Hydroxypropylmethylcellulose (HPMC) and hydroxypropylcellulose (HPC) are two polymers commonly used in various industries including pharmaceuticals, food, cosmetics and construction. Both are derivatives of cellulose and have similar chemical structures, but differ in their properties and applications.
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Chemical structure:
Hydroxypropyl methylcellulose (HPMC): HPMC is synthesized from natural cellulose through chemical modification of etherification. During this process, both hydroxyl groups of the cellulose molecule undergo substitution reactions. Methyl groups (-CH 3 ) were introduced to some of the hydroxyl groups, while hydroxypropyl groups (-CH 2 CH(OH)CH 3 ) were added to the remaining hydroxyl groups. This double substitution gives the polymer hydrophilic and hydrophobic properties, making it soluble in water and organic solvents.
Hydroxypropylcellulose (HPC): HPC, on the other hand, is produced by chemically modifying cellulose with propylene oxide. Unlike HPMC, which has introduced methyl groups, HPC mainly contains hydroxypropyl groups (-CH2CH(OH)CH3). This substitution results in an increased solubility of the polymer in organic solvents compared to native cellulose but retains some hydrophilic properties due to the presence of hydroxyl groups.
characteristic:
Solubility: HPMC is soluble in cold and hot water, forming a clear, viscous solution. It exhibits a phenomenon called "thermal gelation" in which the solution undergoes a reversible phase transition from liquid to gel as the temperature increases. HPC is also soluble in water, but to a lesser extent than HPMC. It forms colloidal solutions in water and exhibits better solubility in organic solvents such as ethanol, isopropyl alcohol and acetone.
Viscosity: HPMC and HPC are available in various viscosity grades for a wide range of applications. However, HPMC generally has a higher viscosity than HPC at equivalent concentrations, making it suitable for applications requiring thicker gels or coatings.
Film Formation: HPMC dries to form flexible, transparent films suitable for applications such as coatings, films and tablets. HPC also has film-forming properties but may produce films with slightly different properties, such as increased flexibility or moisture resistance based on degree of substitution and molecular weight.
Thermal Stability: HPMC generally exhibits good thermal stability, maintaining its performance over a wide temperature range. HPC also exhibits thermal stability but may undergo degradation at higher temperatures, especially in the presence of oxygen.
Manufacturing process:
HPMC: The production of HPMC involves several steps, including etherification of cellulose with propylene oxide to introduce hydroxypropyl groups, followed by methylation with methyl chloride to add methyl groups. The resulting product was then purified and dried to obtain the final HPMC powder.
HPC: HPC is typically produced by direct etherification of cellulose with propylene oxide, thereby introducing hydroxypropyl groups into the cellulose backbone. The degree of substitution and molecular weight of the polymer can be controlled by adjusting reaction conditions such as temperature, pressure and reaction time.
application:
HPMC: HPMC is widely used in pharmaceutical formulations as binders, disintegrants, controlled release agents and thickeners in tablet coatings. It is also used in construction materials such as cement-based mortars and plasters as a rheology modifier and water retaining agent. Additionally, HPMC is used in personal care products, food additives, and as a thickener in industrial processes.
HPC: HPC is primarily used in pharmaceuticals as a binder, film former, and viscosity enhancer in tablet formulations. Its solubility in organic solvents makes it suitable for use in coatings, especially enteric coatings and sustained-release formulations. HPC is also used in personal care products, food applications, and as a thickening agent in industrial processes, but to a lesser extent than HPMC.
advantage:
HPMC: The main advantages of HPMC include its versatility, biocompatibility, and ease of use in a variety of formulations. It has excellent film-forming properties, thermal stability and controlled release properties, making it a first choice for pharmaceutical and construction applications.
HPC: HPC offers advantages such as improved solubility in organic solvents, making it suitable for applications where water solubility is not required. It also provides good film-forming properties, viscosity control and compatibility capabilities with other excipients in pharmaceutical formulations.
Although HPMC and HPC have similarities in chemical structure as cellulose derivatives, they exhibit differences in properties, solubility, manufacturing processes, applications, and advantages. Understanding these differences is critical to selecting the right polymer for specific formulations and applications in different industries. Both polymers offer unique advantages and play important roles in pharmaceuticals, construction, personal care products and other industrial sectors, contributing to their widespread use and versatility in different applications.
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NISSO HPC (Hydroxypropyl Cellulose) is a modified cellulose obtained by reacting propylene oxide with cellulose. The presence of hydroxypropoxy group prevents the hydrogen bonding between the hydroxy groups on the cellulose chain, thereby making HPC soluble. NISSO HPC was first sold in Japan in and is globally approved for use in food product and as a pharmaceutical excipient. Nippon Soda has multiple manufacturing lines in Japan which have been fully IPEC GMP compliant since .
Regular Powder: Regular Powder (RP) type HPC is mainly used in solution form. As a binder for wet granulation applications, low viscosity grades of HPC give an excellent balance of properties to oral solid dosage tablets by imparting superior strength and elegance without compromise of the disintegration profile. As a film coating agent, HPC improves film flexibility, elongation, and adhesion to the tablet.
Fine Powder: Fine Powder (FP) type HPC has better formability than Regular Powder type and is mainly used in dry powder form. Having good wettability, lower viscosity grades are used as a dry-mix binder in high shear mixer formulations. Higher viscosity grades of HPC are applicable to controlled release matrix tablet formulations by direct compression application and give better release profiles compared to other common CR polymers.
Super Fine Powder: Super Fine Powder (SFP) type offers the highest level of formability. Excellent tablet properties can be obtained at low use level in direct compression applications. SFP is applicable to poorly compressible drug and high drug load formulations. Additionally, excellent tablet properties can be achieved in orally disintegration tablet (ODT) formulations by direct compression method when SFP grade is used in combination with a super disintegrator.
Granulation
NISSO HPC can be readily dissolved in both water and most organic solvents to prepare effective granulation solution. Poor flow and compaction actives can be successfully granulated using NISSO HPC to make tableting more feasible through both high shear wet granulation and fluidized bed granulation methods.
Direct compression and Roller Compaction
NISSO HPC is highly plastic and deformable, and exhibits high cohesive and adhesive forces, all important characteristics of a robust direct compression dry binder used for solid oral dosage forms. We often recommend HPC-SSL SFP for some of the most challenging direct compression formulations because of its super fine particle size, high plasticity and enhanced compressibility, allowing formulators to create tablets of outstanding quality.
Controlled release
Higher molecular weight/viscosity grades of NISSO HPC can be used for controlled release hydrophilic matrix tablets. Typical addition rate between 20-30% for effective delayed release of active ingredients are possible. HPC-M,H and VH are recommended.
Hydroxypropyl cellulose (HPC) with average aqueous viscosity of 300 mPa.s (NISSO HPC-M FP, d50=110μm) and 3,000 mPa.s (NISSO HPC-H FP, d50=110μm) from Nippon Soda, Japan. Hydroxypropylmethyl cellulose (HPMC) with average aqueous viscosity of 4,000 mPa.s (HPMC K4MCR,d50=100 μm) and 100,000 mPa.s (HPMC K100MCR, d50=100 μm) . A mixture of all ingredients (Table 1) was prepared in a free-fall blender and compressed to 200 mg, 8 mm bi-convex tablets containing 64 % Carbamazepine and 35 % CR polymer. For the dissolution test (USP) we have selected tablets with about 70 N breaking force. The release profile at 100 and 150 rpm was done in purified water as a dissolution medium.
&#;Powder Compactability
The compaction properties of the HPC-based powder were up to 3 times better compared with the HPMC-based (Figure 2).
With high drug dose and in absence of binder and filler, the HPC-based tablets demonstrated much better direct compression compactability compared to HPMC. It was necessary to add additionally 3 % of binder (micronized HPC-SSL SFP) in order to get an acceptable breaking forces with HPMC (Figure 2).
&#;Drug dissolution
Tablets with breaking force of 70 N (the maximal possible with HPMC K4MCR) were compared in dissolution test in demineralized water (Figure 3).
Being a poorly soluble drug, Carbamazepine (BCS II) release from hydrophilic matrix tablets is based on erosion of the CR polymer. As expected, at 100 rpm, the polymer with the lowest viscosity (HPC-M FP, 300 mPa.s) released the drug fastest that is driven by its quicker erosion/dissolution. The both cellulose ethers with similar viscosity (HPMC K4MCR and HPC-H FP) produced identical drug release and the CR agent with the highest viscosity demonstrated the lowest drug release rate (Figure 3).
With increase of the rotation speed to 150 rpm the picture was changed: whereas the HPC-based formulations showed minor changes in the dissolution profile, the HPMC-based tablets demonstrated a considerable increase of the drug release (Figure 4 and 5).
For HPC-M FP, drug release increased only 3-6 % with more hydrodynamic shear (faster ppm), demonstrating consistency and robustness. Comparatively, HPMC K4MCR drug release increased up to 20 % (Figure 4) with more shear.
Similar results were obtained when comparing HPC-H FP and HPMC K100MCR. The hydroxypropyl cellulose formulation demonstrated much better dissolution profile consistency and hydrodynamic stability (Figure 5).
&#;Results and discussion
While the demonstrated better compactability of HPC vs. HPMC can be explained with its superior toughness and plasticity, the better hydrodynamic stability needs further investigations. The numerous hydroxyl groups in the HPC molecule could be responsible for the formation of more new hydrogen bonds after hydration. This doesn&#;t mean necessarily stronger gel structure but eventually higher resistance to external mechanical stress. Thus, a formation of a more stable gel matrix with HPC provides more robustness under increased hydrodynamic conditions. The presence of methoxyl groups in the HPMC molecule could disturb the formation of multiple inter-molecular hydrogen bonds decreasing in this way the gel network stability compared to HPC.
&#;Conclusion
High viscosity grades NISSO HPC demonstrated better compactability and hydrodynamic stability compared to HPMC in controlled release hydrophilic matrix tablets with high dose carbamazepine. Additionally, NISSO HPC polymers demonstrated superior dissolution rate consistency and robustness compared to higher viscosity grades HPMC polymers.
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