filament Fabrication: Printability and Properties

Fused filament fabrication (FFF) is one of the most commonly used additive manufacturing technologies. However, the applied material for commercial FFF is limited. Presently, though being one of the most used polymer materials, polypropylene (PP) is rarely used in FFF because of its serious warpage and shrinkage problems. This study investigated the impact of addition of short glass fibers (GF) and ethylene propylene diene monomer (EPDM) on the printability of polypropylene random copolymer (PPR) based FFF and mechanical properties of the printed samples, as well as other properties including rheology, thermal behaviors, and morphology. The results show that the modified PPR has excellent printability, as the printed samples are of good geometrical accuracy. The addition of GF can significantly improve the strength and modulus of the composite, but it also leads to serious decrease in toughness. EPDM addition can effectively improve the toughness of the composite, showing a complementary effect with GF. This work has important meaning in expanding the FFF applicable material and in broadening the application of PP.

Modification of Laser Marking Ability and Properties of Polypropylene Using Silica Waste as a Filler

Polypropylene (PP) belongs to the group of polymers characterized by low susceptibility to absorption of electromagnetic radiation in the infrared range (λ = 1064 nm). This research consisted of assessing the possibility of using silica waste from the metallurgic industry as an additive for PP laser marking. The modifier was introduced into the polymer matrix in the range from 1 to 10 wt%. The effects of laser radiation were assessed based on colorimetric tests and microscopic surface analysis. The mechanical properties of the composites were determined during the static tensile tests. The thermal properties were investigated via differential scanning calorimetry. It was found that the introduction of silica waste into polypropylene allows for the effective marking of sample surfaces with the use of a laser beam. The greatest contrast between the graphic symbol and the background was obtained for silica contents of 3 and 5 wt%, with the use of a low-speed laser head and a strong concentration of the laser beam. The application of silica caused an increase in the modulus of elasticity and the tensile strength of the composite samples. Increases in the crystallization temperature and the degree of crystallinity of the polymer matrix were also observed. It was found that silica waste can act as multifunctional additive for polypropylene.

Mechanical and Abrasive Wear Performance of Titanium Di-Oxide Filled Woven Glass Fibre Reinforced Polymer Composites by Using Taguchi and EDAS Approach

Two-body abrasive wear behavior of glass fabric reinforced (GC) epoxy and titanium dioxide (TiO₂) filled composites have been conducted out by using a tribo test machine. GC and TiO₂ filled GC composites were produced by the hand layup technique. The mechanical performances of the fabricated composites were calculated as per ASTM standards. Three different weight percentages were mixed with the polymer to develop the mechanical and abrasive wear features of the composites. Evaluation Based on Distance from Average Solution (EDAS), a multi-criteria decision technique is applied to find the best filler content. Based on the output, 2wt% TiO₂ filler gave the best result. Abrasive wear tests were used to compare GC and TiO₂ filled GC composites. The abrasion wear mechanisms of the unfilled and TiO₂ filled composites have also been studied by scanning electron microscopy. The outcome of the paper suggests the correct proportion of filler required for the resin in order to improve the wear resistance of the filled composites. Taguchi combined with Multi-Criteria Decision Method (MCDM) is used to identify the better performance of the TiO₂ filled epoxy composites.

Post-Processing Time Dependence of Shrinkage and Mechanical Properties of Injection-Molded Polypropylene

Dimensions of the injection-molded semi-crystalline materials (polymeric products) decrease with the time that elapses from their formation. The post-molding shrinkage is an effect of secondary crystallization; the increase in the degree of polymer crystallinity leads to an increase in stiffness and decrease in impact strength of the polymer material. The aim of this study was to assess the changes in the values of post-molding shrinkage of polypropylene produced by injection molding at two different temperatures of the mold (20 °C and 80 °C), and conditioned for 504 h at 23 °C. Subsequently, the samples were annealed for 24 h at 140 °C in order to conduct their accelerated aging. The results of shrinkage tests were related to the changes of mechanical properties that accompany the secondary crystallization. The degree of crystallinity of the conditioned samples was determined by means of density measurements and differential scanning calorimetry. It was found that the changes in the length of the moldings that took place after removal from the injection mold were accompanied by an increase of 20% in the modulus of elasticity, regardless of the conditions under which the samples were made. The differences in the shrinkage and mechanical properties of the samples resulting from mold temperature, as determined by tensile test, were removed by annealing. However, the samples made at two different injection mold temperature values still significantly differed in impact strength, the values of which were clearly higher for the annealed samples compared to the results determined for the samples immediately after the injection molding.

A Design of Experiment Approach for Surface Roughness Comparisons of Foam Injection-Moulding Methods

The pursuit of polymer parts produced through foam injection moulding (FIM) that have a comparable surface roughness to conventionally processed components are of major relevance to expand the application of FIM. Within this study, 22% talc-filled copolymer polypropylene (PP) parts were produced through FIM using both a physical and chemical blowing agent. A design of experiments (DoE) was performed whereby the processing parameters of mould temperatures, injection speeds, back-pressure, melt temperature and holding time were varied to determine their effect on surface roughness, Young’s modulus and tensile strength. The results showed that mechanical performance can be improved when processing with higher mould temperatures and longer holding times. Also, it was observed that when utilising chemical foaming agents (CBA) at low-pressure, surface roughness comparable to that obtained from conventionally processed components can be achieved. This research demonstrates the potential of FIM to expand to applications whereby weight saving can be achieved without introducing surface defects, which has previously been witnessed within FIM.

Improving the Dimensional Stability and Mechanical Properties of AISI 316L + B Sinters by Si3N4 Addition

The following paper describes a new and effective method to obtain high-density sinters with simultaneously decreased distortions, produced by one press and sinter operation. This effect was achieved through the induced disappearance of the eutectic liquid phase. The study was carried out on AISI 316L stainless steel powder that was mixed with elemental boron and silicon nitride. Boron was used as a sintering process activator. The scientific novelty of this publication consists of the use of a silicon nitride as a solid-state nitrogen carrier that was intended to change the borides’ morphology by binding boron. Based on the thermodynamic calculations, 20 blends of various compositions were tested for physical properties, porosity, microstructure, and mechanical properties. Moreover, phase compositions for selected samples were analyzed. It was shown that the addition of silicon nitride as a nitrogen carrier decreases the boron-based eutectic phase volume and both increases the mechanical properties and decreases after-sintering distortions. An explanation of the observed phenomena was also proposed.