Impact Modifier Research Articles

Multistep Bulk‐/Gas‐Phase Polymerization of Propene in a Reaction Calorimeter

AbstractThis article outlines a kinetic study of two different Ziegler–Natta type catalysts in multistep bulk‐/gas‐phase polymerization of propene in a reaction calorimeter. In the first stage, bulk‐phase polymerization of propene, the matrix material is produced and kinetic information about the polymerization is extracted from power compensation calorimetry data. Focus is set on the influence of hydrogen on polymerization kinetics and comparing the performance of the two catalysts. In the 2nd stage, gas‐phase copolymerization of propene and ethylene, an elastomeric copolymer is produced as impact modifier and kinetic information is obtained from semibatch operation in constant conditions. The influence of monomer/comonomer ratio on copolymerization behavior of the two catalysts is investigated and compared.

Global coating additives markets, 2022–2027 – on acrylic, fluoropolymers, urethanes, metallic additives, anti-foaming, wetting and dispersion, rheology modification, biocides, & impact modifiers

Global coating additives markets, 2022–2027 – on acrylic, fluoropolymers, urethanes, metallic additives, anti-foaming, wetting and dispersion, rheology modification, biocides, & impact modifiers

Effects of core‐shell structured rubber on biobased polyamide 56 with stiffness and toughness balance

AbstractThere is great social awareness concerning the use of biobased materials of diminishing the rapid resource depletion and suppressing global warming. The inherent drawbacks of biobased polyamide 56 (PA56) such as poor notched impact strength limit its applications. Core‐shell structured impact modifiers consisting of a soft glycidyl methacrylate grafted poly(ethylene–octene) (POE‐g‐GMA) shell and a rigid polypropylene core were synthesized through the differences in interfacial tensions. Core‐shell rubber (CSR) particles were used to toughen biobased PA56 by melt blending. PA56/CSR composites exhibited a 560% increase in the impact strength, while the tensile performance loss was slight. This desirable toughness of biobased PA56 is attributed to the cavitation that occurred in POE‐g‐GMA shell which can induce shear bands and shear yielding, forming the fibrils. Characterizations, including X‐ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), melt rheological tests, and dynamic mechanical analysis (DMA) were conducted to study the toughening mechanism. The results indicated the massive shearing yielding, the cavitation of the CSR and interfacial debonding between the POE‐g‐GMA and the PP were the principal toughening mechanisms.

The correlation between serum total alkaline phosphatase and bone mineral density in young adults

BackgroundElevated total alkaline phosphatase (T-ALP) levels are usually indicative of enhanced osteoblastic activity and bone conversion status and are thus considered as a key factor needed for fresh bone mineralization and synthesis. To date, there is no consistent conclusion on the association between the serum T-ALP levels and bone mineral density (BMD). Therefore, the present study focused on exploring the association of serum T-ALP with lumbar BMD among young adults.MethodsThe present cross-sectional study included 6,331 subjects included in the National Health and Nutrition Examination Survey (NHANES) during 2011–2016. The participants aged 20–40 years included 3,349 males and 2,982 females. Serum T-ALP was our main variable, lumbar BMD was our outcome variable, and additional variables were the possible impact modifiers. The relations were analysed by the trend study, weighted multiple linear regression models, smooth curve fitting, and stratified analyses.ResultsIn a completely corrected multiple regression model, a negative association between serum T-ALP and lumbar BMD was discovered (β = -0.0007, 95% CI: –0.0009– –0.0005, P < 0.000001). After converting the continuous variable serum T-ALP into the categorical one, the significant negative association was still observed (P < 0.001), and in the subgroup and smooth curve fitting analyses, this negative correlation remained significant, too.ConclusionsOur study results indicated that serum T-ALP was negatively associated with lumbar BMD among young adults. Serum T-ALP measurement in the near future might become an effective biomarker to diagnose and treat osteoporosis on time.

On the slow crack growth process and associated structure–property relationships in polyamide 12 grades

AbstractThe influence of micro‐structural changes within polyamide 12 (PA12) grades on their resistance against crack initiation and subsequent Slow Crack Growth (SCG) was examined. Possible micro‐deformation mechanisms and processes guiding slow crack extensions in PA12 are discussed. Special focus was put on the formation of plastic zones as predecessors to microscopic cracks prior to crack initiation via crack freezing analysis. Simultaneously, variations in the pure SCG resistance after a recorded craze‐crack transition were determined via cyclic Cracked Round Bar (CRB) tests. In that context, a homologous series of PA12 grades of increasing molecular weight (MW), as well as a systematically developed series of PA12 grades incorporating a pigment and/or an impact modifier, were selected for this study. Results show a good correlation between the crack initiation resistance and the disentanglement resistance of PA12 chains as well as the size of the plastic zone. In that context, an increasing average MW, leads to increasing disentanglement resistances due to hydrogen bond effects. An impact modification promotes the development of notably larger plastic zones. Contrarily, colored grades exhibit a reduced plastic zone size, rendering a lower amount of dissipated energy before physical crack initiation. Pure SCG resistance follows a similar trend and is improved by high average MW as well as the use of impact modifier. Crack growth acceleration, however, is assumed to occur alongside the relatively weak interfaces between polymer matrix and pigments.

Sodium-glucose cotransporter 2 inhibitors do not increase the risk of fractures in real-world clinical practice in Korea: A national observational cohort study.

Aims/IntroductionThis study aimed to determine whether sodium–glucose cotransporter 2 inhibitors (SGLT2i) were related to increased fracture risk in adults with type 2 diabetes compared with dipeptidyl peptidase‐4 inhibitors (DPP‐4i).Materials and MethodsBetween 1 May 2016 and 31 December 2018, we carried out a new‐user cohort study using the Korean National Health Insurance Service database. Propensity score matching was carried out on 478,826 new users of an SGLT2i or DPP‐4i. After propensity score matching on >80 covariates, 84,460 individuals were initiated on SGLT2i or DPP‐4i, with 42,230 individuals in each treatment group. The time to first fracture event was compared between the SGLT2i and DPP‐4i groups using Cox proportional hazards models, and the results are reported as hazard ratios with 95% confidence intervals for fracture occurrence. Subgroup analyses investigated fractures between treatment groups according to baseline characteristics.ResultsIndividuals who were started on SGLT2i were not linked with increased fracture risk in both as‐treated and intention‐to‐treat analyses (as‐treated: hazard ratio 0.98, 95% confidence interval 0.92–1.04; intention‐to‐treat: hazard ratio 0.94, 95% confidence interval 0.89–1.00). We identified no significant interaction between the individuals' age, sex, fracture history or thiazolidinedione use in any subgroup analyses, showing that none of these variables appeared to be impact modifiers in the connection between SGLT2i and fractures.ConclusionsOur study found no increase in the risk of fracture among individuals treated with SGLT2i in a real‐world clinical setting for type 2 diabetes.

On the mechanical properties of melt-blended nylon 6/ethylene-octene copolymer/graphene nanoplatelet nanocomposites

Ethylene-octene copolymer (EOC) with a loading level of 20 wt%, maleated EOC (EOC-g-MA) with a loading level of 3 wt% and graphene nanoplatelets (GnPs) at four different loading levels, i.e., 3 wt%, 5 wt%, 10 wt% and 15 wt% were added to nylon 6 to prepare nanocomposites using a twin-screw extruder with a high shear rate screw running at 300 rpm. Increased stiffness was observed with the addition of GnPs while tensile strength of nanocomposites was only slightly influenced. Addition of GnPs into nylon 6 and nylon 6/EOC blend caused either a reduction in the Charpy impact strength or it remained unaffected. Similarly, the Izod impact strength of compatibilized nylon 6/EOC blend increased while that of nylon 6/EOC blend-based nanocomposites decreased. An increase was observed in the compressive Izod impact strength of compatibilized nylon 6/EOC blend. Addition of GnPs to nylon 6/EOC blend caused an increase in the fracture toughness due to their influence on the morphology and fracture mechanisms. This study shows that simultaneous addition of high surface area GnPs and an impact modifier to neat nylon 6 can help achieve enhancement and tailoring of stiffness and toughness.

Tailoring Poly(lactic acid) (PLA) Properties: Effect of the Impact Modifiers EE-g-GMA and POE-g-GMA.

Poly(ethylene-octene) grafted with glycidyl methacrylate (POE-g-GMA) and ethylene elastomeric grafted with glycidyl methacrylate (EE-g-GMA) were used as impact modifiers, aiming for tailoring poly(lactic acid) (PLA) properties. POE-g-GMA and EE-g-GMA was used in a proportion of 5; 7.5 and 10%, considering a good balance of properties for PLA. The PLA/POE-g-GMA and PLA/EE-g-GMA blends were processed in a twin-screw extruder and injection molded. The FTIR spectra indicated interactions between the PLA and the modifiers. The 10% addition of EE-g-GMA and POE-g-GMA promoted significant increases in impact strength, with gains of 108% and 140%, respectively. These acted as heterogeneous nucleating agents in the PLA matrix, generating a higher crystallinity degree for the blends. This impacted to keep the thermal deflection temperature (HDT) and Shore D hardness at the same level as PLA. By thermogravimetry (TG), the blends showed increased thermal stability, suggesting a stabilizing effect of the modifiers POE-g-GMA and EE-g-GMA on the PLA matrix. Scanning electron microscopy (SEM) showed dispersed POE-g-GMA and EE-g-GMA particles, as well as the presence of ligand reinforcing the systems interaction. The PLA properties can be tailored and improved by adding small concentrations of POE-g-GMA and EE-g-GMA. In light of this, new environmentally friendly and semi-biodegradable materials can be manufactured for application in the packaging industry.

The influence of hybrid flame retardant and impact modifier on recycled blends formulated from keyboard waste plastics: A study on its flame retardant, mechanical, thermal, and chemical properties

AbstractRecycled polymeric materials recovered from E‐waste, have gained importance in the recent years, due to the value addition of properties in the recycled materials. In the current work, a polymeric blends formulated from keyboard waste plastics was value added using a flame retardant (FR), and these plastics are not incorporated with FR during its processing. This work was carried out to enhance the FR property of polymers recovered from keyboard waste, and to study the effects of these additives on the mechanical properties of the polymeric blends. The FR tri phenyl phosphate (TPP), and a hybrid FR combining TPP with sepiolite, was added in different proportions to the blend. The FR blends were analyzed with UL‐94 and LOI and it was observed that the blends with hybrid FR showed higher FR properties, as the results of UL‐94 and LOI showed V‐1 and 29%, respectively. The cone calorimetry results showed that the peak heat release rate of the blends was improved from 704 to 533 KJ/m2. The gas and condensed phase reaction has been explained with an illustration. FTIR and TGA with and without the FR were performed. The mechanical properties of the blends drastically reduced after the addition of FRs, hence an impact modifier was added in order to regain the lost mechanical properties, and a morphological analysis was carried out to compare the influence of impact modifier in the polymeric blend.

A systematic study on the synergistic effects of MWCNTs and core\u2013shell particles on the physicomechanical properties of epoxy resin

Here, core–shell impact modifier particles (CSIMPs) and multiwalled carbon nanotubes (MWCNs) were used as reinforcing agents for improving the toughness and tensile properties of epoxy resin. For this purpose, emulsion polymerization technique was exploited to fabricate poly(butyl acrylate-allyl methacrylate) core-poly(methyl methacrylate-glycidyl methacrylate) shell impact modifier particles with an average particle size of 407 nm. It was revealed that using a combination of the prepared CSIMPs and MWCNTs could significantly enhance the toughness and tensile properties of the epoxy resin. Also, it was observed that the dominant factors for improving the fracture toughness of the ternary composites are crack deflection/arresting as well as enlarged plastic deformation around the growing crack tip induced by the combination of rigid and soft particles. The Response Surface Methodology (RSM) with central composite design (CCD) was utilized to study the effects of the amounts of CSIMPs and MWCNTs on the physicomechanical properties of the epoxy resin. The proposed quadratic models were in accordance with the experimental results with correlation coefficient more than 98%. The optimum condition for maximum toughness, elastic modulus, and tensile strength was 3 wt% MWCNT and 1.03 wt% CSIMPs. The sample fabricated in the optimal condition indicated toughness, elastic modulus, and tensile strength equal to 2.2 MPa m1/2, 3014.5 MPa, and 40.6 MPa, respectively.

Structure-Property Relationships of Polyamide 12 Grades Exposed to Rapid Crack Extension.

Thermoplastic materials have established a reputation for long-term reliability in low-pressure gas and water distribution pipe systems. However, occasional Slow Crack Growth (SCG) and Rapid Crack Propagation (RCP) failures still occur. SCG may initiate only a small leak, but it has the potential to trigger RCP, which is much rarer but more catastrophic and destructive. RCP can create a long, straight or meandering axial crack path at speeds of up to hundreds of meters per second. It is driven by internal (residual) and external (pressure) loads and resisted by molecular and morphological characteristics of the polymer. The safe installation and operation of a pipe throughout its service lifetime therefore requires knowledge of its resistance to RCP, particularly when using new materials. In this context, the RCP resistance of five different polyamide (PA) 12 grades was investigated using the ISO 13477 Small-Scale Steady State (S4) test. Since these grades differed not only in molecular weight but also in their use of additives (impact modifiers and pigments), structure-property relationships could be deduced from S4 test results. A new method is proposed for correlating these results more efficiently to evaluate each grade using the crack arrest lengths from individual S4 test specimens.

Durable Polylactic Acid (PLA)-Based Sustainable Engineered Blends and Biocomposites: Recent Developments, Challenges, and Opportunities

The paper comprehensively reviews durable polylactic acid (PLA)-based engineered blends and biocomposites supporting a low carbon economy. The traditional fossil fuel derived nonrenewable durable plastics that cannot be circumvented have spawned increased environmental concerns because of the continuous rise of their carbon footprint during processing and disposal. It is anticipated that the production of biodegradable and nonbiodegradable (durable) plastics from the year 2020 to 2025 will rise ∼47% and ∼21%, respectively. The carbon footprint can be reduced in durable (nonrenewable) plastics by decreasing or replacing the “fossil carbon” content with “renewable carbon” content. The replacement will enable us to attain a sustainable environment, a low carbon footprint, energy security, and effective resource management. Thus, PLA-based durable products need to be developed with an enhanced service life that strikes a balance between environment-friendliness and product performance for engineering high-performance applications. The recent progress for enhancing the durability of PLA-based products consisting of hybrid nonrenewable and renewable carbon has been attained by incorporating synthetic plastics, synthetic fibers (glass and carbon), natural fibers, and other biofillers (biocarbon). Further, the effects of additives such as initiators, nucleating agents, chain extenders, compatibilizers, impact modifiers, and toughening agents to prepare such blends and composites have been discussed. This Review further critically examines the advances centering on processability, heat resistance, flame retardancy, strength, and toughness. In addition to that, current and prospective applications such as automotive, electronic, medical, textile, and housing of PLA-based products are discussed. However, the challenges for tailoring durable PLA-based products that still need to be addressed, such as improved processability, striking stiffness–toughness balance, enhanced heat resistance, and improved interfacial adhesion between the polymer–polymer, polymer–filler, and hybrid polymer–filler in respective polymer blends, composites, and hybrid composites, are summarized and analyzed in this Review. Hence, the opportunities for improvement to overcome the challenges lie ahead.

Complex structures formed by combination of polymer-grafted GO and impact modifier in epoxy

Parameters of epoxy can be effectively improved using polymer-grafted GO. This study reveals so far unknown structure-directing performance of single- and bimodally-grafted GO in impact-modified epoxy. Bimodal grafting leads to formation of lamellae with less ordered more distant GO and fair mobility of grafted dissimilar chains due to their repulsive interactions, resulting in favourable effect on mechanical properties of epoxy . Unlike single-grafted GO with aligned plates, this ordering is not disturbed by added rubber which is more markedly incorporated even as layered domains into lamellae. Formation of more complex structures controlled by grafting geometry was also found. Structure–properties relationships indicate low contribution of added rubber, both as single inclusions or incorporated into ordered GO domains, which confirms high effectivity of lamellar structure with linked polymer chains of relatively high mobility.

Poly(2,6-dimethyl-1,4-phenylene ether)/poly(phenylene sulfide)/styrenic block copolymer blends compatibilized with reactive polystyrene

Blends of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(phenylene sulfide) (PPS) have shown potential as a new class of high-performance engineering plastics by reciprocally complementing the drawbacks of each component. However, improving their inherently poor toughness remains a challenge. Here, we report the design of PPE/PPS-based quaternary blends with increased impact strength without a significant loss of mechanical and flame-retardant properties. Introducing reactive polystyrene (RPS) with an oxazoline functional group as a compatibilizer improved the miscibility between the discrete PPE domain and continuous PPS matrix phases. The impact modifier styrene-ethylene-butadiene-styrene (SEBS) was compatibilized within the PPS matrix phase in the presence of RPS, enabling extraordinary impact strength. The tensile strength of the quaternary blends decreased slightly with increasing SEBS content, but the values exceeded the criteria for engineering plastic. All quaternary blends passed the V-0 grade in the UL-94 test because of the inherently excellent flame retardancy of the majority components.

Synthesis of Styrenic Triblock Copolymer and its Application in Polyester Blends

AbstractThis work deals with the synthesis of functional impact modifier Polystyrene–block‐Polybutyl acrylate‐block‐Poly(Styrene‐co‐acrylic acid) (PS‐b‐PBA‐b‐P(S‐co‐AA)) triblock copolymer through atom transfer radical polymerization. This triblock copolymer is characterized by FTIR, 1H NMR, and GPC. Compatibilizing effect of synthesized impact modifier PS‐b‐PBA‐b‐P(S‐co‐AA) is studied in polymer blends of Polyethylene terephthalate (PET) and Polystyrene (PS). Mechanical, rheological, and morphological properties of PET/PS blend are studied.

HIV Engage—A randomized controlled efficacy trial of an acceptance-based behavioral therapy intervention to improve retention in care for HIV treatment naïve patients: Study protocol

IntroductionPeople with HIV (PWH) who are not consistently retained in medical care, particularly when they are first diagnosed, are at risk for: delayed antiretroviral therapy (ART) initiation, suboptimal ART adherence, unsuppressed viremia, and mortality. Suboptimal retention means effective ART cannot be leveraged to prevent onward HIV transmission. To address this, we developed and previously pilot tested the HIV Engage intervention—a novel behavioral approach to enhance retention in HIV care using acceptance-based behavioral therapy (ABBT)—and established feasibility and acceptability of this approach. In the current study, we investigate the efficacy of ABBT compared to an attention-matched control condition in a full-scale randomized controlled efficacy trial. MethodsTwo hundred seventy HIV care naïve patients from geographically diverse clinics will be recruited and equally randomized to receive (a) the HIV Engage intervention, consisting of two 20–30 min ABBT sessions delivered in-person or remotely, or (b) an attention-matched HIV education control condition. Primary outcomes are number of HIV care appointments kept and HIV viral load suppression. Secondary outcomes are higher self-reported ART adherence, HIV status disclosure, increased social support, and reductions in perceived HIV stigma. Hypothesized mediators include acceptance of one's HIV diagnosis and willingness to disclose serostatus. We will also assess for epidemiologically-linked moderators of the treatment effect. ConclusionsABBT represents a novel, potentially promising approach to enhance retention in ongoing HIV care among treatment naïve PWH. This study will contribute significant actionable data establishing the impact, mediational mechanisms, and effect modifiers of ABBT.

Reactive processing of PA6/EPDM‐MA blends as modifier for application and development of high‐performance polypropylene

AbstractIn this work, PA6/EPDM‐MA was added as an impact modifier for high‐performance polypropylene (PP) production. PA6/EPDM‐MA compounds were processed in an internal mixer, aiming at chemical reaction between maleic anhydride of EPDM‐MA and the amine terminal groups of PA6. Afterward, PP/(PA6/EPDM‐MA) blends were processed by extrusion and injection molding. Rheological properties were evaluated using torque rheometry; additionally, Fourier transform infrared spectroscopy, Molau test, impact and tensile strengths, Shore D hardness, thermal deflection temperature, X‐ray diffraction, differential scanning calorimetry, thermogravimetry, water absorption, contact angle, and scanning electron microscopy tests were performed in injected specimens. PP/(PA6/EPDM‐MA) with 70/(15/15)% displayed quite high increase in impact and elongation at break, with gains of 850% and 265%, compared to neat PP. There were no drastic losses in tensile strength, elastic modulus, and Shore D hardness, due to PA6 addition. A significant increase was seen in the thermal stability of PP/(PA6/EPDM‐MA), corroborating the increase in structural stability seen in HDT. SEM images showed high interfacial adhesion between PP and PA6/EPDM‐MA corroborating higher mechanical properties. Summing up, PA6/EPDM‐MA premix acted as an efficient impact modifier for PP. Acquired data show that P6/EPDM‐MA system was effective in developing high‐performance PP with potential for application in the automotive and electronics industries.

Degradation of Styrenic Plastics during Recycling: Accommodation of PP within ABS after WEEE Plastics Imperfect Sorting.

With the development of dark polymers for industrial sorting technologies, economically profitable recycling of plastics from Waste Electrical and Electronical Equipment (WEEE) can be envisaged even in the presence of residual impurities. In ABS extracted from WEEE, PP is expected to be the more detrimental because of its important lack of compatibility. Hence, PP was incorporated to ABS at different rates (2 to 8 wt%) with a twin-screw extruder. PP was shown to exhibit a nodular morphology with an average diameter around 1–2 µm. Tensile properties were importantly diminished beyond 4 wt% but impact resistance was decreased even at 2 wt%. Both properties were strongly reduced as function of the contamination rate. Various potential compatibilizers for the ABS + 4 wt% PP system were evaluated: PPH-g-MA, PPC-g-MA, ABS-g-MA, TPE-g-MA, SEBS and PP-g-SAN. SEBS was found the most promising, leading to diminution of nodule sizes and also acting as an impact modifier. Finally, a Design Of Experiments using the Response Surface Methodology (DOE-RSM) was applied to visualize the impacts and interactions of extrusion temperature and screw speed on impact resistance of compatibilized and uncompatibilized ABS + 4 wt% PP systems. Resilience improvements were obtained for the uncompatibilized system and interactions between extrusion parameters and compatibilizers were noticed.

Impact Modifiers and Compatibilizers for Versatile Epoxy-Based Adhesive Films with Curing and Deoxidizing Capabilities.

Epoxy resins with acidic compounds feature adhesion, robustness, and deoxidizing ability. In this study, hybrid adhesive films with deoxidizing and curing capabilities for semiconductor packaging were fabricated. The compatibilizing effects and mechanical properties were chiefly investigated by using various additive binders (thermoplastic amorphous polymers) and compatibilizing agents. The curing, deoxidizing, thermal, and rheological properties were systematically investigated. For uniform film formation and maximizing deoxidizing curable abilities, a thermoplastic–thermoset mixture containing a phenyl and carboxylic acid-based additive (benzoic acid), and a polycarbonate was chosen as the model adhesive film. Without either a phenyl or an acidic group in the compatibilizing agent, deoxidizing and compatibilizing effects were not achieved. The manufactured hybrid adhesive film can be effectively used, especially for electronic devices that require deoxidization and adhesion.

Development of Toughened Flax Fiber Reinforced Composites. Modification of Poly(lactic acid)/Poly(butylene adipate-co-terephthalate) Blends by Reactive Extrusion Process.

The presented study focuses on the development of flax fiber (FF) reinforced composites prepared with the use of poly(lactic acid)/poly(butylene adipate-co-terephthalate)—PLA/PBAT blend system. This type of modification was aimed to increase impact properties of PLA-based composites, which are usually characterized by high brittleness. The PLA/PBAT blends preparation was carried out using melt blending technique, while part of the samples was prepared by reactive extrusion process with the addition of chain extender (CE) in the form of epoxy-functionalized oligomer. The properties of unreinforced blends was evaluated using injection molded samples. The composite samples were prepared by compression molding technique, while flax fibers reinforcement was in the form of plain fabric. The properties of the laminated sheets were investigated during mechanical test measurements (tensile, flexural, impact). Differential scanning calorimetry (DSC) analysis was used to determine the thermal properties, while dynamic mechanical thermal analysis (DMTA) and heat deflection temperature (HDT) measurements were conducted in order to measure the thermomechanical properties. Research procedure was supplemented with structure evaluation using scanning electron microscopy (SEM) analysis. The comparative study reveals that the properties of PLA/PBAT-based composites were more favorable, especially in the context of impact resistance improvement. However, for CE modified samples also the modulus and strength was improved. Structural observations after the impact tests confirmed the presence of the plastic deformation of PLA/PBAT matrix, which confirmed the favorable properties of the developed materials. The use of PBAT phase as the impact modifier strongly reduced the PLA brittleness, while the reactive extrusion process improves the fiber-matrix interactions leading to higher stiffness and strength.